Subsalt seismic imaging pdf

Cgg announced today that it has been awarded a major contract by pemex to deliver an orthogonal wideazimuth integrated solution designed to optimize subsalt seismic imaging in. S247s258 may 2017 with 124 reads how we measure reads. Improved subsalt imaging using tti anisotropy and reverse. Rtm was introduced about 30 years ago as a 2d poststack depthmigration algorithm mcmechan, 1982. Even using the most advanced seismic acquisition and imaging. Marchenko redatuming allows one to use surface seismic reflection data to generate the seismic response at any point in the subsurface due to sources at the. Subsalt imaging improvement possibilities through a. Most of the subsalt fourway prospects with gentle dips are well imaged with the. This effort has focused mostly on data processing with special emphasis on. In the gulf of mexico we first tried several azimuths of seismic to visualise these large salt bodies. One is the degradation of the image of the steep flanks of the salt body, and the other is the low illumination area underneath the salt flanks. Thus, the quantitative use of seismic data becomes of paramount importance.

This has provided keen motivation for improving the seismic product. Seismic imaging of evaporite bodies is notoriously difficult due to the complex shapes. The goal is to enhance the shadow zones in a subsalt seismic image. The subsalt velocity derived from subsalt tomography via cor correlates to the sonic velocities significantly better than previously derived subsalt models. Seismic imaging is a tool that bounces sound waves off underground rock structures to reveal possible crude oil and natural gasbearing formations. We turn geophysical data into actionable information.

Subsalt imaging by wave equation reflectivity inversion summary. Tim summers, subsalt imaging technology director for bp, takes up the story. Jones 2, zhengzheng zhou, bin wang3, and faqi liu4 abstract the field of subsalt imaging has evolved rapidly in the last decade, thanks in part to the availability of low cost massive computing infrastructure, and also to the development of new. Interpretation of subsalt converted waves depth imaging. For vintage acquired seismic datasets, modern preprocessing techniques such as deghosting, can add immense value.

Reducing uncertainty in subsalt imaging with gravity and ftg. Many recent advances in seismic imaging technology have been in response to these saltrelated problems obrien. Seismic imaging challenges as industry progresses into appraisal and development of deepwater subsalt fields, answers to new and increasingly detailed questions are sought in an effort to minimize risk and optimize project value. Thus, image uncertainty quanti cation is an important, albeit challenging task.

The second article enhancing salt and subsalt imaging in deep water, gulf of mexico, with common offset rtm gathers, by jianshun sheng, seung yoo, cristina retatang and gary rodriguez, is focused on two of the latest processing technologies common offset rtm cor gathers for dirty salt and subsalt velocity tomography update and dual. While the potential yield is great, the salt layer poses unique imaging challenges. Westcott me, leach mc, wyatt kd, valasek pa and branham kl. Fold reduction, due to the low signaltonoise ratio.

Wins major award from pemex for an integrated subsalt. Second, the location of the receivers closer to the imaging targets enables higher frequency content of the resulting vsp data compared to conventional surface seismic images. Pdf isotropic and anisotropic velocity model building for. Improved subsalt imaging and salt interpretation by. The imaging success of vsp in this study emphasizes its complementary role to surface seismic. Once seen as impenetrable barriers to geophysical probing, many salt structures are now proving to be thin blankets shielding rich reserves. Complex propagation of seismic waves through salt bodies, combined with incomplete acquisition geometry, result in uneven illumination of subsalt targets. Acquisition experiments for improved subsalt imaging in.

Twoway wave propagation in time based on numerical solution of twoway wave equation. Imaging improvements from subsalt 3d vsp acquisitions in the. Swells in the thickness of the salt displace subsalt reflection points laterally away from their ideal. Lewis, jennifer clinch, simon meyer, dave richards, matt. Seismic imaging is considered key to reducing uncertainty in oil exploration. Imaging internal multiples from subsalt vsp data n examples. A geological interpretation of 3d seismic data of a salt. Viscous seismic wave propagation simulation by using fractional order equation has attracted much recent attention. Subsalt imaging using 3d prestack depth migration in the uk.

In addition, for a subsalt reflection the upcoming wavefield might be postcritically reflected back down at the base salt. In order to constrain the gravity model, seismic velocities were transformed into densities utilizing. Seismologists use ultrasensitive devices called geophones to record the sound waves as they echo within the earth. The major problem for seismic imaging is caused by longperiod multiples between the airwater interface and the many higlectivity interfaces of the zeit. Subsalt imaging using 3d prestack depth migration in the. Seismic technology leading to the first economic subsalt field, expanded abstracts, 65th seg international meeting and exposi. Subsalt imaging has proven challenging in part because of the complex geometries of the salt canopies, which can yield highly variable illumination on subsalt reflectors. Subsalt velocity update using rtmbased dt scan to test the complete subsalt velocity update flow, bp 2d synthetic data set is used.

By studying the echoes, petroleum geologists seek to calculate the depth and. Pdf the field of subsalt imaging has evolved rapidly in the last decade, thanks in part to the. Imaging internal multiples from subsalt vsp data n examples of targetoriented interferometry ivan v asconcelos 1, roel snieder 2, and brian hornby 3 abstract seismic interferometry has become a technology of growing interest for imaging borehole seismic data. The existing 3d seismic was not suitable to image reflectors in the shallow subsurface, and ambiguities in the allochthonous salt imaging led directly to large uncertainties imaging, depth conversion in the subsalt regions of the model. However, conventional finitedifference fd methods of fractional partial difference equation adopt a global difference operator to. W e demonstrate that interferometry of internal multiples can be used to. A numerical test on the sigsbee2b data set shows that a wider coverage and a more balanced illumination of the subsurface can be achieved by migration of multiples compared with conventional migration of primary reflections. In this thesis, i focus on two uncertainty sources that a ect seismic imaging. Other large salt dome regions are located in brazil, germany, iran, and iraq. Jones1 and ian davison2 abstract seismic imaging of evaporite bodies is notoriously difficult due to the complex shapes of steeply dipping flanks, adjacent overburden strata, and the usually strong acoustic impedance and velocity contrasts at the sedimentevaporite interface. Our internationally acclaimed subsurface imaging centers apply innovative methods to get the most out of potential field, borehole seismic and surface seismic data.

Seismic imaging technology seismic imaging is considered key to reduce risk and cost in exploratory as well as development drilling. When that showed promise, we moved on to wide azimuth towed streamer seismic, or wats, to maximise the. The resulting complexity of the seismic wavefields has also challenged traditional velocitymodelbuilding tools and migration algorithms. Seismic acquisition geometry impacts the seismic image, so in this article we show how advances in imaging deepwater subsalt plays in the deep water gulf of mexico. Once seen as impenetrable barriers to geophysical probing, many salt structures are. Seismic surveys play an important role in finding the reservoirs, but unfortunately, data quality is often dismally poor. Isotropic and anisotropic velocity model building for subsalt seismic imaging article pdf available in geophysics 823. However, with only a handful of well penetrations and generally poor quality subsalt seismic data, many structural. Reverse time migration of multiples for subsalt imaging. Geo expro 3d seismic imaging reveals subsalt hydrocarbon.

A geological interpretation of 3d seismic data of a salt structure and subsalt horizons in the mississippi canyon subdivision of the gulf of mexico a thesis submitted to the graduate faculty of the university of new orleans in partial fulfillment of the requirements for the degree of master of science in geology by mariela cecilia mejias f. Subsalt imaging for exploration, production, and development. Seismic modeling study of subsaltimaging problems in the. Imaging improvements from subsalt 3d vsp acquisitions in. Both imaging enhancements can have a significant business value, and the resulting vsp data sets have demonstrated a clear impact on business decisions. Pdf subsalt steep dip imaging study with 3d acoustic. Salt has unusual properties which complicate seismic exploration. Improving exploration effectiveness in the subsalt. Velocity model building and seismic imaging of subsalt sedimentary. Enhancing salt and subsalt imaging in deep water, gulf of.

Quantitative application of poststack acoustic impedance. The identification of the target depends on the interpretation of the seismic image. Efficient, reliable and highquality seismic imaging. Mexico gom to show how fwi can improve imaging in the subsalt. Seismic modeling study of subsaltimaging problems in the gulf of suez. Improving the greater k2 area subsalt imaging with advanced seismic acquisition, model building, and imaging technologies a gulf of mexico case study abay aibaidula, david walraven, and arnold rodriguez. Seismic imaging technology seismic imaging is considered key to reducing risk and cost in exploratory as well as development drilling. The link between seismic acquisition and the final image became apparent, particularly as the industry moved from predominantly 2d to 3d data and from time imaging to depth imaging. Modeling results show that even fullazimuth surface seismic is not able to image steeply dipping subsalt events associated with faults and threeway traps. Rev erse time mig r ation of multiples for subsalt imaging. To simplify the testing, only one out of four shots is used, and the offset is reduced to 8 km from the original 15 km. Investigation of deepwater gulf of mexico subsalt imaging. Figure 4 shows a comparison of seismic subsalt velocities and the sonic log.

Depth imaging one of the main developments in the past fewyears in the area of depth imaging is the routine use of 3d commonshot rtm as the leading algorithm for imaging of both marine and land seismic data fletcher et al. This example demonstrates that reverse time migration of multiples might be a promising method for complex subsalt imaging. Previous seismic processing studies had failed to produce a reliable. Improving the greater k2 area subsalt imaging with. During the past few years, advances in both acquisition and imaging technologies have provided unprecedented breakthroughs for subsalt imaging in terms of image quality as well as velocity model accuracy. Subsalt imaging improvements with 29 kms offset test data 2x4 dual coil 2x4 dual coil plus 2x6 test 2x6 dual coil longoffset contribution 23217. Existing 2d 2012 coil ftg gravity 2014 csemmt 2015 dual coil seismic 2016. Subsalt imaging using 3d prestack depth migration in the uk southern north sea the challenge for a reservoir in an area containing one of the largest salt structures in the southern north sea, accurate depth mapping was vital for the assessment of potential gas prospectivity. Seismic imaging of these salt domes is important because salt domes can be sources of sulfur, sources of salt, and, most importantly, petroleum reservoirs.

Nevertheless, accurate imaging of the basesalt boundary and the subsalt region is only possible by way of prestack depth migration. In the early 1990s petroleum industry analysts had begun to refer to the gulf of mexico as the dead sea, claiming that there were no more large undiscovered resources left offshore magazine, 1997. Pdf isotropic and anisotropic velocity model building. Pdf subsalt imaging for exploration, production, and development. In conclusion, with the inherent difficulties in subsalt imaging, we are able to show the value of a multifaceted approach to providing uplift in the subsalt image. Interpretation of subsalt converted waves as expected from analyzing real datasets, two typical problems can be seen on the presdm results of both the acoustic and elastic modeled data. Quantitative application of poststack acoustic impedance inversion to subsalt reservoir development t he cost and complexity of deepwater subsalt development wells is so great that a very limited spatial sampling of the target reservoir is achievable with well data. Summary hybrid inversion of gravity data can improve seismic imaging of the subsalt able to recover sharp boundary using constrained voxel based inversion fast, flexible and iterative seamless integration within the seismic workflow reduces uncertainty and produces an improved model for exploration potential beyond base of salt inversion of gravity gradient and magnetic. Improved subsalt imaging using tti anisotropy and reverse time migration scans duryodhan epili, george cloudy jr. Only a 3d vsp is able to image targeted subsalt steep dips by placing receivers below the salt. Even using the most advanced seismic acquisition and imaging technology it is difficult to visualize subsalt targets.

Subsalt seismic illumination study university of houston. A background velocity field with vertical velocity variations characterized by gentle variations in the gradient, the absence of distinct layer boundaries, and mildtomoderate lateral velocity variations tabular and diapiric salt bodies with different shapes, but with a constant velocity. Specialty algorithms cope with extremes of structure, velocity contrasts and anisotropy while imaging subsalt reservoirs, heterogeneous shale plays and bypassed hydrocarbons in mature fields. Subsalt seismic illumination is a challenge when the salt structure becomes complicated. Hrmt depth imaging clearly defined the top of salt figure 3a and the shallow salt flanks geometries. Subsalt imaging in the gulf of mexico has grown increasingly important since it has over 500 salt domes. Jerry kapoor, nick moldoveanu, chris cunnell, stuart papworth, denis vigh. Improving the greater k2 area subsalt imaging with advanced seismic acquisition, model building, and imaging technologies a gulf of mexico case study abay aibaidula, david walraven. A step forward in integrated depth imaging advances in seismic imaging have changed the way we view salt bodies.

Aside from the water layer, a gulf of mexico velocitydepth model is typically represented in two parts. The depth imaging of salt pillow structures was subject to be improved by the integration of gravity, ftg, and mt data interpretation. Implementing imaging algorithms from acoustic to elastic. Slower velocities underneath the salt are observed on the sonic log. Advances in seismic imaging have changed the way we view salt bodies. In seismic exploration, many decisions are based on interpretations of seismic images, which are a ected by multiple sources of uncertainty. The initial subsalt velocity field is roughly a 1d model as shown in figure 3b. Recent advances and the way forward presented by tim brice, westerngeco contributors. Investigation of deepwater gulf of mexico subsalt imaging using anisotropic model, data set and rtm tempest fatmir hoxha 1, jacqueline oconnor1, jeff codd, david kessler, alex bridge2, dana jurick 2, richard brietzke, and kenneth beeney2 abstract performing accurate depthimaging is. A model study examines some problems encountered in subsalt amplitude analysis and demonstrates that traditional techniques for detecting hydrocarbons and overpressured sediments using.