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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
961 - 980 of 1034 results
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Automatic Joint Location and Velocity Inversion for Passive Seismic Data
Authors B. Schwarz, A. Bauer and D. GajewskiSummaryIn this paper we present a new automatic and fully data-driven approach for the location of passive seismic events with simultaneous velocity model building. The suggested scheme is a two-step process, in which first, coherence-based moveout analysis is used to efficiently extract local emerging wavefront properties, including the propagation times, from each recorded event. Following the attribute extraction, we employ highly convergent wavefront tomography, which can also be utilized for active seismic applications. Wavefront tomography is strongly guided by the estimated coherence and, therefore, can be fully driven by the transformed data. Due to the fact, that the moveout analysis incorporates the locally phase-consistent summation of amplitudes, the proposed scheme has the additional benefit that the signal-to-noise ratio, which can be very low in passive seismic applications, is naturally enhanced and data gaps can be filled. Concluding this work, we prove the applicability of the method with a synthetic data example, where three passive events were successfully located in a vertically and laterally heterogeneous velocity model. Only based on the very low number of three recorded events, wavefront tomography was, in addition, able to jointly recover the overburden velocity structure, without the need of any user-interaction and a priori information.
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Micro-seismic Imaging Using Source-independent Waveform Inversion
Authors H. Wang and T. AlkhalifahSummaryUsing full waveform inversion (FWI) to locate microseismic and image microseismic events allows for an automatic process (free of picking) that utilizes the
full wavefield. However, waveform inversion of microseismic events faces incredible nonlinearity due to the unknown source location and function (time).
We develop a source independent FWI of microseismic events to invert for the source image and the velocity model. It is based on convolving reference traces with the observed and modeled data to mitigate the effect of an unknown source time. The adjoint-state method is used to derive the gradient for the source image and velocity updates. By inverting for both the sources image and the velocity model, the proposed method produces good estimates of the source location and the background velocity for part of the Marmousi model.
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Automated Event Localisation Using the AIC Characteristic Function - Application to Microseismicity Around Sumatran Fault
Authors A. Hendriyana, K. Bauer, U. Muksin and R. SuleSummaryAutomated event localisation results could be improved by transforming amplitudes of waveform to characteristic functions such as trace envelope, STA/LTA, kurtosis and power density function. The goal of this study is to evaluate the performance of Akaike Information Criterion (AIC) function in providing accurate seismic event locations when it is used as the characteristic function. We tested the method to passive seismic data acquired in a local earthquake study around the Sumatran fault, Indonesia. By picking the maximum semblance as event location, our results show that the seismic events delineate Sumatran fault well. We also compared the located seismic events with those computed using the well known STA/ LTA characteristic function. By using double-difference results as reference, we found that the located seismic events associated with AIC showing better focusing than STA/LTA results.
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Ambient Noise Tomography in the Adana Basin of Southern Turkey
Authors T. Bakirci, A. Kaslilar and A. KocaogluSummaryWe investigate the seismic velocity structure of the Adana Basin located in Southern Turkey by using the method of ambient noise tomography. The vertical-component continuous data were recorded by 21 broadband stations located in and around the basin. The Green’s functions are obtained from three-year stacks of cross correlations between each pair of stations. The Rayleigh group velocities are measured for the period range 8 to 22 s. Tomographic images (localized group velocities) show that the lateral variation of velocity structure can be observed and are correlated with the geology.
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Real-time Earthquake Search Engine with Historic Data for Database
More LessSummaryTo monitor and report earthquake parameters that include location and source focal mechanism in real time in a local or regional scale, we apply a search engine approach to find the best waveform matches to any new event from a pre-established database. In such a small scale area for monitoring earthquakes, earth heterogeneity strongly influences high-frequency seismic wave propagation. Conventional 1-D theoretical seismogram calculation is likely inaccurate enough to match data. Fortunately, in Jinggu, Yunnan, China where we are monitoring earthquake activities, there were over ten thousands of small earthquakes (Ms>1.0) in 2014 in an area covering 100 km by 100 km and from 5 to 20 km in depth. Since these events occurred near an existing fault and the coverage is sufficient, we use these events to create a historic database. When any new earthquake occurs in the same area, we apply a fast search engine approach to find the best match among historic data and estimate its location and focal mechanism immediately using the search results. For any event outside the database coverage area, the search engine can easily differentiate that using a similarity criterion.
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Anisotropic Source Mechanism Construction and Waveform Modelling
Authors N. Boitz, A. Reshetnikov and S.A. ShapiroSummaryIn this study we determine the effect of anisotropy on source mechanisms and wave propagation in a VTI-medium.
We show, that the effect of anisotropy has a significant impact on the polarity and amplitude of P-wave for normal and thrust fault and cannot be neglected.
Using this information we calculated synthetic seismograms which should explain our data better compared to pure isotropic synthetic seismogram modeling
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Seismic Imaging of Salt-influenced Compressional Folds
Authors D.C. Castillo Valencia, C. Botter, S. Hardy and N. CardozoSummaryFold-and-thrust belts (FTB) detaching on salt can develop hydrocarbon structural traps. However, seismic data do not allow a reliable understanding of the FTB internal structures and properties. A methodology is proposed to assess the impact of FTB deformation on seismic. The FTB is mechanically modeled using a discrete element method (DEM), finite strain in the DEM is used to update the base seismic properties of the model, and a ray-based prestack depth migration (PSDM) algorithm is used to produce a seismic image of the structure. This workflow is illustrated in a 2D DEM model, which consists of a brittle (siliciclastic)-ductile (salt) sequence under imposed shortening, which initiates and propagates thrust faulting through the siliciclastic sequence. Seismic images are simulated for the brittle cover (interlayered sequence of sandstone and shale) for two different wave frequencies of 10Hz and 30Hz. At higher frequency (30Hz) the complexity of the larger thrust faults can be better represented than at the lower 10Hz frequency image. Acquisition and processing parameters can be evaluated for better seismic imaging of salt-influenced compressional folds.
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Using Effective Medium Theory to Better Constrain Full Waveform Inversion
Authors M. Afanasiev, C. Boehm, D. May and A. FichtnerSummaryWe formulate seismic inversion as a constrained optimization problem, with constraints derived from effective medium theory.
The work stems from the intuitive observation that, when applying high-resolution imaging techniques such as full waveform inversion, the long-wavenumber components of the model converge first. By using effective medium theory, we define a feasible set of allowable fine-scale model updates, with the constraint that the converged long-wavenumber model components must not change. If a proposed update lies outside this feasible set we use a projection method to ensure feasibility. Once feasibility is ensured, we solve an inexpensive auxiliary optimization problem which returns a model closest to the proposed update, while still lying within the feasible set.
As a proof of concept we test our method in layered media. This allows us to analytically define our effective medium equations, using the Backus parameters. The tests show that the projection and auxiliary optimization successfully removes artefacts from challenging and noisy model updates, while retaining those portions of the updates carrying relevant information.
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Testing and Comparing Stacks of Different Seismic Attributes for Micro-Seismic Event Detection
Authors F. Motz, J. Kummerow and S.A. ShapiroSummaryThis work is divided into two stages. At first we are using P-picks from 16 events and 1551 receivers to create a master event set. We interpolated the move-out curves of each receiver line using different fitting methods and combined them into one master move-out curve set.
In the second part we stack seismic parameters according to the master move-out curves to maximize the signal-to-noise ratio in order to locate new events within the rest of the data set. The earlier created master event set will be used to minimize the parameter search effort. They will narrow down the search for the optimal move-out curve. Iteratively stacking over the interpolated move-out curves will then result in detecting new events within the data set.
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Passive Source Illumination Compensation Based Full Waveform Inversion
Authors P. Zhang, L.G. Han, Z.Y. Jin and F.J. ZhangSummaryThe high velocity structures always produce shielding effect to the low velocity structures below them in conventional full waveform inversion (FWI), which leads to few reflected information recorded on surface corresponding to those low velocity structures. The insufficient illumination will influence the final results of FWI, especially on deep structures. Here we consider compensating the insufficient illumination of active seismic sources using passive seismic sources. Based on conventional FWI, we introduce the constraint with passive seismic data, and propose a strategy for passive source illumination compensation based FWI. Firstly, we discuss the relationship between the accuracy of velocity model and the estimation of source locations and wavelets. Then we provide the workflow of this strategy. Numerical example shows this illumination compensation strategy can provide more detailed deep information.
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Seismic Wavelet Estimation through Phase Retrieval
Authors S. Vafaei Shoushtari and A. GholamiSummaryA reflection seismogram, after some specified processing steps, can be regarded as a convolution of the source wavelet with the reflectivity series and added noise. A wavelet is defined by its amplitude and phase spectrum. Determining an appropriate phase in the time domain has always been a problem. In this paper, wavelet estimation through phase retrieval is proposed in two sequential steps. In the first, the reflectivity model is obtained only by the amplitude spectrum of the observed data. In the second, the seismic source wavelet is estimated using the obtained reflectivity. We deal with an ill-posed inverse problem which has to be solved through regularization. The proposed phase retrieval algorithm has no limitations for the phase of the estimated wavelet. The mentioned procedure is examined on both synthetic and real seismic sections to obtain reflectivity model and the source wavelet. Eventually the good performance of the proposed algorithm is demonstrated.
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The Frequency-dividing Multiple Matching and Subtraction Technology Based on Shearlet Transform
More LessSummaryIt is necessary to have multiple matching during multiple elimination, because there were wide differences between predicted multiples and original records on amplitude and phase caused by the convolution of trace gathers. Conventional multiple matching always use the least-squares matching while the amplitude matching may cause border effect and waveform distortion, and the least-squares subtraction often leads to unsmooth adjacent sample points.Shearlet is a new multi-scale transform with multi-directions, local property, and optimal sparse approximation properties which can be used for presenting multidimensional data.In order to adapt the above-described matching error and obtain more continuous primary event, we combined shearlet transform with multiples matching an use shearlet thereshold subtraction instead of conventional least-squares subtraction. The result shows that this method has better effect.
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Implementation of Improved Reverse-time Migration via Acoustic Impedance Equalization
More LessSummaryWhen performing migration, reflection energy from discontinuities of velocity field may result in poor images. To suppress reflection energy, therefore, a smoothing filter is usually applied to the velocity model. But the velocity smoothing spoils the geologic plausibility of the velocity model. In this paper, we attempt to minimize migration artifacts by equalizing acoustic impedances over the entire model. To equalize acoustic impedances, we introduce fake density concept which compensate the velocity difference. If acoustic impedances are constant at every layer, reflection coefficients become zero at normal incidence and reflection energy is minimized at non-normal incidence. Then the migration result can be improved. To verify fake density concept, we implement a reverse time migration using cell-based finite-difference method. Through the numerical examples for the SEG/EAGE salt model, we show that the reverse-time migration using fake density improves the quality of migration image.
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Annular Flow Modelling in in Advanced Well Completion
Authors M. Moradidowlatabad, M. Abdollahi, H. Vafaei and F. RashidiSummaryThe (A)ICD completion has proved to be an effective solution to mitigate water and gas breakthrough and coning problems. One of the major parameters affecting the (A)ICD completion’s performance is annular flow, the flow of the fluid in the space between the base pipe and the sand-face [1,5]. It is widely accepted, and proven by modelling, that the ICD completions can minimise the annular flow in perfectly horizontal wellbores in perfectly homogeneous reservoirs as no AFI was used in the first ICDs completion in Norway in 1997. The importance of annular flow on the (A)ICD completion was addressed by many researchers. However, there was lack of an analytical annular flow model to integrate the effect of all parameters important contributing to the annular flow.
In This paper, The first analytical formula to address the annular flow for an ICD completion is derived. It is illustrated why a sufficient strength (A)ICD design could reduce the need for AFIs by minimising annular flow in homogeneous reservoirs. The equation also helps obtaining an appropriate strength of (A) ICD completion in such reservoirs.
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The Influence of Discontinuities in the Reservoir on Well Productivity
More LessSummaryThis paper discusses the modelling of the fluid flow process to the well in the presence of fractures (inclusions) with different permeability. The fracture may be either natural, in case of tectonic fault, or artificial, in case of well simulation, and it may have various permeability values. Therefore, oil filtration modelling in fractured reservoirs is also interesting from the point of view of application for hydraulic fracturing. Skin effect is one of the most important parameter for evaluation the productivity of the well, therefore the expression for skin is defined in the paper for different locations of the well and the fracture and for different values of fracture conductivity.
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Optimization of Multilateral Well Productivity in Carbonate Reservoirs
More LessSummaryThe merits of the application of multilateral wells are well documented in the literature however, an understanding of the best operating conditions for the use of multilateral wells is rare thus we answer cogent questions related to the optimization of multilateral wells under different reservoir conditions and well design parameters.
To answer such questions, Design of Experiment (DOE) and Response Surface Methodology (RSM) was utilized. Selected factors to be optimized are the number of laterals, length of horizontal sections, correlation lengths for heterogeneity indication, reservoir thickness, and permeability anisotropy. These factors were chosen based on literature search, perceptions and deliberations while the objective functions are the cumulative oil production and water cut. Several experiments were conducted using extensive three dimensional fine scale numerical simulations and the Box-Behnken response surface methodology was used to derive the response surfaces. Single effects and interaction plots are made to show the interactions between parameters and the effect of these parameters and interactions on the objective function. This study provides a template for decision making in field development operations thereby reducing uncertainties and maximizing gains.
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Carbonate Acidizing Optimazation in Iranian Oil Field
Authors H. Asaadian and B.S. SoulganiSummaryThe main point in matrix acidizing treatment optimization is to reduce the skin factor in every single stage of injection and finally reaching the minimum value. If the skin effect owning to damage is quantified, then the treatment must reduce the total skin effect by that amount. Further, to be cost-effective, the injected volume and the pumping time should be minimized. The goal of this study is to evaluate various acidizing treatments for three wells placed in south east of Iran.
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Attribute Analysis of Fractured Reservoir - A Case Study from the Carpathian Basement
By M. DrwilaSummaryIn this study seismic attributes were used to verify if fracture density, their orientation and distribution can be connected with good reservoir parameters and gas saturation. The reservoir is located in Upper Jurassic carbonates which create the top of the Paleo-Mesozoic basement of northern Carpathians.
Results showed that areas with higher fracture density pin-pointed by attributes correspond to reservoir zone discovered by 3 wells. Fracture orientation derived from dip deviation attributes is rather chaotic. On the location of the well D dip deviation indicated fracture orientation in direction N-S what is parallel to compression direction in the region. Nonetheless well is negative and was drilled in the area of low fracture density and high reflection amplitude.
Conducted analysis helped to point out new areas with possible permeable fracture network.
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Frequency-dependent Velocity Analysis and Offset-dependent Low-frequency Anomalies from Hydrocarbon-filled Reservoir
Authors S.S. Ahmad, R.J. Brown and A. EscalonaSummaryUsing various spectral decomposition techniques, low-frequency amplitude anomalies at and below hydrocarbon-filled reservoirs were investigated. For this purpose, a 3D seismic dataset situated in the southern North Sea adjacent to the Denmark and United Kingdom sectors was used. Geologically the area lies in the depression between the NW-SE-trending Lindesnes ridge in the NE and the NW-SE-trending Grensen nose in the SW. The observed low-frequency amplitude anomalies were found to be offset-dependent, being strong on the near-offset traces but absent on the far-offset traces. Additionally, horizon velocity analysis was performed along the tops of reservoir and non-reservoir intervals to look for any possible change in velocity with frequency, or other evidence of dispersion. The NMO velocities calculated from the top of non-reservoir events were found to be the same for both the low- and high-frequency filtered CMP gathers. However, where we observed low-frequency amplitude anomalies at and below oil-filled reservoirs, we also observed low velocity for low-frequency and high velocity for high-frequency filtered gathers. Moreover, this change in velocity was not seen in the low-frequency anomalies observed from gas-filled reservoirs
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Analysis of the Geothermal Anomaly from the Romanian Part of the Pannonian Basin
By A.I. MicuSummarySeveral geothermal structures were identified in the Romanian territory after the integrated analysis of the geophysical data, represented by geothermal, seismic, gravimetry and hydro-geological data. The most important geothermal structures were found in points inside the eastern segment of the Pannonian Basin, such as the Timis area, and in the Moesian Platform. The analysis of seismic data, made available by industry in this area, shows that the higher heat flows are present in areas in which basement blocks rise closer to the surface. Deep faults and system of faults are visible on the seismic sections. The processing of the seismic reflection data was done using a flow based on that one used in industry.
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