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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
151 - 200 of 1034 results
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Impact of Facies-related Diagenesis on the Heterogeneity of Reservoir Sandstones - Obaiyed Field, Western Desert, Egypt
Authors R. Badr, M. El-Anbaawy and A. El-KammarSummaryThe Obaiyed field is one of the largest gas producing fields in the Western Desert of Egypt. It mainly produces from the Jurassic Lower Safa sandstones at a depth of some 4000 m. Integrated sedimentologic and petrographic investigations were carried out for conventional cores from seven wells cut in the reservoir-bearing interval so as to study the reservoir quality controlling factors and try to predict the reservoir quality distribution in the area. Interpretation of the lithofacies associations has supported the estuarine depositional model proposed by earlier workers in which channel systems (tidally-influenced fluvial channel, tidal channel, distributary channel and estuarine channel), bay head delta, flood tidal delta, lagoon, shoreface and flood plain complex are the main depositional facies encountered. Several diagenetic features of compaction, cementation, dissolution and replacement related to both eogenetic and mesogenetic regimes were identified. The most significant authigenic minerals recorded are quartz overgrowths, kaolin, illite, siderite and pyrite; showing a complex compositional multiphases and microtextural variations. The relationship between the depositional facies types and their corresponding reservoir qualities showed that: 1-Each depositional facies is characterized by definite reservoir quality range, 2-Both the distributary channel and shoreface facies show the best reservoir quality. Conversely, the flood delta, fluvial channel, estuarine channel and tidal channel facies represent the lowest reservoir quality.
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Investigation of Diagenetic Alteration, Mineralization And Stream Sediment Geochemistry in Chehregan Sedimentary Basin
Authors M. Panahzadeh and R. MasoumiSummaryChehregan area is located in the NW Iran. Lithologic units in this area have coarse-grained clastic-continental facies of Tertiary age and underlain unconformably by older formations. The clastic-contonental units begin with various kinds of marls overlain by a series of clastic and clastic-carbonate units.
Two conspicuous diagenetic alteration zones were developed at Chehregan; (1) oxidized and (2) leached. Reddening occurred at early diagenetic stage while brown sediments interacted with oxidizing pore solutions. Bleaching took place within red beds at late in diagenetic stage while the passing of reducing solutions dissolved and leached the preexisting iron oxides yielding a gray color layer along the conduit. Copper mineralization was developed as lenticular forms within the bleached and leached alteration zones. The important factors controlling the development of this zone are the presence of abundant pyrite and fragments of organic matters as reducing agents and also the permeability of the host rocks that facilitate the passage of oxidizing copper-bearing solutions.
Some characteristics of mineralized zone including lithology, mineralogy, lenticular and layered-shape of mineralized zone, replacement and dessiminated textures of copper-bearing minerals, and the presence of remnants of organic matters associated with copper mineralization provide sufficient evidence for categorizing this copper-bearing layers as Redbed-type.
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The Importance of Locally Converted Shear Waves in the Thin Layers AVO Response - A Physical Modeling Study
Authors C. A. Martins de Assis, S.A.M. Oliveira, R.M. Missagia and M.A.R. CeiaSummaryThis work aimed to study the seismic amplitude response of two physical models, one composed of thin water layer and the other of an acrylic thin layer. Physically modeled data was chosen as the reference for the amplitude analysis because this kind of modeling reproduces real wave propagation phenomena. Common midpoint data were acquired over each physical model using semi-spherical piezoelectric transducers. Then the data were processed to remove linear noise and to compensate amplitudes for effects like source/receiver directivity, geometric spreading and transmission losses. Finally, the experimental AVO behavior and the AVO obtained from numerical modeling through the reflectivity method were compared. It was observed that local P-SV mode conversions may influence considerably the thin layer AVO behavior and internal multiple reflections generally have low order effects. The reflectivity method parameterized with the experimental wavelet and in a separate modeling with a Ricker wavelet, in the same frequency bandwidth of the experimental wavelet, modeled experimental reflection data with high precision.
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Joint PP-PS Inversion Based on The Reflectivity Method
More LessSummaryAVO inversion is the most commonly used practice in seismic exploration. Although quite successful, it has inherent assumption that the amplitude of seismic data only depends on the reflection coefficients, neglecting the wave propagation effects, which leads to unreliable inversion results. Hence wave propagation effects should be fully corrected before inversion. However, it is not always achievable, for example, the compensation of transmission loss and multiples removal in thin-interbed are next to impossible. In this paper, we propose a joint PP-PS inversion based on the reflectivity method to makes up aforementioned deficiency of traditional AVO inversion. The reflectivity method assumes the underground is layered media and is able to simulate full wave field, including the reflection, transmission, transformation of all wave forms, and even multiples, which means that the transmission loss and multiples can be considered in our inversion technique. Therefore, seismic data of thin-interbed with transmission losses and multiples can be directly input for inversion and achieve accurate results. The application on a numerical model and real data demonstrate the validity and accuracy of this method.
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Modeling and Analysis of Frequency-dependent AVO Attributes for Fluids Saturation Prediction
More LessSummaryPrestack amplitude-versus-offset (AVO) inversion and interpretation has successfully helped to characterize and detect hydrocarbon reservoirs for many years. Recently, many geophysicists are studying frequency-dependent attributes for quantitative hydrocarbon detection. In this abstract, we analysis the two frequency-dependent AVO attributes (intercept and gradient) by modeling the different gas and water saturation condition based on patchy saturated model. The main aim is to analyze the frequency-dependent characteristic with a gas saturation from 0% to 100% in the seismic frequency band (1Hz-100Hz). Based on White’s model, three sandstone reservoir models are analyzed, which indicate different depositional environments. The modeling results verify that the frequency-dependent AVO attributes are sensitive to the partial saturation and their cross-plots can be used to distinguish the fluids saturation quantitatively.
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Reflection Coefficient Analysis Based on White Layered-patchy Saturation Model
Authors F. He, G.Z. Zhang, Z.L. Pei, J.J. Xue and J.J. SongSummaryAlthough significant advancement has occurred in the interpretation of seismic amplitude-variation-with-offset AVO anomalies, a theory is lacking to guide the interpretation of frequency-dependent seismic anomalies.This paper takes into account the mesoscopic fluid flow in the reservoir.And the reservoir is thought to be patchy-saturated dispersive medium, while the overlying shale is considered to be nondispersive medium.I derive a new expression of the incident-dependent reflection coefficient as a function of frequency at an interface between a nondispersive medium and a patchy-saturated dispersive medium, and analyze the variation of reflection coefficient with the incident angle and frequency under the condition of different combination of overlying shale and the reservoir. It suggests that the reflection is dependent on the viscoelastic characteristic difference between overlying shale and the reservoir, frequency and fluid flow in pores. Under the condition of different combination of overlying shale and the reservoir, the variation of reflection coefficient magnitude is divided into three AVOF classes.Also, AVO curve type is different with variable frequency.
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Dependency of AVO and AVOA Signature for long-offset P-wave Seismic Reflections in the Vicinity of Volcanic Structures
Authors M.A.A.M. Jelani and D. AngusSummaryIt is generally understood that imaging within the vicinity of the volcanic structures, such as the seaward dipping reflector (SDR) has been a difficult task. This is mainly due to the highly heterogeneous, systematic layering and stacking of basalts that has led to an effective transverse isotropic anisotropy within the SDR structure. Hence, wide-angle and wide-azimuth reflection seismic survey is one of the best techniques to use as it can record a lot more information compared to conventional reflection seismic surveys (e.g., greater offset and azimuthal measurements for travel-time differences and reflection amplitude variations). This is especially important for the identification of anisotropic features. In this paper, conceptual seismic models of the SDR geometry are created in order to analyse the variation of reflection coefficients with respect to different magnitudes and symmetries of fabric-induced anisotropy. Specifically, we seek to analyse whether the seismic amplitude response and critical reflections at dipping reflector show significant variations with azimuth with respect to the different top SDR horizon geometry. Based on our results, we conclude that azimuthal analysis of seismic amplitudes is influenced by the degree and type of anisotropy as well as by the geometry of the top and bottom horizon of reflector.
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Julia Application in Calculating Reflectivity from High Order Anisotropic Interface
Authors R. Malehmir and D. SchmittSummaryElastic anisotropy in the Earth causes many artifacts in an isotropic seismic processing and interpretation. To date, these issues have been ameliorated by using approximations to the full solutions for wave propagation and reflectivity for special material symmetries. This algorithm has been written to extend these capabilities to the general case of reflectivity from the interface between two anisotropic slabs of arbitrary symmetry and orientation. To achieve this, the algorithm solves for polarization, amplitude and slowness of all the wave modes generated by a plane wave incident to the interface. In the first step, the plane-wave velocities and polarizations of all three orthogonal wave modes are calculated for a given incidence angle. Second, the algorithm determines the reflection and transmission angles of all of the possible scattered modes followed by their respective velocities and polarization vectors. With this information, the algorithm solves system of equations incorporating the imposed boundary conditions to arrive at the scattered wave amplitudes. We have tested this algorithm in some of the most computationally difficult models to ensure there is no energy leakage in the system of calculations. This algorithm could be used in seismic processing, migration, and inversion of seismic data in anisotropic media.
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Nonlinear Three-term AVO Inversion Based on Exact Zoeppritz Equations
More LessSummaryObtaining interlayer weak reflection information that helps identify properties and accurate density information from complex and elusive reservoirs is particularly important for reservoir characterization and detection. However, conventional AVO inversion method is strongly influenced by the accuracy of the approximate Zoeppritz equations, which suppresses weak reflections coming from the commonly used prior distribution. In this abstract, we address these problems by using exact Zoeppritz equations. First, the inverse problem was constructed and the modified Cauchy distribution was introduced as the prior information by utilizing Bayes’ theorem. We then combined the idea of generalized linear inversion with Iterative Reweighed Least-Squares (IRLS) Algorithm to solve the problem. From the Zoeppritz equations, the complicated objective function was used for inversing the P- and S-wave velocities and density. The idea of GLI is used to solve the objective function, from which a nonlinear solution of the model parameters’ perturbations can be calculated. The IRLS Algorithm was applied to solve the nonlinear expression to obtain an updated iterative formula of the model parameters. Both synthetic and field data examples show that the new method can not only directly inverse P- and S-wave velocity and density, but also provides accurate estimation results, particularly for density.
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Azimuthal AVO of P-wave at the Boundary between Two TTI Media
More LessSummary3-D P-wave reflection coefficient between two weakly anisotropic TTI media is derived. The approximation is a function of azimuth, incidence, dip angles and anisotropic parameters. Expression is group into intercept, gradient and curvature just like Shuey-three terms, but there is a fourth item called disturbance, which is the function of the gamma, one of Thomsen parameters. The derived formula is not only consistent with the formula of VTI/HTI by Ruger, also demonstrates good accuracy.
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Downhole Microseismic Data Processing - Consistency of Locations, Source Mechanisms and Stress State
Authors Z. Jechumtálová, F. Chu, J. Rong, J. Procházka and L. EisnerSummaryWe present results of processing of microseismic events induced by hydraulic fracturing and detected by dual downhole monitoring arrays in nearly optimal geometry providing unique insight into hydraulic fracturing. We detected and located microseismic events, determined their magnitudes, source mechanisms and inverted stress field orientation. Event locations were forming a highly linear trend above the stimulated intervals. The source mechanisms were computed only for higher quality events which were detected on sufficient number of receivers to obtain reliable result. All detected source mechanisms were dip-slip mechanisms with a steep and nearly horizontal nodal plane. The source mechanisms represent shear events, non-double-couple components were very small consistent with the noise level in data and velocity model uncertainties. The strikes of inverted mechanisms corresponding to the nearly vertical fault plane are (within the error of the measurement) identical with the strike of the location trend. Finally, regional principal stress directions were inverted from the source mechanisms. The least principal stress σ3 is perpendicular to the strike of the trend of the locations, indicating that the hydraulic fracture propagated in the direction of maximum horizontal stress.
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Automatic Microseismic Events Detection by Phase-only Correlation
Authors C.X. Chang, W.S. Wu and W.Y. WangSummaryIdentification and detection of the microseismic events is significant issue in source locations and source mechanism analysis. And due to the large amount of microseismic records and need for rapid field analysis and monitoring, the automatic algorithms are more indispensable. In this study, we introduce an effective method for the identification and detecting of the microseismic events by judging if there is a P-wave phase in local segment from single three-component microseismic records. The new judging algorithm mainly contains following key steps: 1), transform the waveform time series into time-varying spectral representations; 2), detect the similarity of the frequency content in the time-frequency domain using the phase-only correlation function; 3), identify the P-phase by the combination analysis of three-component records. The proposed algorithm is compared to the traditional 1D crosscorrelation of the raw waveform, with a synthetic microseismic datasets and a real field-recorded datasets. The results show that the new algorithm is stable to distinguish the similar waveforms and dissimilar waveforms even for low SNR and emergent events, which is meaningful to select the microseismic events out of a large amount of records accurately and rapidly. It can be applied to some other geophysical analyses based on the waveform data.
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Microseismic Events Enhancement in Sensor Arrays Using Autocorrelation Based Filtering
Authors E. Liu, L. Zhu, J.H. McClellan, A. Al-Shuhail and S.I. KakaSummaryPassive microseismic data are commonly buried in noise, which presents a significant challenge in microseismic data analysis and event detection. In this work, we consider the situation where a sensor array provides multiple traces that each contain an arrival from the event, and propose an autocorrelation-based method that designs a denoising
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Investigation of Ambient Noise Levels in the Adana Basin and its Surroundings, Southern Turkey
Authors N. Bulut, A. Kocaoglu and A. KaslilarSummaryWe investigate the characteristics of background seismic noise levels in the Adana basin and its surroundings (Southern Turkey) by using seventeen broadband velocity seismometers operated by Kandilli Observatory Earthquake Research Institute (KOERI) of Bosphorus University and Earthquake Research Department (ERD) of Disaster and Emergency Management Presidency of Turkey. The probability density functions of power spectral densities are calculated and their mode values are mapped to observe the spatial variations in day and night times. We observe that the calculated noise levels are coherent in general with the low- and high-noise models of the Earth. We also show an example where noise levels change as a function of period in seasonal basis.
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Study of the Curvelet Transform for Aliasing 3D Seismic Data Recovery
More LessSummaryCurvelet transform has proven its effectiveness in image processing. In this paper a horizontal layer model with three layers was created and 3D seismic data was obtained through forward modelling. Then a comparative study was performed to test the ability of 2D and 3D curvelet transform for the reconstruction of the regularly or irregularly aliased 3D seismic data. It has been demonstrated that the missed 3D seismic data cannot be recovered by applying the 2D curvelet transform, but the 3D curvelet transform is able to reconstruct the full information based on the lateral information.
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Shaping Spectrum of Short-time Fourier Transform for Broadening the Seismic Bandwidth
More LessSummaryIncreasing seismic resolution is important for detecting more structural and stratigraphic detail. We propose a novel algorithm that combines the benefits of both the Fourier scaling theorem (FST) and the short-time Fourier transform (STFT) to obtain broader frequency bandwidth and thus improve the seismic resolution. In the proposed algorithm, the frequency spectrum in each window of the STFT is substituted by a weighted-stacking amplitude spectrum through the FST. We test the performance of the algorithm on synthetic and real data to obtain broader frequency spectrum without greatly boosting noise.
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A Robust Deconvolution Algorithm with Sparsity and Lateral Continuity Constraints
More LessSummarySparse deconvolution is a commonly used method in recent years. When the seismic data is clean, it can recover the reflectivity series perfectly. However, in the presence of noise, the algorithm can be unstable. To remedy this problem, we add a spatial constraint to the objective function. Thus, there are two kinds of prior information. One is within and the other is across the seismic traces. For the former, we use the modified Cauchy norm to suppress noise, and for the latter we use a prediction error filter (PEF) which is calculated through a t-x domain random noise reduction procedure to preserve the signal and enhance the coherence of seismic events across midpoints. The PEF is calculated from the noisy data and it should be recalculated from the denoised seismic data. The process of calculating signal, then getting a new PEF should be iterated a few times. The combination of time sparse and space continuous constraints provides multitrace solutions that are sparse in the vertical direction and continuous in the lateral direction. Synthetic data example demonstrates the robustness of our proposed method.
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Anelastic Medium Seismic Reflectivity Estimation With L1 Norm and Bregman Iteration
More LessSummaryIn anelastic medium, the seismic wavelet decays continuously as it propagates. We model the seismic traces with a nonstationary convolution model and estimate the reflectivity coefficients under the inversion framework. The reflectivity coefficients are usually sparse in time. To incorporate this a priori information, we choose L1 norm of the model parameter as the regularization term of the objective functional of the inverse problem. Bregman iterative algorithm is one of the most efficient and precise algorithms to solve this L1 norm based problem. The numerical experiments of synthetic traces and real stacked field data show the capability of the algorithm to solve the seismic reflectivity estimation problems with L1 norm model constraint.
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Colored Gabor Deconvolution
More LessSummaryGabor deconvolution achieves a non-stationary deconvolution operator that corrects for both wavelet shape and attenuation, which can improve the resolution of seismic data effectively. In this abstract, we proposed a new deconvolution approach for non-stationary seismic data using the colored Gabor deconvolution (CGD), which can achieve higher resolution by taking blue spectrum as the expected output. Variable-step sampling (VSS) which can resample the low-frequency area and subsample the high-frequency area is used to estimate the attenuation function reliably and improve the statistical efficiency. Synthetic and field examples show that the CGD can broaden the spectrum, improve the resolution of seismic data and make the reflection characteristics more reliable, which is more valuable in reservoir prediction.
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Coherent Noise Attenuation Using Mathematical Morphological Filtering
More LessSummaryCoherent noise attenuation is a troublesome problem in many seismic exploration areas. Traditional methods often utilize the differences in frequency, wave number or amplitude to separate signal and coherent noise. However, the application of the traditional methods is limited when the above differences between signal and coherent noise are too small to distinguish. For this reason, we try to seek a new method from the differences in the shape of seismic waves, and introduce the mathematical morphological filtering (MMF) into coherent noise attenuation. The morphological operation is along the trajectory of the coherent noise to implement the MMF. Application of this proposed method on synthetic and field seismic data demonstrates an excellent performance.
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Azimuthal Dependence of Normal Moveout Velocities in Anisotropic Media
Authors Y.V. Roganov and A. StovasSummaryWe derive equations for azimuthal dependence for NMO velocity in both group (depending on acquisition azimuth) domain and phase (depending on azimuth defined by the normal to incident and reflected plane waves) domains. Obtained equations are important do describe NMO velocities in vertical planes of traveltime surface and slowness surface. Derived equations are valid for single mode waves travelling in media with arbitrary anisotropic symmetry.
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Long-offset Moveout Approximation for VTI Elastic Layered Media
More LessSummaryThis study is an enhancement to existing moveout approximations in VTI layered media for large offsets. We suggest two new approximations that include five parameters. The first three parameters are conventional: zero-offset time, NMO velocity and quartic coefficient. The two additional parameters are related to large offsets. One of them describes nearly horizontal propagation in the fast layer of the overburden, while the other characterizes the remaining finite wave propagation distance and the finite traveltime across the slower velocity layers. Our approximations can be used with either a finite or an infinite offset match. In the case of an infinite match, the approximations converge to an exact theoretical asymptote. Another possibility is to establish the parameters of the approximation from a least squares fit within a given offset range, rather than for a specified offset point (either finite or infinite). Both new approximations match the exact ray tracing traveltime very well for P, P-SV and SH waves.
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Long-offset Parametric Moveout Approximation for VTI Elastic Layered Media
More LessSummaryThis study presents an enhancement to the existing parametric traveltime approximations in VTI elastic layered media by accounting for long-offset wave propagation in a more correct manner. The method is applicable for all types of pure-mode and converted waves, and it is highly accurate for all waves, except SV with strong anisotropy, dominated by cusps. We suggest a parametric approach where both the offset and the traveltime are functions of the horizontal slowness whose finite upper bound (critical slowness) corresponds to infinite offset and traveltime. We distinguish between the layer with the fastest horizontal velocity (“fast” layer) and the other (“slow”) layers. In vertically varying 1D layered media, the horizontal slowness is constant for all layers in both incident and reflected waves, for all wave types. Thus, for a power series approximation, the coefficients representing the contributions of the individual VTI layers to the total offset and traveltime can be summed. For nearly critical slowness, the contributions of the “fast” and “slow” layers are decoupled; this separation gives a better physical insight into the nature of longoffset wave propagation. The accuracy of the method is demonstrated by comparing the approximated offsets and traveltimes with numerical ray tracing.
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A NMO Correction Method Without Stretching Distortion
More LessSummaryThe conventional NMO correction method usually causes stretching distortion, especially in shallow layer and at large offset. This paper analyzed the reasons of stretching distortion and calculated the possible revising range of NMO correction values. Then corresponding updated NMO correction values can be obtained by adding the conventional NMO correction value to a series of equal-spaced correction values within the revising range. NMO correction without stretching distortion would be realized with the best NMO correction value chosen from all the updated values using cross-correlation method. Here we set the near-offset stacked trace after conventional NMO correction as a standard trace in the choosing of NMO updated correction value. Then selected a time window centering on each time sample and carried out NMO correction using each updated NMO correction value respectively, and calculated the cross-correlation of the data in the time window and that in standard trace, so the best NMO correction value is the updated one which corresponding to the largest cross-correlation value. The method can achieve NMO correction without stretching distortion in the case of crossing events in seismic data and has strong practicability. We proved its accuracy and effectiveness by model and practical data processing.
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Background Velocity Inversion with Scatter Gaussian Packet
More LessSummaryAccurate background velocity estimation is crucial to pre-stack depth migration and full waveform inversion. Traditionally, it is implemented in the image domain, such as the ray-based tomographic MVA and wave-equation MVA. Recently, reflection full waveform inversion method is presented, which aims to invert the background velocity model with reflection waves. Inspired by the reflection wave inversion method, we present a Gaussian packet reflection traveltime inversion theory. The scatterer is calculated using scatter Gaussian packet firstly. Then the reflection waves are simulated with scatter Gaussian packet, too. With the observed and simulated scatter waves, the objective function is defined as the L2 norm of traveltime residual. Instead of calculating the partial derivative of objective function with respect to background model, the gradient of the objective function is expressed by the total derivative. Compared with the reflection tomography using wave equation, Gaussian packet inversion shows advantages of higher efficiency and better flexibility.
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Velocity Model Building with Well Mis-tie Extension in TTI Media
More LessSummaryWe discuss a TTI velocity model building approach that utilizes the well mis-tie information as inversion constraints. Since the well mis-tie information is available only at sparse locations, we introduce a bridging function to extend laterally the mis-ties information to its surroundings according to the local geologic structures. The resulting inversion scheme has the advantage of mitigating the illconditioning of the inversion operator and hence improves the robustness of the solution. We elaborate in detail this approach in this abstract and demonstrate with a real data example that the proposed method has both improved the positioning of depth migrated image and simultaneously enhanced the flatness of common image gathers.
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First-arrival Traveltime Tomography with Modified Total Variation Regularization
More LessSummaryThe first-arrival traveltime tomography is a robust tool for near-surface velocity estimation. A common approach to stabilize the ill-posed inverse problem is to apply Tikhonov regularization to the inversion. However, the Tikhonov regularization method recovers smooth local structures while blurring the sharp features in the model solution. We present a first-arrival traveltime tomography method with modified total variation regularization to preserve sharp velocity contrasts and improve the accuracy of velocity inversion. In order to solve the minimization problem of the new traveltime inversion method, we decouple the original optimization problem into two subproblems: a standard traveltime inversion problem with the traditional Tikhonov regularization and a L2 total variation problem. We use conjugate gradient method and split-Bregman iterative method to solve these two subproblems, respectively. Our synthetic and field data examples show that the new method produces higher resolution models than the Tikhonov method for the models with sharp interfaces.
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Estimation of the Anisotropy Parameters from Imaging Moveout of Diving Wave in a Factorized VTI Medium
Authors S. Xu, A. Stovas and T. AlkhalifahSummaryThe importance of diving waves is being realized since they provide long model wavelength information, which can be utilized to invert the reflection wave information in a full waveform inversion (FWI). The factorized model is defined as a combination of vertical heterogeneity and constant anisotropy, and we define the closed form description of the diving wave traveltime. We propose analytical approximation for residual imaging moveout of diving waves in a factorized anisotropic medium. By using the classical semblance analysis, we estimate the optimal anisotropic parameters that can be later used for FWI initial model building.
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Quantifying and Updating Facies Uncertainties Using ES-MDA - Real Field Case Study
Authors R.G. Hanea, T. Ek, B. Massart and C. PettanSummaryWe implemented the Adaptive Plurigaussian Simulation method under the Fast Model Update framework on a real field case, utilizing the Ensemble Smoother Multiple Data Assimilation method for assisted history matching. The exercise we present shows that updating facies realizations on a grid by grid level, allows controlling or avoiding the stochastic variations that could lead to a significant spread in reservoir pressure behavior and the fluid flows.
The implementation brought to the asset team new history matching opportunities and also a robust tool for reservoir understanding. It has a direct impact on several reservoir management activities, like detailed well planning, production forecast and drainage strategy optimization, where the reservoir simulation models are broadly used.
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Chance of Maturation - An Approach for Resource Classification and Portfolio Management
More LessSummaryThe baseline value of an oil and gas producing company is the volumes carried in the portfolio and the associated value of its hydrocarbon resources. Such a portfolio carries considerable risks that these resources are produced at all. Besides these risks, uncertainties exist. Risk and uncertainty are related, but are different aspects of expectation.
Although, international resource classification systems like SEC (Reserves only), SPE-PRMS (Reserves, Contingent Resources, Prospective Resources) and UNFC 2009 (E-F-G-Axis, resource cube) mention project maturity and development risks, there is no guidance to risk assessment. A quantitative estimate of the chance to get a project into the producing status is not available.
While for Exploration projects evaluation a standardised concept to estimate Pg and Pc is established, a standardised quantitative risk (1-chance) assessment covering (re-)development project risks is not commonly available.
This paper aims to describe a methodology to establish a project based quantitative risk assessment by introducing the Chance of Maturation CoM concept.
The CoM concept is used in portfolio management and aggregation of projects with different risk profiles, mapping of reserves/resource classification to international standards, aggregated production forecasting and its associated probability to achieve certain targets. The CoM makes the risks transparent and projects comparable.
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Application of Multiple 3D Static Model Scenarios in a Complex Carbonate Reservoir for Accurate Production Forecasting
Authors A. Gryaznov, I. Martin, A. Kshirsagar and V. Dos SantosSummaryThe need for a consistent and accurate production forecast is of upmost importance in field development planning and even more so in times of a challenging oil price. Results are also required in an ever shortening timeframe; however accurate simulation and forecasting can only be achieved using accurate 3D static models. The fundamental task is not only to create and simulate just one model version but use a variety of 3D models to get a range of results, e.g. low, middle and high cases (P90-P50-P10). Uncertainty analysis can be used to get a range of many equiprobable stochastic model realisations, from which we can choose the low to high cases. However, this approach if not tested and calibrated correctly, could lead to model versions that do not represent a realistic geological description of a reservoir. For this purpose, a more beneficial approach is to create several alternative model versions, based on geological concepts, upscaling methods, input data and decisions or variations applied in the static modelling workflow. The results are a number of models which give a consistent range of hydrocarbon production profiles allowing the assessment of the potential of the reservoir and quantification of the reservoir uncertainties and challenges
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New High Risk Deep Opportunities in a Mature Field, Desfiladero Bayo, Mendoza, Argentina
Authors F. Mora, S. Espinach, S. Koch, G. Ballester and M. VarasSummaryDesfiladero Bayo is an oil field located in western Argentina, on the border between two states, Neuquén and Mendoza. It was discovered in 1972 and its development began in 1983. At the present, the field has a complete development history (primary, secondary and tertiary recovery). In this area, the productive reservoirs are shallow, and its main production mechanism is waterflooding sweep.
In recent years, multidisciplinary studies had been carried out with focus on optimizing secondary recovery, opening new layers of low interest, assess edge zones, infill drilling wells, and a tertiary recovery pilot in a conceptualization phase to evaluate this technology in the area.
As a part of an integrated development plan, new opportunities in a mature field were evaluated through multidisciplinary studies to extend the production horizon of the field adding deep reservoirs to the field development plan.
The integration of new opportunities, characterized by deep reservoirs, in a project with a small level of uncertainty represents a significant challenge to the reservoir management plan implemented in Desfiladero Bayo.
Uncertainties were handled through a methodology that included probability analysis and decision trees, simplifying the decision making process and the selection of different options for new data collection within the integrated development plan.
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CO2 Flooding Seismic Monitoring of Reservoir Based on Frequency-dependent Velocity Factor
Authors W. Xiao, J.H. Zhang, J. Li, M.Y. Tan and S.L. CuiSummaryFrequency-dependent phenomenon and amplitude attenuation can be caused by CO2 injection, so we can utilize frequency-dependent velocity factor to monitor the dynamic characteristic of reservoir. In this paper, we deduce the quantitative form of frequency-dependent factors based on convolution model and establish inversion equation containing frequency-dependent velocity factors. In order to verify the feasibility of proposed method, we generate the synthetic gathers utilizing forward modelling method in viscoelastic medium to simulate the dispersion and attenuation caused by CO2 injection. All synthetic tests illustrate the feasibility of our method and establish a solid foundation for the field application. Furthermore, we apply our method to oil displacement monitoring based on seismic data before and after CO2 injection in G89 well block of Sheng-li oilfield located in the east of China, the frequency-dependent factors show high-value anomaly at the well block after CO2 injection. The application on this field case shows that frequency-dependent factors in our work can detect anomaly of reservoir before and after CO2 injection effectively and predict the influence scope of CO2 flooding.
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New Methodology to Calculate Water Cut in Mature Waterflood - Alba Field
Authors B. Dujardin and I. MooreSummaryIn a mature waterflood, understanding individual well performance is critical to optimize production and operate efficiently. Specifically, accuracy on watercut measurement is one of the most important reservoir management challenges and becomes even more important with time and increasing watercut. Traditionally offshore operators monitor individual wells to estimate watercut with flowline fluid samples, with two-phase separator well test data and with more complex methods such as watercut and multiphase meters when available. At Alba a new methodology based on a better understanding of gas production was derived to calculate more accurately watercut from gas and liquid measurements; it was then successfully applied to calculate watercut during individual well tests. This new approach is more accurate and reliable than traditional methods to estimate watercut. Used on some wells with high uncertainty on watercut, it revealed for the first time the performance of these wells. Deployment of this method to all Alba wells was simple because it did not require any investment and all the data was already available. This new information has already added significant value to Alba by supporting key reservoir management decisions such as slot recovery, workover opportunities, redrill and for optimizing production by shutting-in high watercut wells.
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Making Full Use of Horizontal Well Data in Depth Conversion - A Case Study at the Dan Field
Authors A.K. Lundsgaard, N. Hodgson and C.E. DererSummaryIn this abstract we give a case study of a depth conversion that takes full advantage of horizontal well data and the uncertainty on the well track. By allowing wells path to be simultaneously optimized with other uncertain data we can identify mispositioned wells, by examining the amount that a well path needs been moved to make them consistent with the surrounding data. This knowledge can be used by the geologist to quickly screen for the most problematic wells. Ultimately this provides depth surfaces that are consistent with the all well data, especially zone information along long horizontal wells, which serves as a good starting position for subsequent geomodelling tasks.4
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Scalability and Performance Efficiency of History Matching Workflows using MCMC and Adjoint Techniques Applied to the Norne North Sea Reservoir Case Study
Authors Ralf Schulze-Riegert, Michael Nwakile, Sergey Skripkin and Yannick WillenSummaryAn increasing number of field development projects include rigorous uncertainty quantification workflows based on parameterized subsurface uncertainties. Reservoir model calibration workflows for reservoir simulation models including historical production data, also called history matching, deliver non-unique solutions and remain technically challenging. In addition, the validation process of the reservoir simulation model often introduces a break of the conceptual connection to the geological model. This raises questions on how to quantify the deviation between the calibrated simulation model and the original geological model.
Workflow designs for history matching require scalable and efficient optimization techniques to address project needs. Derivative-free techniques like Markov Chain Monte Carlo (MCMC) are used for optimization and uncertainty quantification. Adjoint techniques derive analytical sensitivities directly from the flow equations. For history matching those sensitivities are efficiently used for property updates on grid block level. Both techniques have different characteristics and support alternative history matching strategies like global vs. local, stochastic vs. deterministic.
In this work both techniques will be applied in an integrated workflow design to the Norne field. The Norne field is a North Sea oil-and-gas reservoir with approximately 30 wells, with one third being used for WAG injection for pressure support. Field data was previously released by Statoil and made available for a public benchmark study (NTNU Norway) testing history matching techniques including production and time-lapsed seismic data.
We focus on well production data for history matching. MCMC is used for global parameter updates and uncertainty quantification in a Bayesian context. An implementation of an adjoint technique is applied for analytical sensitivity calculations and local parameter adjustments of rock properties. History matching results are presented for field wide and well-by-well production data. Consistency checks between updated and original geological model are presented for rock property distribution maps. Geostatistical measures including spatial correlations are used to quantify deviations between updated and original geological model. In conclusion scalability and performance efficiency of the practical workflow implementation is discussed with a perspective of a consistent feedback loop from history matching to geological modeling.
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Identification of the Compositional Path Followed During Reservoir Simulation Improves the Accuracy and Accelerates the Phase Behavior Calculations
Authors Vassilis Gaganis, Nikos Varotsis and Steve TodmanSummaryFor depletion-drive reservoirs, which constitute the vast majority of the running projects, many operators still use black-oil simulation to speed up calculations during which the PVT values are obtained from prior defined Black Oil Tables (BOT). These Tables are generated a) by use of correlations, b) by transforming computationally the Differential Vaporization (DV) laboratory data to take into account the transfer of fluids from the reservoir to surface via the so called Composite Vaporization path (CV) thus emulating the Composite Differential Vaporization (DVC) process or c) are produced by using tuned EoS models simulating the DVC as it is widely believed that the differential liberation path represents more closely the variation of the reservoir gas and liquid phase compositions within the reservoir during pressure decline. When the dependence of equilibrium k-values with composition becomes significant, compositional simulation is required and an EoS model is used to provide phase behavior. In that case, the solution of the phase behavior problem during simulation runs consumes a considerable part of the total CPU time required accounting up to 70% for Implicit Pressure Explicit Concentration (IMPEC) realizations. In fact, for solving the non-linear problem, the EoS based phase equilibrium computations usually need to be repeated two to four times per grid block and time step, depending on the timestep size and the proximity of the reservoir conditions to the critical ones, to achieve convergence of the Newton-Raphson algorithm. In this work, the application of the different approaches for generating BOT for oils are reviewed and guidelines are issued for different type of fluids. Several reservoir simulation runs were conducted using a 3-component synthetic oil, a volatile and a near critical oil and the compositional path that is followed by the equilibrium oil and gas phases was monitored both spatially and timewise. It is shown that down to relatively low pressures this path follows very closely that of the Constant Composition Expansion (CCE) study although at pressures close to the abandonment one it might shift slightly towards the DV path. As a consequence, the reservoir equilibrium phases at each cell were found to exhibit PVT values very close to those obtained by flashing the equilibrium phases produced from the CCE path to the surface separation conditions (CCES). Only at low pressures the volumetric factors exhibit an increased variance and are shown to lie between the values obtained from CCES and DVC. Moreover, the PVT values of the equilibrium phases of the reservoir fluids obtained from the simulations were compared to those obtained either by traditional DV-to-CV converting methods (such as those of Dake and McCain) or by established correlations.
The above findings render the selection of the CCE compositional path as the most suitable one for generating BOTs. They also demonstrate that the compositions encountered during a compositional simulation run can be described by a limited set of tie-lines, thus increasing the confidence in the utilization of promising phase behavior accelerating methods such as k-value generating models and the Tie-Line Tabulation approach (CSAT).
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Reservoir Model Selection for Dynamic Simulation
Authors J.H. de Kok and W.J. van StrienSummaryThis extended abstract presents a pragmatic approach to select reservoir models for dynamic simulation. The method ensures dynamic information to be used at an early stage of static model construction, avoiding unnecessary iteration loops at a later stage. It also takes advantage of investigating a large search space and encourages the integrated team to think about development options at an early stage of the dynamic simulation process. Throughout the process the goal is to limit the amount of models carried into the next modeling or simulation phases while maintaining the range of possible outcomes and maximize the understanding of the reservoir. The abstract contains several examples and ideas on how to make best use of this approach.
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The Potential for Predicting Production by Characterizing Fluid Flow and Drainage Patterns Using Microseismicity
Authors T.I. Urbancic, L. Smith-Boughner, A.M. Baig, E. von Lunen, J. Budge and J. HendrickSummaryWe apply a continuum approach to describe the dynamics of seismicity observed during a hydraulic fracture of a multiple horizontal well pad. By exploiting the multi-well observation geometry, we are able to resolve the seismic moment tensors of the high-quality events. Not only does this information constrain the fracture orientations, but it can be used to reconstruct the state of stress/strain in the reservoir. We use the strain to drainage of the reservoir through a strain-flow analysis. Furthermore we examine the spatial and temporal variations in the microseismicity, as well as the energy release characteristics, to image the regions of the reservoir where plastic damage is most confined around the wellbores. To validate both approaches we use PLT data.
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A Novel Approach for Waterflood Management Optimisation using Streamline Technology
Authors X. Li, T. Yi, M. Giddins, S. Krevor and S. AderemiSummaryThis paper presents a new streamline-based workflow to cover the two main aspects of waterflood management optimisation: infill drilling well location identification and injection rate allocation. Streamline properties are used in every step of the evaluation and decision-making process in the workflow. A novel ranking scheme, weighted by streamline ‘remaining mobile oil in pattern’, is developed in this study. The well ranking criteria are not only based on the properties of individual well completion cells as in a traditional quality map, but also account for connectivity between injector/producer pairs. In such a way, candidate producers at high-quality map locations, but with poor connectivity or limited swept area, can be screened out. The other main component of the workflow is to perform dynamic pattern injection reallocation in response to the changed well pattern resulting from newly introduced producers. A unique insight for utilization of a multi-zone waterflood for a vertically heterogeneous field is also provided.
2D and 3D heterogeneous models were used to develop and validate the workflow for its general implementation on real field models. The final oil recovery and net present value (NPV) analysis show that the oil recovery can be increased significantly compared to traditional optimisation methods.
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Joint Optimization of Well Locations and Operational Conditions Using a New Hybrid Algorithm
More LessSummarySince optimal well locations and operational conditions are dependent on each other, these variables have been recently optimized together. Particle swarm optimization (PSO) algorithm is a global optimization method, which is computationally less attractive. Ensemble based optimization (EnOpt) method is a gradient based optimization method, which converges fast but is susceptible to get trapped into a local optima. In this paper, we propose a new hybrid algorithm PSO-EnOpt for the joint optimization problem. By combining PSO and EnOpt algorithms, PSO-EnOpt can take the advantages of the both algorithms. In the PSO-EnOpt algorithm, PSO locates the optimizing vector near global optima. Then, EnOpt finds a global solution with fast converge rates. Therefore, PSO-EnOpt can have faster converge rates compare to the PSO algorithm. Also, it can provide more stable results than EnOpt algorithm due to the global search ability of PSO. We apply the proposed algorithm to determine an optimal injection well location, injection rates, and producing bottomhole pressures. PSO-EnOpt shows superior performance compare to other preexisting algorithms. The proposed algorithm can be applicable to real field development problems and help decision makers to make rapid and optimal decisions.
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Experimental Validation of a Pore-scale Derived Dimensionless Capillary Pressure Function for Imbibition under Mixed Wet Conditions
Authors Y. Zhou, J. Helland, D. Hatzignatiou, R. Ahsan and A. HiorthSummaryIn this work, we validate experimentally a dimensionless capillary pressure function for imbibition at mixed-wet conditionsthat we developed recently based on pore-scale modeling in rock images. The difference to Leverett’s traditional J-function is that our dimensionless function accounts for wettability and initial water saturation after primary drainage through area-averaged, effective contact angles that depend on the wetting property and distribution of oil- and water-wet grain surfaces. We hypothesized that describing these effective contact angles as a function of Amott wettability index relates the pore- and core-scale wettability, and that pore-scale imbibition simulations can provide these relations for specific rocks. In the present work, we adopt the dimensionless function to scale imbibition capillary pressure data measured on mixed-wet sandstone and chalk cores. The measured data practically collapse to a unique curve when subjected to the dimensionless capillary pressure function. For each rock material, we employ the average, dimensionless curve to reproduce the measured capillary pressure curves and obtain excellent agreement. We also demonstrate two approaches to generate different capillary pressure curves at other mixed-wettability states than that available from the data used to generate the dimensionless curve. The first approach changes the shape of the spontaneous- and forced-imbibition segments of the capillary pressure curve while the saturation at zero capillary pressure is constant. The second approach shifts the vertical level of the entire capillary pressure curve, such that the Amott wetting index (and the saturation at zero capillary pressure) changes accordingly. Thus, integrating these two approaches with the dimensionless function yields increased flexibility to account for different mixed-wettability states. The validated dimensionless function scales mixed-wet capillary pressure curves from core samples accurately, which demonstrates its applicability to describe variations of wettability and permeability with capillary pressure in reservoir simulation models. This allows for improved utilization of core experiments in predicting reservoir performance. Reservoir simulation models can also employ the dimensionless function together with existing capillary pressure correlations.
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Insights of Berea Sandstone Wettability Alteration as A-model of Sandstone Reservoir through Contact Angle Measurement
Authors R. Kareem, P. Cubillas, H. J. Riggs, J. Gluyas, D.R. Gröcke and H.C. GreenwellSummaryEnhanced oil recovery (EOR) methods target the residual ca. 50 % of crude oil, found coating the pore surfaces of sandstone reservoirs. Low salinity water flooding EOR involves the injection of waters with low salt concentrations into the reservoir. These methods, through a contested mechanism, alter the wettability of the reservoir rock and promote oil displacement. In this work, we have used environmental scanning electron microscopy (ESEM) to measure and assess the change in wettability on oil-treated detrital quartz grains from Berea sandstone and model single-crystal high-quality quartz. Crude oil, as well as a “model-oil” (decanoic acid) where used. Wettability alteration was brought by flushing the pre-treated crystals with low concentration brines (0.01M) of different composition (NaCl, CaCl2, MgCl2, and KCl). Results show that, in the case of quartz surfaces from Berea sandstone, NaCl has the greater effect in changing the wettability state from oil wet to water wet. Results are noticeably aligned with total organic carbon (TOC) data. In contrast, the model-quartz crystals do not show great changes in wettability. The variation in results is probably due to the influence of nano-mineral coatings in the sandstone’s quartz crystals, as observed by high-resolution SEM. These results also highlight the importance of using natural mineral surfaces in the EOR study.
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Optimizing the Low Salinity Water for EOR Effects in Sandstone Reservoirs - Composition vs Salinity
Authors I.D. Piñerez Torrijos, T. Puntervold, S. Strand and A. RezaeidoustSummaryParticularly, even though a low salinity brine often is a successful EOR fluid, this paper shows that the importance of specific salinity comes along with the brine composition. Water with salinities below 5000 ppm are generally accepted as LS EOR fluids, but in this work “smart water” EOR effects at higher salinities than 5000 ppm have been observed. Improved oil recovery was observed in tertiary mode using a 40000 ppm NaCl brine and 25000 ppm NaCl brine, the results are in line with the suggested chemical mechanism for wettability alteration due to a local pH increase triggered by calcium desorption. The speed of oil production and ultimate recovery is influenced by the concentration of Ca2+ in the FW and salinity (presence of NaCl) of the smart water brine.
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Geochemical Interpretation and Field Scale Optimization of Low Salinity Water flooding
Authors Ngoc T. B. Nguyen, Cuong T. Q. Dang, Long X. Nghiem and Zhangxin ChenSummaryLow Salinity Waterflooding (LSW) is an emerging Enhanced Oil Recovery (EOR) method. Wettability alteration towards increased water wetness in LSW is the widely accepted mechanism for the enhanced oil recovery. This phenomenon can physically be explained by ionic exchanges and geochemical reactions. However, the detailed ion exchanges have never been adequately addressed, and the explanations provided in the literature are sometimes contradictory leading to challenges of a successful LSW design. This paper aims to: (1) present detailed ion exchanges and geochemical reactions that happen in LSW using a compositional simulator; (2) analyze the key factors that affect an ion exchange process and address how to maximize the preferable wettability alteration; (3) investigate the potential of combining CO2 with LSW (CO2 LSWAG) to promote geochemical reactions and maximize the final oil recovery factor; (4) conduct a robust optimization of CO2 LSWAG under geological uncertainties.
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Understanding the Chemical Mechanisms for Low Salinity Waterflooding
Authors Changhe Qiao, Russell Johns and Li LiSummaryLow salinity water (LSW) is reported to improve oil recovery (IOR) significantly in sandstone and carbonate core experiments. The IOR is because of the specific composition of the injection water, in particular the concentrations of SO42-, Ca2+, and Mg2+. Ranges of IOR vary significantly depending on the brine, oil and cores used. We previously developed a process-based and predictive model that explicitly includes the chemical interactions between crude oil, brine, and the carbonate surface that alter rock wettability. In this research, we use the developed model to optimize the IOR considering the brine, oil and mineral compositions.
The wettability alteration is predicted by the relative change of the surface adsorbed carboxylic acids, which is coupled with a set of aqueous and surface reactions. The total concentrations of aqueous and surface species are varied individually and together over a large range while precipitation and dissolution reactions are also included. The wettability is mapped in the space spanned by the species concentrations.
The IOR depend strongly on the concentration of Ca2+, Mg2+ and SO42-, as well as the total ionic strength. CaSO4 and MgSO4 precipitation are found to reduce the extent of the wettability alteration to a more water wet state. Ca2+ and Mg2+ can replace each other at low concentration, while less Ca2+ and more Mg2+ leads to more wettability alteration because MgSO4 has a higher solubility in water than CaSO4. The injection water “recipes” that maximize IOR depends strongly on a suite of reservoir properties, including the initial formation water, and available water source, as well as the reservoir mineralogy and crude oil composition. Our results demonstrate for specific cases how to select the best injection water chemistry to maximize oil wettability alteration.
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Integrated Modeling for Assisted History Matching and Production Forecasting of Low Salinity Waterflooding
Authors Cuong Dang, Long Nghiem, Ngoc Nguyen, Zhangxing Chen and Chaodong YangSummaryFrom a technical point of view, the success or failure of LSW (low salinity waterflooding) projects strongly depends on reservoir geology; however, this has not been systematically evaluated in the past and the effects of clay minerals are often neglected in conventional reservoir simulation. This paper presents one of the first studies on integrated modeling, assisted history matching (HM) and production forecasting of field-scale LSW.
To handle this complex recovery process, we used a comprehensive ion-exchange model, fully coupled with geochemistry specially designed for the modeling of LSW physical phenomena in an EOS reservoir simulator. The model is capable of accounting for the critical role of the properties, quantity, and distributions of clay minerals. We developed an integrated modeling approach that involves the combination of geological software, a reservoir simulator, and a robust optimizer in a big-loop workflow for sensitivity analysis, HM, optimization, and uncertainty assessment. The numerical simulation results indicate that LSW’s performance depends critically on the reservoir geological characteristics. Multiple geological realizations can be automatically generated from the big-loop approach that are needed for fast and accurate HM and optimization of LSW. In sandstone reservoirs, clay content varies across regions, resulting in differences in ion-exchange capacity and weights of the relative permeability modification. We introduce the scaled-equivalent-fraction ion exchange which is associated with the calculated Cation-Exchange-Capacity function; the wettability alteration will be shifted based on both the ion exchange and the clay content in each grid block.
The key parameters for successful field-scale LSW HM include: clay distribution/quantity associated with different facies, relative permeability modification, wettability alteration thresholds, reservoir minerals, geochemical reactions, and operating conditions. Finally, LSW HM by tuning reservoir parameters only may lead to poor prediction results, while the integrated modeling approach provides much better forecasting results to the true history data.
The work presented in this paper contributes to an understanding of the critical roles of reservoir geology on the field-scale LSW performance, in particular, for substantially reducing HM errors, accurately predicting the future production, maximizing oil recovery and minimizing the risks of LSW implementation.
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Effects of Injection Rate of Low Salinity Brine on Oil Recovery Mechanisms and Relative Permeability Curves
Authors F. Srisuriyachai, S. Panthuvichien, T. Phomsuwansiri and W. KatekaewSummaryLow Salinity Brine (LSB) injection has been widely studied and several oil recovery mechanisms are proposed. Implementation of LSB injection does not yield only benefit from physical displacement as obtained from conventional waterflooding, it also provides displacement from chemical process. However, both displacement mechanisms might not occur at the same time. Physical displacement occurs immediately once water is injected into formation but chemical displacement might require time to increase retention of potential ions onto rock surface. Injection rate of LSB is therefore, considered as a key parameter to maximize oil recovery from this technique. From the study, moderate injection rate yields benefit from both displacements mechanisms and as a consequence, the highest oil recovery factor is obtained. Small injection rate favors only chemical displacement mechanism, whereas part of oil is remained untouched in case of high injection rate. Unsteady state relative permeability curves are constructed and they are good evidences to explain oil recovery mechanisms from different injection rates. Great reduction of relative permeability to water at residual oil saturation suggests that chemical process is favorable at lower injection rates.
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Modelling of Geochemical Reactions During Smart Water Injection in Carbonate Reservoirs
More LessSummaryExtensive studies have confirmed that altering ionic composition of injection water has a big impact on the ultimate oil recovery. Different mechanisms have been proposed to explain the positive effects of Smart Water injection, but no single one is universally accepted as the dominant mechanism. Therefore, in the paper, we conduct a three-dimensional reactive transport modelling study to investigate the geochemical processes during seawater flooding altering seawater with different sulphate concentrations injected into a carbonate reservoir which can help the understanding of the possible mechanism behind Smart Water injection. A series of calcite and anhydrite mineral reactions are key in situ chemical reactions in the study. At the early stage, CO2 partitioning from the hydrocarbon phase into the brine causes significant calcite dissolution. This process can be enhanced by increasing sulphate concentration in the injection water. Sulphate concentration in the injection has a significant impact on whether the calcite is continuously dissolved or not after the CO2 front passes. In the modelling cases that include thermal transport, reservoir temperature is cooled by injection water, and thus anhydrite precipitation and calcite dissolution are decreased.
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Identifying Unconventional Potential Using Seismic Inversion and Neural Networks - An Eagle Ford Shale Study
Authors X.E. Refunjol, L. Infante and A. BernaezSummaryUsing simultaneous inversion and neural networks of log and core data to generate impedance, porosity, and TOC volumes, we are able to study the behavior of reservoir qualities laterally and vertically. We conclude that high-grading of assets can be achieved by identifying and ultimately developing areas of coinciding favorable impedance, porosity, and TOC properties. Areas for favorable well stimulation placement and improved hydrocarbon recovery can also be identified. Further, this methodology can serve to illuminate non favorable areas, serving as a risk assessment methodology as a well planning tool.
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