Subsalt seismic imaging pdf

Seismic imaging is a tool that bounces sound waves off underground rock structures to reveal possible crude oil and natural gasbearing formations. 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. Advances in seismic imaging have changed the way we view salt bodies. Reducing uncertainty in subsalt imaging with gravity and ftg. In the gulf of mexico we first tried several azimuths of seismic to visualise these large salt bodies. Subsalt imaging using 3d prestack depth migration in the. By studying the echoes, petroleum geologists seek to calculate the depth and. 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. Once seen as impenetrable barriers to geophysical probing, many salt structures are now proving to be thin blankets shielding rich reserves. Subsalt seismic illumination study university of houston. 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.

This effort has focused mostly on data processing with special emphasis on. 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. Recent advances and the way forward presented by tim brice, westerngeco contributors. Subsalt imaging by wave equation reflectivity inversion summary. 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. The imaging success of vsp in this study emphasizes its complementary role to surface seismic. In addition, for a subsalt reflection the upcoming wavefield might be postcritically reflected back down at the base salt. This example demonstrates that reverse time migration of multiples might be a promising method for complex subsalt imaging. Seismic technology leading to the first economic subsalt field, expanded abstracts, 65th seg international meeting and exposi. Subsalt imaging for exploration, production, and development. Slower velocities underneath the salt are observed on the sonic log. Improving exploration effectiveness in the subsalt. Implementing imaging algorithms from acoustic to elastic. Velocity model building and seismic imaging of subsalt sedimentary.

Modeling results show that even fullazimuth surface seismic is not able to image steeply dipping subsalt events associated with faults and threeway traps. Figure 4 shows a comparison of seismic subsalt velocities and the sonic log. Hrmt depth imaging clearly defined the top of salt figure 3a and the shallow salt flanks geometries. 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. Geo expro 3d seismic imaging reveals subsalt hydrocarbon. Both imaging enhancements can have a significant business value, and the resulting vsp data sets have demonstrated a clear impact on business decisions. Complex propagation of seismic waves through salt bodies, combined with incomplete acquisition geometry, result in uneven illumination of subsalt targets. Jerry kapoor, nick moldoveanu, chris cunnell, stuart papworth, denis vigh.

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. Isotropic and anisotropic velocity model building for subsalt seismic imaging article pdf available in geophysics 823. Most of the subsalt fourway prospects with gentle dips are well imaged with the. Wins major award from pemex for an integrated subsalt. In seismic exploration, many decisions are based on interpretations of seismic images, which are a ected by multiple sources of uncertainty. Seismic imaging is considered key to reducing uncertainty in oil exploration. Improving the greater k2 area subsalt imaging with. The identification of the target depends on the interpretation of the seismic image.

We turn geophysical data into actionable information. Quantitative application of poststack acoustic impedance. Subsalt imaging in the gulf of mexico has grown increasingly important since it has over 500 salt domes. Thus, the quantitative use of seismic data becomes of paramount importance. Enhancing salt and subsalt imaging in deep water, gulf of. Imaging internal multiples from subsalt vsp data n examples. Seismic imaging technology seismic imaging is considered key to reduce risk and cost in exploratory as well as development drilling. 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. Seismic surveys play an important role in finding the reservoirs, but unfortunately, data quality is often dismally poor. When that showed promise, we moved on to wide azimuth towed streamer seismic, or wats, to maximise the. Lewis, jennifer clinch, simon meyer, dave richards, matt. 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. Specialty algorithms cope with extremes of structure, velocity contrasts and anisotropy while imaging subsalt reservoirs, heterogeneous shale plays and bypassed hydrocarbons in mature fields. Reverse time migration of multiples for subsalt imaging.

Pdf subsalt steep dip imaging study with 3d acoustic. Salt has unusual properties which complicate seismic exploration. In this thesis, i focus on two uncertainty sources that a ect seismic imaging. This has provided keen motivation for improving the seismic product. Only a 3d vsp is able to image targeted subsalt steep dips by placing receivers below the salt. For vintage acquired seismic datasets, modern preprocessing techniques such as deghosting, can add immense value. A geological interpretation of 3d seismic data of a salt. Aside from the water layer, a gulf of mexico velocitydepth model is typically represented in two parts. Subsalt imaging improvements with 29 kms offset test data 2x4 dual coil 2x4 dual coil plus 2x6 test 2x6 dual coil longoffset contribution 23217. Subsalt seismic illumination is a challenge when the salt structure becomes complicated. Fold reduction, due to the low signaltonoise ratio. 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. Pdf isotropic and anisotropic velocity model building. Once seen as impenetrable barriers to geophysical probing, many salt structures are.

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. Seismic imaging technology seismic imaging is considered key to reducing risk and cost in exploratory as well as development drilling. 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. Twoway wave propagation in time based on numerical solution of twoway wave equation. Our internationally acclaimed subsurface imaging centers apply innovative methods to get the most out of potential field, borehole seismic and surface seismic data. Even using the most advanced seismic acquisition and imaging. Pdf subsalt imaging for exploration, production, and development.

Nevertheless, accurate imaging of the basesalt boundary and the subsalt region is only possible by way of prestack depth migration. However, with only a handful of well penetrations and generally poor quality subsalt seismic data, many structural. Pdf the field of subsalt imaging has evolved rapidly in the last decade, thanks in part to the. A step forward in integrated depth imaging advances in seismic imaging have changed the way we view salt bodies. Pdf isotropic and anisotropic velocity model building for. 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. The subsalt velocity derived from subsalt tomography via cor correlates to the sonic velocities significantly better than previously derived subsalt models. 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. Westcott me, leach mc, wyatt kd, valasek pa and branham kl. 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. Even using the most advanced seismic acquisition and imaging technology it is difficult to visualize subsalt targets. The major problem for seismic imaging is caused by longperiod multiples between the airwater interface and the many higlectivity interfaces of the zeit.

Imaging improvements from subsalt 3d vsp acquisitions in the. Viscous seismic wave propagation simulation by using fractional order equation has attracted much recent attention. Existing 2d 2012 coil ftg gravity 2014 csemmt 2015 dual coil seismic 2016. Swells in the thickness of the salt displace subsalt reflection points laterally away from their ideal. 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. W e demonstrate that interferometry of internal multiples can be used to. Interpretation of subsalt converted waves depth imaging. 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. Improved subsalt imaging using tti anisotropy and reverse. Subsalt velocity update using rtmbased dt scan to test the complete subsalt velocity update flow, bp 2d synthetic data set is used. Investigation of deepwater gulf of mexico subsalt imaging. 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. Improved subsalt imaging and salt interpretation by. Many recent advances in seismic imaging technology have been in response to these saltrelated problems obrien.

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. Acquisition experiments for improved subsalt imaging in. In order to constrain the gravity model, seismic velocities were transformed into densities utilizing. Improved subsalt imaging using tti anisotropy and reverse time migration scans duryodhan epili, george cloudy jr. 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.

Tim summers, subsalt imaging technology director for bp, takes up the story. 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. The initial subsalt velocity field is roughly a 1d model as shown in figure 3b. The goal is to enhance the shadow zones in a subsalt seismic image. 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. Subsalt imaging using 3d prestack depth migration in the uk. 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. While the potential yield is great, the salt layer poses unique imaging challenges. The resulting complexity of the seismic wavefields has also challenged traditional velocitymodelbuilding tools and migration algorithms. 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.

Seismic imaging of evaporite bodies is notoriously difficult due to the complex shapes. Seismic imaging of these salt domes is important because salt domes can be sources of sulfur, sources of salt, and, most importantly, petroleum reservoirs. The depth imaging of salt pillow structures was subject to be improved by the integration of gravity, ftg, and mt data interpretation. Seismic modeling study of subsaltimaging problems in the. Previous seismic processing studies had failed to produce a reliable. Seismologists use ultrasensitive devices called geophones to record the sound waves as they echo within the earth. Imaging improvements from subsalt 3d vsp acquisitions in. 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. Efficient, reliable and highquality seismic imaging. Seismic modeling study of subsaltimaging problems in the gulf of suez. Mexico gom to show how fwi can improve imaging in the subsalt.

S247s258 may 2017 with 124 reads how we measure reads. Other large salt dome regions are located in brazil, germany, iran, and iraq. A model study examines some problems encountered in subsalt amplitude analysis and demonstrates that traditional techniques for detecting hydrocarbons and overpressured sediments using. Rev erse time mig r ation of multiples for subsalt imaging. Thus, image uncertainty quanti cation is an important, albeit challenging task.