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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
901 - 920 of 980 results
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High Resolution Reflection Separation Method for Dipole Acoustic Logging
More LessSummaryTo image the formation structure outside the borehole with reflected wave of dipole acoustic logging has attracted widespread attentions in recent years in the area of heterogeneous reservoir evaluation, due to its directivity and deep detecting depth. To obtain the reflected wave from the whole waveform of dipole acoustic logging, a new reflection separation method based on high resolution Radon transform is developed to adapt to the borehole environment. Instead of using the least square method, which can cause trails in Radon domain, the high resolution method is employed for its ability to make the different wave field focus in the Radon domain respectively. Moreover, through combining the principles of maximum entropy and Bayesian, the high resolution can be achieved. The processing results of simulation data show that the new method can be used to extract the desired wave field under complicated situations. Compared to the least square method and the F-K filtering, high resolution Radon transform can make the direct wave strongly focused into an approximate point within the Radon domain, which makes it easier to extract reflection. Finally, applications of field data to separate reflection were implemented to further verify the validity and accuracy of this method.
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Automatic Drift Time Estimation
By TC CuiSummaryThe drift time is the difference in traveltime at the seismic frequency and the sonic logging frequency in anelastic media. The stationary synthetic seismogram needs drift time correction to tie the nonstationary seismic trace. Without knowledge of Q or a check-shot survey, dynamic time warping can estimate the drift time associated with apparent Q automatically by matching the stationary and nonstationary seismograms. After applying drift time correction to the stationary seismogram, the residual constant-phase between it and the nonstationary seismogram is small and almost constant with traveltime. The final crosscorrelation coefficient of stationary and nonstationary seismograms can be as high as 0.95.
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Flow through Experiment on CO2-brine-rock Interaction in a Sandstone from the Altmark Gas Reservoir
Authors F. Huq, S.B. Haderlein, O.A. Cirpka, M. Nowak, P. Blum and P. GrathwohlSummaryWe performed flow through experiments to study the water-rock interactions caused by CO2 injection in sandstones obtained from the Altmark natural gas reservoir under reservoir conditions of 125°C and 50 bar CO2 partial pressure. CO2-saturated brine (41.62 g/ L NaCl and 31.98 g/L CaCl2•2H2O), mimicking the chemical composition of the formation water, was used as an injection solution. The major components in the sandstone were quartz (clasts + cement), feldspars, clay minerals (illite and chlorite), and anhydrite, the latter present mostly as cement. Trace amounts of carbonate and barite cements were also present. Fluid analysis suggested the predominant dissolution of anhydrite causing increased concentrations of sulfate at early time periods. Dissolution of feldspar, barite and minor amounts of clay (illite + chlorite) was also evident during the flow-through experiment. Geochemical modeling does not predict secondary mineral precipitation under these conditions. The experimental data could be used for numerical simulations predicting CO2 storage during injection in sandstone reservoirs.
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CO2-rock Interaction on the Example of Permian Sedimentary Rocks
More LessSummaryDepleted hydrocarbon (oil and gas) reservoirs in Poland are regarded for underground storage of carbon dioxide. The deposits potentially usable for CO2 sequestration ale located within Permian sandstones and partially carbonate rocks.
The purpose of the paper is to present some aspects of CO2 – rock interaction, on the example of Permian sedimentary rocks occurring in the Polish Basin, regarding possible acid gas storage.
The composed samples of rock and wellbore cement were exposed to CO2-saturated brine, in the autoclave reactor, under the formation conditions. The samples were analyzed before and after reactor experiments to report mineralogical and textural changes. The most significant alteration appears after the third stage of the experiment, with duration of 200 days. The observed changes are differentiated and dependent on the lithology. In case of carbonate rocks (limestone and dolomite) the changes are limited to the local dissolution of CaCO3, and secondary precipitation of this phase. In case of anhydrite and sandstone the significant increase of porosity in outer zone of the samples was noted. In a process of CO2 sequestration the pores and fissures formed in rocks can be a potential migration path for gases, especially on the rock-cement interface.
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Study of Shale Wettability for CO2 Storage
Authors N. Shojai Kaveh, A. Barnhoorn, F.C. Schoemaker and K.H.A.A. WolfSummaryFor a water-saturated cap-rock, which consists of a low-permeability porous material, the wettability of the reservoir rock-connate water- CO2 system and the interfacial tension (IFT) between CO2 and connate water are the significant parameters for the evaluation of the capillary sealing. Also, the amount of capillary-trapped CO2 depends on the wettability of reservoir rocks. The wettability of the rock matrix has a strong effect on the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. In this work, the equilibrium contact angles of water/shale system were determined with CO2 for a wide range of pressures at a constant temperature of 318 K by using the dynamic captive bubble method. The results reveal that intermediate-wet conditions and hence possible leakage of CO2 must to be considered at relatively high pressures, however, the salt concentration of the water in the shales plays an important role too. The results show that this estimate is highly dependent on the pore structure, fluid composition and pressure/temperature conditions of the reservoirs. These properties need to be first evaluated before estimates for shale capillarity is used.
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Investigating the Potential of Saline Aquifers for CO2 Mineral Storage - PHREEQC Batch −1D Diffusion-reaction Simulations
Authors S.M. Seyyedi Nasooh Abad and M. PasdarSummaryDue to increase in CO2 concentration in the atmosphere and its consequent problems, finding a solution for reducing CO2 concentration in the atmosphere is very important. One promising method that has been proposed for reducing the substantial amount of CO2, released to atmosphere, is sequestration of CO2 in saline aquifers. Having injected CO2 into a saline aquifer, it starts dissolving into the brine and it forms a weak carbonic acid. Over a long time, however, this weak acid can react with the minerals in the surrounding rock to form solid minerals. This process is one of the safest mechanisms for CO2 storage in saline aquifers; however, it can be rapid or very slow.
In this study based on the XRD results of a reservoir core, we assess the potential of that reservoir for CO2 mineral storage by tracking the precipitation and dissolution of each mineral over 100 years. We simulated the aquifer system at reservoir pressure by using PHREEQC. For this purpose, we used a closed-system batch simulation at constant CO2 pressure of 454 atm with sensitivity studies of temperature. Next, we estimated the change in porosity caused by mineral reactions.
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Analytical Solution for the Effect of Kv/Kh on Plume Migration during CO2 Injection in Deep Saline Aquifer
Authors B.O. Obioha and S.M. ShariatipourSummaryThe injection of carbon dioxide (CO2) in deep saline aquifer is a forefront strategic method to reduce emissions of CO2 in the atmosphere. CO2 is injected into deep saline aquifer as a supercritical fluid with density and viscosity that is less than the formation brine. This leads to CO2 upwards migration under buoyancy. Existing analytical solution did not account for permeability anisotropy (Kv/Kh) ratio. An analytical and numerical investigation was carried out into the effect of varying Kv/Kh ratios on the position of the CO2-brine interface. Existing analytical solution was then corrected to account for variation in Kv/Kh ratios. ECLIPSE 300 and Amarile’s RE-Studio were used for the pre and post processing modelling and analysis.
The result suggests that errors in the interface position (when Kv/Kh variation is not taken into account) is greater when viscosity dominates, but when gravity dominates, the errors are less significant. Numerical simulations agreed with the analytical model because the lowest Kv/Kh model resulted in more lateral extent due to viscosity effect, whereas higher Kv/Kh resulted in vertical migration due to gravity forces. Anisotropic permeability ratios are more important during injection. Analytical and numerical solutions suggest that variation in permeability anisotropy determines CO2 plume evolution.
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Experimental Investigation for the Effect of CO2 Sequestration on Oil Recovery under the Gravity Segregation in CO2 EOR
More LessSummaryThe integrating technology of EOR and CO2 sequestration would bring large quantities of CO2 storage capacity and increase recoverable oil, calling “Green Oil.” In CO2 injection process, the gravity segregation and miscibility condition are key factors to be successful for effective application of CO2 flooding. In this aspect, this study presents the results how can miscibility condition affect oil recovery and CO2 sequestration under the environment of gravity segregation. Most previous researches to improve CO2 EOR and CO2 sequestration have been conducted on one dimensional core flooding experiments which cannot reflect gravitational effect. This study performed the experiments on two dimensional sandstone plate being capable of gravity segregation phenomena. Our new experimental approach would be useful for designing the successful CO2 sequestration, particularly in thick reservoir dominating gravity segregation.
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Numerical Modeling for Assessing the Effects of Thermodynamic Properties on CO2 Storage in Saline Aquifers
Authors M. Pasdar, S.M. Seyyedi Nasooh Abad and B. RostamiSummaryAccording to the Intergovernmental Panel on Climate Change (IPCC), global CO2 emissions must be reduced by 50 to 80 percent by 2050 to avoid dramatic consequences of global warming. Geological storage of CO2 in saline aquifers is a promising method for reducing atmospheric CO2 concentration. For this aim, accurate modeling of CO2 sequestration into underground formations (saline aquifers) is required. In petroleum industry, normally this is achieved by using compositional reservoir simulators which is computationally expensive and time consuming. To overcome this, an accurate fluid model was coupled to a flow simulator to model CO2 sequestration in saline aquifers. Next, sensitivity analyses of thermodynamic properties (pressure, temperature and salinity) were done on some saline aquifers of Alberta basin, in Canada to investigate the effects of thermodynamics properties on CO2 dissolution in these aquifers. Results show that salinity has the strongest effect on CO2 dissolution in our studied aquifers compared to temperature and pressure effects. Results of this study enable us to assess the potential of each saline aquifer for CO2 storage and therefore help us in selecting suitable injection sites for CO2 sequestration.
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Creating a 3D Geologic Model for 2D Depth Migration in the Peruvian Andes
Authors R.W. Vestrum, J. Vilca, M. Di Giulio Colimberti and D.K. EllisonSummaryThe exploration block is located in the northern part of Ucayali Basin, in the backarc of the Andes mountains. The exploration target is in a compressive structure with high-angle faults caused by the reactivation of a normal fault. Typical to many foothills exploration settings, the block has comprehensive 2D coverage but not 3D surveys at the present time.
The exploration team chose anisotropic PSDM for the seismic data to correct for the pull-up below the structure. The data was low in data density and high in noise content, which made data-driven tomographic inversion unstable. The interpretive model-building process needs as many geologic and seismic constraints as possible to converge to an optimum velocity model.
Our desire to impose additional geologic constraints to the velocity model coupled with our concern about having a consistent velocity model across the block led us to build a 3D model from which we could extract a 2D model for each individual line. The method was highly effective for lines parallel to dip across the crest of the structure, but the models extracted from the 3D volume for lines oblique to the structure required further attention.
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Dip Constrained Tomography as Applied to Subsalt North Sea Data
Authors D. Carotti, C. Brillatz, P. Guillaume, A. Prescott and A. CavaliéSummaryDeveloped for the shallow channel anomalies in the North Sea, the dip constrained tomography can also be effective in subsalt areas, when geological dip constraints are known. Subsalt areas often suffer from noisy residual move-out information and limited angular coverage. In this work, we show that the introduction in the non-linear slope-tomography cost function of an additional term related to the offset-dependent imaged dips helps in stabilizing the inversion and the computed velocity perturbations. We use a North Sea example to demonstrate that the use of geological constraints in this extended tomography below complex overburdens improves the seismic image focusing and provides a more geologically plausible velocity model.
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Offset Dependent Picking and Image Guided Tomographic Modelling of Velocity Variations over the Hoop Fault Complex
Authors M.J. Hart, O.A. Adewumi, C. Lang and G. HilburnSummaryThe Hoop Fault Complex presents a significant imaging challenge, most notably where large velocity induced sags are evident in the footwall of the major areal extensional faults. These sags arise from large velocity contrasts across the fault. Resolving the velocity contrast is made more challenging by illumination issues resulting from the narrow single azimuth of acquisition. Previously, this velocity complexity had been addressed using both, fault and horizon-constrained tomography. Though largely successful, both of these approaches require subjective interpretation.
We present an objective data driven approach to resolve fault sags, which generated a more geologically realistic model of the Hoop Fault Complex than previously obtained via conventional tomography. Multiparameter offset-dependent picking was applied to model the complex moveout associated with this structure, in place of single parameter residual curvature picks. The tomographic update was then constrained by an image guided inversion. This resulted in a more geologically plausible velocity model, where layering and faulting are better honoured by the inversion update.
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Physical and Numerical Simulation of Conventional Induction Log Response of Fractured Reservoir
More LessSummaryThe feasibility of evaluating fractures in reservoir using conventional induction log has been analyzed by a physical simulation model and two kinds of numerical simulation models based on geometric factor theory in this paper. From simulation of 0.8m dual loop induction log and 1503 dual induction log which are widely used in oilfield, we conclude that fracture can be detected and evaluated from conventional induction log. The minimum fracture width conventional induction log can identify is 100μm, and the minimum interval between adjacent fracture 0.8m dual loop induction log and 1503 dual induction log can identify is 1.3m and 0.9m in preset model conditions.
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A New Implementation Means of Volumetric Method in Oil Reserves Calculation
More LessSummaryAs a common used method to estimate oil reserves, volumetric method hypothesizes that each calculated target is a homogeneous body and calculates the oil reserves based on several mean reserves parameters of the computing target. However, as is known, the reservoir heterogeneities exist widely in the earth. A new kind of volumetric method with high precision for oil reserves calculation has been proposed in this paper. This method divides the computing target into lots of small units and makes the small units have their own reserves parameters. QHD32-6 oil field has been taken as an example to show the workflow of this method, and the computing result has proved the accuracy of the method.
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The Application of Probabilistic Neural Network Analysis Technique in the Prediction of Sedimentary Tuff Reservoir
Authors F.L. Li, X. Guo, X.F. Zhang and J. ChenSummaryThe tigh oil reservoir in Tiaohu group in Santanghu Basin has the characteristics of high-density porosity, ultra-low permeability and high oil saturation, which are mainly controlled by the sweet spot of reservoir. And, the prediction of lithology and effective porosity is very important in the study of sweet spot of tight oil. Probabilistic neural network (PNN) is a kind of neural networks based on probabilistic thinking and Bayesian classification rules. when geological lithology or seismic attributes changes or modifies, the network can automatically adapt to the new variables, and adjust the weights until convergence; we use PNN analysis technique to establish a nonlinear statistical relationship between seismic attributes and logging curve, and finally use this relationship to identify lithology and predict porosity.
By applying of PNN analysis technique to predict lithology and porosity, we have confirmed that high porosity sedimentary tuff reservoir is mainly distributed in the north slope of the study area. In accordance with the results of reservoir prediction, all the proposed well sites have been drilled with high hydrocarbon flow from the Permian Tiaohu formation. The results show that the method is suitable for predicting sweet spot of the tight reservoir in the study area.
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A New Method for Porosity Estimation Based on Adaptive Critical-porosity Pride Model Using Seismic Data
More LessSummaryPorosity is a significant parameter for characterizing oil/gas reservoirs, and porosity estimation using seismic data is of great practical value. In the process, the accuracy of rock physics model and the inverted density are the two most important aspects. This paper proposes a new rock physics model (adaptive critical-porosity Pride model), which can be used to calculate dry rock bulk modulus with more precision. The new model dynamically adjusts solidification factor, and critical porosity, which means it fully takes the influence of pore shapes into consideration. Then, based on Gassmann equation, combined with the new rock physics model and density data from pre-stack noise-resistant density inversion, a new nonlinear chaotic quantum particle swarm optimization algorithm is used to obtain porosity, which can greatly enhance the uniqueness of solutions. Lastly, the seismic inversion porosity method is applied to ZG8 area in Tarim Basin in China. The results show that the inverted porosity from seismic data is in good agreement with the logging data, which proves that this method can be feasible and applicable in carbonate reservoirs.
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How to Infer Porosity from Seismic Data by Using Effective Medium Modeling? A Case Study in the Fort Worth Basin
Authors M. Adelinet and M. Le RavalecSummaryMany geophysical studies in reservoir characterization focus on the variations in the elastic properties of rocks. They commonly involve seismic data, which are processed in terms of seismic attributes. These processed data still have to be related to the physical properties of the rock mass and the fluids saturating the pore space. This need motivated the development of research projects referring to the effective medium theory (EMT). In the present, we refer to EMT to infer porosity data from seismic impedances within a fractured reservoir. The leading idea is to take advantage of the available impedances to characterize the spherical porosity and the crack density. We develop an effective medium model that provides numerical responses for seismic impedances. These responses are then compared to the impedances obtained from stratigraphic inversion. The overall procedure consists in adjusting the input parameters of the EMT model, which are spherical porosity and crack density, to minimize the impedance mismatch. Our case study concerns the limestone formations of the Fort Worth Basin (Marble Falls and Ellenburger formation). Results are promising and the EMT could be a very useful tool to explain reservoir and geophysical data in terms of microstructural properties, in particular for fractured reservoirs.
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Two-parameters Approximation and Stable Elastic Impedance Inversion for λρ
More LessSummaryLamé petrophysical parameters is λρ the central parameter for lithology discrimination in oil exploration. We often obtain it by indirectly calculating of compressibility, shear and density information via three parameters inversion. The density term always can’t be inverted stably, it will provide the λρ volume. And three parameters inversion methods are often plagued by numerical instability. In order to avoid estimating the density and enhance the stability of inversion, we reduce the dimension of model space by simplifying the three parameters Gray approximation based on λ, μ and ρ to the two parameter approximation based on λρand μρ. Tests on synthetic data and real data application show that our λρ extraction method by two term elastic impedance inversion is effective for lithology discrimination.
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Seismic Data Preconditioning for Fault Imaging Using Polynomial Fitting
More LessSummaryWe propose a new 2-D structure-enhancing polynomial fitting filter to suppress random noise and preserve edges in seismic data prior to the computation of seismic attributes, such as coherence. Our 2-D filter is an extension and enhancement of the 1-D polynomial fitting filter that has proven effective in suppressing noise and preserving edges in 1-D data but is not as effective on 2-D data. Experimental results show our 2-D filter preserves and enhances structures while suppressing noise in 2-D data more effectively than a 1-D polynomial filter.
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Integrated Rock Physics based Seismic Inversion Workflow for Reservoir Characterization - Carbonate Case History
Authors B. O’Connell, F. Ruiz and F. ObregonSummaryCarbonate reservoirs are not known for having a large AVO signature. Because of this, a uniquely integrated workflow was created.
In this paper we outline how we characterised a geologically complex set of carbonate reservoirs reservoirs identified with seismic of limited bandwidth, by using Rock Physics, seismic preconditioning and geological velocity analysis.
The resulting inverted P-Impedance and VpVs ratio volumes alow for confident porosity volume creation and prediction of lithology.
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