- Home
- Conferences
- Conference Proceedings
- Conferences
80th EAGE Conference and Exhibition 2018
- Conference date: June 11-14, 2018
- Location: Copenhagen, Denmark
- Published: 11 June 2018
21 - 40 of 1073 results
-
-
Image Domain Least-Squares Migration with Hessian Estimated by Non-Stationary Matching Filters
More LessSummaryThe key to image domain least-squares migration is the explicit calculation of the Hessian matrix. However, the full Hessian matrix is too big and expensive to compute and save. Guitton (2004) directly approximates the non-diagonal inverse of the Hessian with a bank of non-stationary matching filters, which can be seen as a low-rank approximation of the true inverse Hessian. The filters have the amplitude-balancing effect, but the ability to increase the resolution is missing. In this paper, to capture as much effect of least-squares migration as possible, we use non-stationary matching filters to approximate the non-diagonal Hessian first, and then solve a constrained optimization problem with the sparse and TV regularization for the result of the image domain least-squares migration. Numerical examples illustrate that the inverted images of the proposed method have both more balanced amplitudes and higher resolution than conventional migration images.
-
-
-
Double Plane Wave Least Squares Reverse Time Migration with Sparse Frequency and Pane Wave Sampling
More LessSummaryLeast squares reverse time migration (LSRTM) is often formulated as an iterative updating process, where estimating the gradient of the misfit function is necessary. Traditional time domain shot profile LSRTM is computationally expensive because computing the gradient involves solving the two-way wave equation several times in every iteration. To reduce the computational effort of LSRTM, we propose to implement frequency domain LSRTM using double plane wave (DPW) data with sparse frequency sampling and sparse plane wave sampling. Theoretically, frequency sampling and plane wave sampling used in migration should obey the Nyqusit theorem. Otherwise, the well-known wrap-around artifacts and linear artifacts might contaminate images. In this research, we demonstrate that images with correct reflector amplitudes and reasonable resolution can be achieved even if frequency sampling and plane wave sampling are larger than that determined by the Nyquist theorem. The artifacts generated due to undersampling in frequency and plane wave can be effectively suppressed during iterations. Using sparse frequency and plane wave sampling for DPW LSRTM greatly reduces the number of wavefield computations. We show that the computational efficiency can be improved by an order of magnitude.
-
-
-
Wavefield Transmission Imaging with Reverse Time Migration
Authors C. Willacy and M. KryvohuzSummarySteep salt boundaries can be poorly illuminated or completely absent in the migrated image. To provide a solution to this problem, we apply two reverse time migration imaging methods which use transmitted (refracted) wavefields. In the first technique, down-going waves, typically recorded in walkaway VSP surveys, are used to image the salt flank via the generation of aplanatic isochrones. It is demonstrated that this image can be generated in the absence of an explicit interpretation of the salt flank. In the second technique, we extend the basic theory to include imaging of up-going source wave fields which then refract at the base salt, as acquired by a surface acquisition geometry. This technique has similarities to the prism-imaging method, yet it uses transmitted instead of reflected waves at the salt boundary. We demonstrate that this is not only a viable technique for imaging of the salt boundary, but also to determine the correct salt velocity when used in conjunction with conventional reflection imaging. A combination of synthetic and field datasets is used to demonstrate the transmission imaging methodologies for imaging salt flanks with reverse time migration.
-
-
-
A Separated Formulation of the Elastic Wave Equation in P- and S-potential Fields
More LessSummaryElastic wave imaging has been a significant challenge in the exploration industry due to the complexities in wave physics and in numerical implementation. In this paper, we derive the elastic wave equations without the assumptions of homogeneous Lamé parameters to capture the mode conversion between the P- and S-waves in an isotropic, constant-density medium. The resulting set of two coupled second-order equations for P- and S-potentials clearly demonstrates that mode conversion only occurs at the discontinuities of the shear modulus. Applying Born approximation to the new equations, we derive PP and PS imaging conditions as the first gradients of waveform matching objective functions. The resulting images are consistent with the physical perturbations of the elastic parameters, and hence are automatically free of the polarity reversal artifacts in the converted images. When implementing elastic reverse time migration (RTM), we show that scalar wave equations can be used to back propagate the recorded P-potential, as well as individual components in the vector field of the S-potential.
-
-
-
A Wavefield-separation-based Elastic Least Squares Reverse Time Migration
More LessSummaryCompared with the elastic reverse time migration (ERTM), ELSRTM can produce images with higher spatial resolution, more balanced amplitudes and fewer artifacts. However, the crosstalk between compressional (P-) and shear (S-) waves can significantly degrade the imaging quality of ELSRTM. We developed an ELSRTM method to suppress the crosstalk artifacts. This method includes three crucial points. The first is that both the forward and backward wavefield are extrapolated based on the separated elastic velocity-stress equation of P- and S-waves. The second is that the separated vector P- and S-wave residuals are migrated to form reflectivity images of Lamé constants λ and μ independently. The third is that the reflectivity images of λ and μ are obtained by the vector P-wave wavefields achieved in the backward extrapolation of the separated vector P-wave residuals and the vector S-wave wavefields achieved in the backward extrapolation of the separated vector S-wave residuals respectively. Numerical tests with synthetic data demonstrate that our ELSRTM method can produce images free of the crosstalk artifacts.
-
-
-
Channelized System Reservoir Characterization Using Diffraction Imaging - Practical Aspect of a Novel Technique
Authors J. Soldo, M. Koremblit, D. Lorenzo and M. SuarezSummaryThe seismic processing technique known as “Diffraction Imaging” has demonstrated to be an interesting method in order to map geological sub surface discontinuities, in special those high frequency features related to such as discontinuities. They have been study in the prestack time as well as in the prestack depth domain by several authors. Detection of geobodies (channel system) is important when developing continental type sandstone reservoirs. Understanding the location and orientation of such as features is important for optimal well placement and field delineation. Seismic diffraction can be used for imaging not only systems of natural fractures but also for mapping wedge limits caused by channels. Diffracted waves are created when an incident wavefield encounters small size objects or even discontinuities such as faults, sharp curvature geoforms or wedges. The diffractive portion of this wavefield can be extracted from its total in order to produce images that contain information regarding subsurface scattered energy due to discontinuities. This is the first time that this technique is applied in the company in order to characterise and improve the delineation of channel systems.
-
-
-
A Holistic Approach to Model-Building in and around Injectites: A Case-Study Offshore Norway
Authors V. Valler, N. Payne, T. Hallett, M. Kobylarski, G. Venkatraman, J. Rappke and D. FaircloughSummaryThe presence of injectites is a common and often time consuming area to be addressed during velocity model building. In addition to their impact on deeper structures and prospects, re-worked injectites are increasingly being considered for hydrocarbon potential themselves. In order to handle the challenges above we should consider ways of producing an accurate velocity model of these structures within a framework that is efficient and commercially time-viable. Here we present a holistic approach and case study to model-building in and around injectites that utilizes robust broadband data pre-processing, a semi-automated identification and modeling of injectite bodies and subsequent high-resolution tomographic updating. Our results show that this method enables us to produce a highly accurate and detailed model of a complex injectite field and subsequent improvement on the deeper image within the timeframe of a conventional model building iteration.
-
-
-
Separated Wavefield Imaging for Ocean Bottom Surveys - Feasibility Study of Receiver Decimation on a North Sea Dataset
Authors D. van der Burg, T. Martin, A. Asnaashari, S. Perrier, J. Fasterling and J. MusserSummaryWe present a method for imaging with separated wavefields from an ocean bottom cable acquisition to deliver images of the subsurface with enhanced illumination and angular diversity. Using this data, we investigate whether it is feasible to decimate the sources or receivers without degrading the structural image from separated wavefield imaging. We conclude by determining if this would be beneficial to reduce acquisition cost and to provide illumination below obstructions like a platform hole.
-
-
-
Reservoir Imaging Using Fwi, Q-Tomography & Bayesian Classification - Black Sea Case Study from Acquisition to Drill Bit
Authors O. Costriiciuc, A. Fogg, R. Holden and J. MooreSummaryBlack Sea Oil and Gas’ concession XVa Midia is on the Romanian continental shelf of the Black Sea which the company operates on behalf of its partners Gas Plus International BV and Petro Ventures Resources SRL. This study demonstrates how a suite of seismic processing and QI (Quantitative Interpretation) technologies was optimised to fully resolve gas assets currently under development and highlight satellite exploration targets in Miocene to Pliocene age (late Pontian to Dacian) fluvio-deltaic sands and claystones. Near surface channel features and localised gas presence causes seismic imaging issues as amplitudes are attenuated and time structural push-downs are observed. A 3D survey was acquired during 2016 and processed together with three legacy 3D surveys. This data was used for exploration well planning for a drilling programme of two wells Q4 2017. During the seismic processing tests were run to investigate possible imaging improvements using Full Waveform Inversion (FWI) and Q-tomography. A subset of the 3D was reprocessed using these methods during Q4 2017. This presentation will demonstrate the imaging uplift achieved and the impact on the interpretation together with pre and post drill results guided by QI based on pre-stack seismic inversion and facies/fluid probability classification.
-
-
-
Reviving a Mature Basin through High-End Imaging Technology
More LessSummaryThis paper highlights compelling imaging improvements achieved through modern high-end reprocessing in the Gippsland Basin. The area of study, largely represented by the Bass Canyon, has strong exploration potential as well as high risks. The major challenges in this region are related to geologic complexity and seismic imaging limitations, i.e.: a) extensive velocity anomalies leading to velocity uncertainties and false structural closures that increase drilling risk; b) strong noise interference and limited imaging clarity that affects AVO analysis. By integrating the modern techniques of 3D deghosting, full waveform inversion (FWI) and least-square Q pre-stack depth migration (LSQPSDM), the newly reprocessed data yields a substantial amount of added value over legacy datasets, resulting in an improved understanding of the subsurface geology and clearer prospect mapping. This reprocessing approach demonstrates, even in basins that are considered mature, that new ideas and technology can change long-held perceptions and rejuvenate exploration interest.
-
-
-
Salt-Related Converted-Wave Attenuation – a Deep-Water Example
Authors M. Hegazy, A. Stewart, S. Hydal, K. Malave, O. Zdraveva and O. MataraciogluSummaryComplex shallow salt canopies, such as those found in offshore basins in the Gulf of Mexico, Brazil, and West Africa often suffer poor illumination, which results in poor subsalt imaging. The geometry of subsalt horizons truncating against the base of salt often determines if a trap exists and if it will be economically viable. It is, therefore, important to get an accurate image in these areas to reduce the seismic uncertainty. Unfortunately, the presence of converted mode energy can add spurious complexity to the subsalt image and degrade subsalt target interpretation. A novel C-wave attenuation workflow is introduced to address the C-wave energy. Synthetic and field data examples show a significant improvement in the image interpretability and demonstrates the importance of this application to earth model building and amplitude variation with offset AVO work
-
-
-
Ultra-Large-Scale Wide-Azimuth Acquisition and Broadband Imaging in the Campeche Basin
Authors S.L. Yong, O. Zdraveva, E. Medina, S. Savoie and K. LyonsSummaryThe recent opening of Mexican acreage to foreign companies created a need for reliable regional interpretation over large prospective areas and lead to the wide-azimuth acquisition of new seismic data over ∼70,000 km2 in the Campeche basin. In this work, we discuss the overall acquisition and imaging strategy, allowing us to create high-quality, contiguous, broad-band images over large area of extreme geologic complexity in a short turnaround time. We describe all aspects of this strategy from the staged acquisition and fast-track products delivery, through broad-band processing and high-resolution anisotropic earth model building, to the use of complementary migration algorithms enabling supra-salt and subsalt target evaluation in this vast and prospective area located in the most southern part of the Gulf of Mexico.
-
-
-
Unfolding Marine Multiazimuth Data from the Gulf of Mexico
Authors H. Roende, G. Hilburn and D. BateSummaryThe first evolution of WAZ seismic data acquired over 10 years ago provided a sizable uplift over previous NAZ data sets. The addition of orthogonal surveys, advances in data processing, and improved geological understanding have recently introduced another step change in the data quality. These improvements are now leading to a greater improvement in data analysis and interpretation than just structural imaging uplift. We can see 4 distinct behaviors in 6 azimuth M-WAZ marine data. When data is acquired over “simple” geology, we get common signal in all azimuths. We also notice that close to salt, there are major differences between the 6 azimuths over large depth ranges due to illumination. These two observations have been known and published for the last decade. Our findings show that there are untapped potential and knowledge in marine M-WAZ data if acquired and proccessed correctly. We believe that we can map azimuthal-amplitude variations, and therefore, map stress and fracture fields to facilitate the production of hydrocarbons. If the data is acquired with a significant time lapse between acquisition, there is also an opportunitiy to perform 4D studies.
-
-
-
Seismic Re-processing and Q-FWI Model Building to Optimise AVO and Resolution in the Shallow Wisting Discovery
Authors G. Apeland, P. Smith, O. Lewis, S. Way, H. Veire, N. Stevens, L.M. Moskvil and J.R. GranliSummaryThe Wisting discovery in the south-west Barents Sea is a laboratory for geophysical studies due to its shallow reservoir and complex geological history. This discovery is constantly highlighting aspects of conventional seismic processing that require new approaches and technologies to allow AVO to be preserved and understood. Previous studies at the Wisting discovery have highlighted the importance of imaging in the depth domain with an accurate earth model for AVO preservation, including accounting for absorption within the imaging itself. In addition, AVO studies over the discovery have highlighted shortcomings with conventionally acquired and processed seismic datasets; The lack of near angles has made AVO studies over the discovery challenging and the AVO extracted from the seismic has not matched the modelled AVO at well locations. Following on from the recommendations of the previous AVO studies, OMV and partners initiated a reprocessing project that would focus on combining all previous experience with the Wisting seismic data. This paper describes the FWI model building and time reprocessing performed, and how we tailored the processing and QC to optimize the AVO response in the shallow section.
-
-
-
Wave-Equation-Based AVO Inversion in the Presence of Coal Seams. A Synthetic Study from the Cooper Basin, Australia
Authors D. Gisolf, P. Haffinger, P. Doulgeris and S. SquireSummaryCoal seams, being very soft and light, cause strong internal multiple reflections and mode-conversions, as well as strong transmission effects. Conventional AVO inversion based on primary reflection coefficients only, will not be able to distiguish the primary from the multiple energy and consequently produce spurious results. Wave-Equation-Based AVO inversion, being based on the full elastic wave-equation, is able to account for all these effects and image the coal seams properly. Like all other AVO techniques, the WEB AVO is applied in the 1.5D data domain. In this paper we consider the logs from the well Moonanga-1 in the Cooper Basin in South Australia. This area is notorious for the presence of coal seams, hampering seismic interpretation. Full elastic synthetics are produced from the logs. The results from conventional Sparse-Spike-Inversion and from WEB inversion of the synthetic gather are compared, showing a clear improvement for the WEB inversion. This will lead to much better interpretability of the inverted data.
-
-
-
Quantifying the Effect of Overburden Multiples on Miocene Reservoirs in the Levantine Basin
Authors P. Doulgeris, D. Anestoudis, P. Haffinger, A. Droujinina and D. GisolfSummaryThe Karish Main field was discovered in 2013 in the Levantive Basin, 75km offshore the northern coast of Israel. The Oligocene-Miocene submarine fan systems form the primary reservoirs of most commercial hydrocarbon discoveries to date in the region. At the end of the Miocene, the Mediterranean Sea became isolated from the Atlantic Ocean, which led to the deposition of up to 1,500 m of evaporites. The prospect was supported by seismic amplitudes and was proven by drilling well Karish-1. The aim of the current study is to model and understand the impact of the overburden evaporite on the seismic response of the reservoir. The wave-equation-based interbed multiples investigation technique deployed was able to identify the major multiple generators while quantifying the level of constructive interference expected on amplitudes at reservoir level from overburden multiples.
-
-
-
AVAZ Quantitative Interpretation Based on Orthorhombic Medium-Part Two: AVAZ Inversion
More LessSummaryIn this paper, we mainly talk about orthotropic AVAZ inversion technique, it has proven to be important and effective for shale gas evaluation and development. We use pre-stack AVAZ inversion to predict elastic properties, it is carried on pre-stack azimuthal gathers with constrained wells. A slight modification was made on the basis of Bachrach’s (2004) equation in order to obtain elastic parameters such as P-wave impedance, S-wave impedance, combinations of anisotropic parameters and fracture orientation from inversion. This work could offer multiple elastic parameters that characterize the quality of shale reservoirs. This method is successfully applied in real data of Sichuan Basin, it shows that the results of inversion are effective and reasonable.
-
-
-
Regional Porosity Estimation in Danish North Sea Chalk
Authors H. Wagner, H. Klemm and P. GeltingSummaryWhen performing seismic inversion over a large area we often face lateral changes in the seismic signature not related to the geology of the target. Therefore a methodology to equalize seismic data over large areas was developed. The methodology was used to prepare the data for absolute seismic acoustic inversion. The P-wave impedance result was subsequently transformed into porosity via a relationship from well data. The methodology builds on the ability to assess differences in data using an un-biased wavelet and well tie estimation method. The method is utilized to correct for data issues without removing geologic information. We did this by constructing a matching filter from a wavelet parametrization that varied with depth. The methodology was successfully applied for regional porosity estimation over an area of 6400 km2, or more than 40 million seismic traces, in the Danish North Sea. The regional nature of the results is beneficial for the large scale geological understanding of the area especially for exploration purposes. Furthermore, it provides insights into relations between porosity and geomorphology, and helps identifying new exploration opportunities.
-
-
-
Seismic Inversion for Statfjord Well Maturation
Authors J. Lippard and E.T. DelaneySummaryWe present a case study where a new seismic dataset’s improved data quality has enabled a geologically-constrained Bayesian pre-stack inversion algorithm to produce reliable and usable inversion results to uncover significant pockets of oil. The chosen inversion methodology was PCube+: A Bayesian algorithm that uses a local neighborhood approach to perform a one-step inversion to lithology-fluid classes. By using the resulting sand map together with production and well data, areas with remaining reserves can be identified for infill drilling. One such area that was identified led to the drilling of an oil producer that is one of the best performing wells on the Statfjord field in years.
-
-
-
Amplitude Variation with Angle Inversion Based on Propagator Matrix Modelling
More LessSummaryMost existing amplitude variation with angle (AVA) inversions are based on the exact Zoeppritz equation and its linearized approximations. However, such modellings consider the primary (P-wave) waves only and ignore transmission loss, multiples and many other converted wave modes. It means that strict pre-processing is required to satisfy the requirement of the input data to inversions, which is difficult to accomplish. To overcome this problem, a new AVA inversion based on the propagator matrix method of Carcione (PMC) is proposed in this abstract. PMC is derived from the 1D wave equation and can accurately simulate full wave responses within horizontally multi-layered models. For computational accuracy, we use a Bayesian framework to define the augmented function and choose the L-BFGS optimization method to solve it. Through a model test and real data application, it is found that the proposed AVA inversion based on PMC can effectively eliminate transmission loss and internal multiples and helps to provide better S-wave velocity and density estimations.
-