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Collaborating Authors
Results
3-D Imaging of Seismic Data From a Physical Model of a Salt Structure
Roberts, Peter (Seismic Research Center, Los Alamos National Laboratory) | House, Leigh (Seismic Research Center, Los Alamos National Laboratory) | Huang, Lian-Jie (Seismic Research Center, Los Alamos National Laboratory) | Wiley, Robert (University of Houston) | Sekharan, K.K. (University of Houston)
Summary Seismic data from a physical model of the SEG/EAGE salt structure were migrated to test imaging of this complex structure and to benchmark imaging codes. The physical model was constructed at the University of Houston from a scaled-down rendition of the SEG/EAGE salt structure. Two simulated marine surveys were collected from it: one was a conventional towed streamer survey, the other a vertical receiver cable survey. The towed streamer data set is the focus of this study. 2-D prestack depth migrations were done to establish that imaging with a subset of data from a line provides a reliable and adequate image. A 3-D prestack depth migration of one line provides a better image than the 2-D image and improved imaging of some features than to the 2-D images.
Summary Three-dimensional modeling data are useful for validating 3-D processing algorithms (e.g. migration, velocity analysis, multiple suppression, etc.), understanding wave propagation in a complex 3-D medium, choosing proper acquisition parameters, and testing various data compression and transmission techniques. The availability of 3-D modeling data online would be a great advantage to both the oil industry and academia. The well-known SEG/EAGE 3-D numerical modeling data sets used to be accessible from Lawrence Livermore National Laboratory (LLNL) via the World Wide Web (1). The Allied Geophysical Laboratories (AGL), University of Houston, is considering providing similar services. This project aims at exploring approaches to data uploading, extraction, and transmission.
- Geophysics > Seismic Surveying > Seismic Processing (0.55)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.55)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
ABSTRACT No preview is available for this paper.
Abstract A physical model similar to the SEGIEAGE numerical salt model was constructed to study the problems and issues of acquiring and processing seismic data over geological situations involving salt and subsalt layers. A large 3D dataset acquired simulating vertical cable is composed of 8 swaths with 8 cables with 8 transducers in each cable to produce truly 3D Common Cable Gathers (CCG) that were processed through pre-stack depth migration. The final image is composed of the stack of all CCG migrated including both upcoming and down-going wave fields. Partial images obtained from stack of depth volumes of each field separately show that down-going field data had reflections with more continuity and higher SIN ratio than the up-coming waves in parts with non-steep dips. The up-coming, however, did a better job in the flanks of the salt. Separation of the up-coming and downgoing fields to different datasets for separated migration did not result much difference in the final image. The general results have been showing that vertical cable technique is an excellent tool to obtain depth image of complex geologic structures. The power of stacking migrated images of different hydrophones and cables with different illuminations increase tremendously the signal-to-noise ratio of the depth image resulting In a more reliable information of the subsurface. Introduction Imaging geological structures beneath salt is still a great challenge and even the most current conventional acquisition equipment and sophisticated processing techniques used to obtain the Image of these structures fails to provide reliable results. In order to understand the issues involved in acquiring and processing seismic data over such areas, a physical model Similar to SEG/EAGE numerical model (I) was constructed (funded by Marathon Oil Co and Louisiana Land and Exploration) at the Allied Geophysical Laboratories of the University of Houston (2). The model consisted of a complex salt block with a canopy, toe faults and rugose surface at the top, surrounded by sedimentary layers and a three dimensional structure beneath the salt. A conventional 3D marine data set consisting of nearly 20 million traces was acquired over this model. A different approach to conventional 3D data acquisition was used. Vertical cables anchored at the bottom of the ocean while a source boat shot a regular grid over the surveyed area (3) were simulated. This technique of seismic data acquisition has been seen as an excellent method for exploration of different types of prospects, (4), (5), (6) and (7) especially for deep water and areas where the conventional streamer is unable to obtain coverage. We simulated this different approach to acquire data over the SEGIEAEG physical model. The model and a detailed acquisition scheme description were presented last year (8). In this paper we will show the procedures used in processing the data through pre-stack depth migration and present the results. Acquisition The data were acquired in the beginning of 1997. Basically 8 cables were deployed in each of four areas of the model. In each area, two shot patches displaced by 25 m in both × and y direction of 99 lines and 165 shots spaced at 50 m apart, were carried out (fig. 1).
3D Marine Data Acquisition and Processing over ACTI/EAGE Physical Model Using Vertical Hydrophone Cables
Sekharan, K.K. (University of Houston ) | Guimareas, M.G. (University of Houston ) | Jackson, R.A. (University of Houston ) | Ebrom, D.A. (Texaco, Inc. ) | Krall, P. (Texaco, Inc. ) | Sukup, D. (Texaco, Inc. )
Abstract Imaging geological structures beneath salt is a great challenge. Since the presence of commercially viable hydrocarbon deposits has been confirmed below salt structures, especially in the Gulf of Mexico, imaging subsalt structures has added significance. However, massive amounts of three dimensional marine data have to be acquired and processed to image these complex subsalt structures. To understand the problems and issues in acquiring and processing three dimensional offshore marine data, a physical model (funded by Marathon Oil Co. and Louisiana Land and Exploration) was constructed at the Allied Geophysical Laboratories of the University of Houston. The model is imilar to the SEG/EAGE numerical salt model consisting of a complex salt block with a canopy, toe faults, and a rugose surface at the top. There is a three dimensional layer underneath the salt. The salt is surrounded by severalsedimentary layers. A conventional 3D marine data set (1) consisting of nearly 20 million traces was acquired (funded by DOE and 11 companies) over this model. Several groups are processing this data set separately through pre-stack depth migration. A different approach to conventional marine acquisition is the use of vertical cables anchored at the bottom of the ocean, and a boat pulling just the source. This method acquires a significantly different data set. The acquisition of a 3D data set over the SEG/EAGE physical model using vertical cable simulation is in progress. This project will be a direct comparison of conventional versus vertical cable acquisition and processing of marine 3D data. The results will be presented. Introduction Imaging geological structures beneath salt is a great challenge. Since the presence of commercially viable hydrocarbon deposits has been confirmed below salt structures, especially in the Gulf of Mexico, imaging subsalt structures has added significance. However, massive amounts of three dimensional marine data have to be acquired and processed to image these complex subsalt structures. In conventional 3D marine data acquisition several closely spaced 20 lines are acquired. The boat has to pull long receiver cables and hence travel a long distance beyond the area of coverage. The data are of narrow azimuth and subject to the surface conditions of the water. Vertical cable acquisition has many advantages over the conventional method. In the acquisition phase, a considerable savings of time and money arises since smaller boats could pull the source, eliminating the large distances required for turns. Coverage is better since the boats can be closer to any obstructions in the survey area. Vertical cables anchored at the ocean bottom surface is less susceptible to weather conditions at the water surface. Wide azimuth data is obtained (2), and 3D pre-stack migration is very cost effective. The vertical cable acquisition method is a patented method for acquiring and processing pre-stack 3D marine seismic data (3). It is a less mature technique and, therefore, a large number of problems remain to be solved as the technique is developed. The physical model project presented in this paper provides an opportunity to understand not only the merits of this technique but also the problems associated with it.
- North America > United States > Texas (0.29)
- North America > United States > Louisiana (0.24)
- North America > United States > Illinois > Madison County (0.24)
The target structure was made of white silicone rubber and had four embedded stainless steel In 1995, the Allied Geophysical Laboratories rods. Five sets of 3-D data were acquired over the conducted a project on physical modeling of the model in water tank, and acquisition was set to subsalt imaging problems. Imaging the targets simulate marine seismic work (Sekharan et.
These data would provide a test data for standard processing algorithms and for most techniques being Recent drilling has confirmed both significant reservoir developed. It was felt that the physical model could be potential and the presence of commercial hydrocarbons produced and the data acquired at a fraction of the cost of below salt structures in the Gulf of Mexico. Obtaining the numerical model data set. The model would be fully 3-definite seismic images with standard processing schemes D, support converted shear waves, and data acquisition beneath these salt structures is very difficult if not would closely correspond to current techniques.
- North America > United States (0.36)
- North America > Mexico (0.35)
Abstract The application of three-dimensional (3-D) seismic methods to reservoir characterisation has gained wide acceptance in the last ten years. Almost seventy-five percent of additional reserves are now found in mature areas by redefining reservoir boundaries and internal heterogeneities using surface and crosswell seismic methods. However the implementation of, in particular, 3-D seismic methods can be very expensive and can rival the cost of drilling a dry hole. A solution to the problem is to physically model a reservoir in the laboratory and to collect simulated seismic reflection data over the model. Then conventional, or unconventional, seismic processing techniques can be applied to the data prior to embarking on costly field seismic data collection. The physical modelling experiments enable an improved and corrected image of the subsurface to be developed, and a more effective drilling program to be designed. We briefly review the 3-D seismic method and indicate its value in reservoir characterisation. Examples will be given of models developed for experiments in fault plane analysis and for imaging beneath high velocity near surface layers. Introduction The 3-D seismic method was first shown to be viable for subsurface imaging in the early 1970s (Ref. 1). This was the first successful application of physical modelling to solving 3-D seismic problems. The fact that the 3-D method has been rapidly accepted in the last 10 years has been documented (Ref. 2). The conclusion is that '3-D seismic surveys have become a cost-effective tool for mapping hydrocarbon reservoirs and can have a major impact on the volume of reserves estimated'. The method needs the subsurface area of interest to be spatially sampled correctly with seismic traces. in marine operations this may be achieved with a ship towing many cables, such that each source and receiver combination represent a sample point. In land operations various positionings of sources and receivers may be used such that an area of the subsurface is 'covered' with seismic traces. The examples in this paper show two very different applications of 3-D seismic to solving reservoir problems, both of which required the extensive application of physical models. Fault Plane Analysis. When a seismic wave meets an acoustic contrast it may be reflected and/or refracted. If a wave reaches a fault with a relatively high impedance contrast across it, it will refract through the fault plane, resulting in a change in the travel path of the wave. When common midpoint gathers are produced, the wave refracting across the fault can cause changes in the trace gathers which can affect 'reflections' within the gather. When the data are stacked the result can give a different appearance to the image. Such a change could be the presence of an apparent fault at depth, which is in fact an artefact of the stacking process. When computing the reserves in a reservoir the assumption of the presence of such a fault could lead to incorrect reserve estimates. Consequently, it is very important to determine whether such an artefact does, or does not, exist. Two dimensional (2-D) seismic data collected across a fault plane containing such an impedance contrast in the shallow section will produce a false image of a fault (Ref. 3). 3-D data collected along strike to the fault will not have raypaths passing through the fault plane. so these data will not create such an artefact. A 2-D section can be reconstituted from the 3-D data, along the plane of the original 2-D line, without the artefact indicating that the 'fault' does not exist. P. 81
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (1.00)
- Geophysics > Seismic Surveying > Seismic Processing > Seismic Migration (0.48)
- Oceania > Timor-Leste > Timor Sea > Bonaparte Basin > Oliver Field (0.99)
- Oceania > Australia > Western Australia > North West Shelf > Browse Basin > Block WA-315-P > Plover Formation (0.99)
- Oceania > Australia > Western Australia > North West Shelf > Browse Basin > Block WA-274-P > Plover Formation (0.99)
- (2 more...)
Abstract Recent drilling has confirmed both significant reservoir potential and the presence of commercial hydrocarbons below salt structures in the Gulf of Mexico, Obtaining definitive seismic images with standard processing schemes beneath these salt structures is very difficult if not impossible. Because of the complicated seismic behavior of these structures, full volume 3-D prestack depth migration is required l. Unfortunately, carrying out the multitude of calculations needed to create a proper image requires the largest and fastest supercomputers and rather complex numerical algorithms. Furthermore, developing and testing the imaging algorithms is quite involved and requires appropriate test data sets, To better understand the problems and issues of sub salt imaging, Marathon Oil Company and Louisiana Land and Exploration Company contracted with the University of Houston's Allied Geophysical Laboratories (AGL) (o construct a "salt canopy" physical model. The model is patterned after the SEG/EAEG Salt Model and is made from synthetic materials. his a full three-dimensional model with an irregularly shaped, lateral salt structure embedded in five distinct ‘sedimentary’ layers. The model was used to acquire a multi-offset 3-D marine style survey. These data are being used to address problems of sub salt imaging. In addition to standard processing techniques, we will be investigating algorithms for multiple removal and prestack depth migration. Introduction Recent exploration and subsequent drilling in the Gulf of Mexico has demonstrated significant reservoir potential below salt structures. Conventional seismic methods fail to image beneath salt structures because of the complex nature of the salt body and the high velocity contrast at the salt-sediment interface. Imaging beneath salt requires full volume 3-D prestack depth migration (Ratcliff et al 1992). The development of these algorithms is involved and requires appropriate test data. Numerical modeling has frequently been used to provide data for test algorithms and to provide insights into seismic wave propagation. The SEC research committee developed a salt model which used to obtain synthetic seismic data, Finite difference modeling was used to compute the seismic response of this model. These data can be used to provide insight into sub At the same time, Marathon Oil Company and Louisiana Land and Exploration proposed a physical model for the acquisition of a conventional marine seismic data set. These data would provide a test data set for standard processing algorithms and for most techniques being developed. It was felt that the physical model could be produced and the data acquired at a fraction of the cost of the numerical model data set. The model would be fully 3-D, support shear waves, and data acquisition would closely correspond to current techniques. Model Design The basic design of the physical model came from the SEG /EAEG numerical model. A cross-section of the physical model is shown in Figure 1. The sediments in the SEG /EAEG model contain curved interfaces and a vertical velocity gradient. The physical model has flat horizons and the constant velocity layers. Also the physical model does not have the shale sheath, the sub salt lenses or the over-pressure region.
- Asia > Middle East > Yemen (1.00)
- Asia > Middle East > Saudi Arabia (1.00)
- Africa > Sudan (1.00)
- (4 more...)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.55)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.34)
- Asia > Middle East > Saudi Arabia > Red Sea > Red Sea Basin (0.99)
- North America > Cuba > Gulf of Mexico (0.89)
Abstract Recent drilling has confirmed both significant reservoir potential and thepresence of commercial hydrocarbons below salt structures in the Gulf ofMexico, Obtaining definitive seismic images with standard processing schemesbeneath these salt structures is very difficult if not impossible. Because ofthe complicated seismic behavior of these structures, full volume 3-D prestackdepth migration is required l. Unfortunately, carrying out the multitude ofcalculations needed to create a proper image requires the largest and fastestsupercomputers and rather complex numerical algorithms. Furthermore, developingand testing the imaging algorithms is quite involved and requires appropriatetest data sets, To better understand the problems and issues of sub salt imaging, Marathon OilCompany and Louisiana Land and Exploration Company contracted with theUniversity of Houston's Allied Geophysical Laboratories (AGL) (o construct a"salt canopy" physical model. The model is patterned after the SEG/EAEGSalt Model and is made from synthetic materials. his a full three-dimensionalmodel with an irregularly shaped, lateral salt structure embedded in fivedistinct ‘sedimentary’ layers. The model was used to acquire a multi-offset 3-D marine style survey. Thesedata are being used to address problems of sub salt imaging. In addition tostandard processing techniques, we will be investigating algorithms formultiple removal and prestack depth migration. Introduction Recent exploration and subsequent drilling in the Gulf of Mexico hasdemonstrated significant reservoir potential below salt structures. Conventional seismic methods fail to image beneath salt structures because ofthe complex nature of the salt body and the high velocity contrast at thesalt-sediment interface. Imaging beneath salt requires full volume 3-D prestackdepth migration (Ratcliff et al 1992). The development of these algorithms isinvolved and requires appropriate test data. Numerical modeling has frequently been used to provide data for test algorithmsand to provide insights into seismic wave propagation. The SEC researchcommittee developed a salt model which used to obtain synthetic seismic data, Finite difference modeling was used to compute the seismic response of thismodel. These data can be used to provide insight into sub At the same time, Marathon Oil Company and Louisiana Land and Exploration proposed a physicalmodel for the acquisition of a conventional marine seismic data set. These datawould provide a test data set for standard processing algorithms and for mosttechniques being developed. It was felt that the physical model could beproduced and the data acquired at a fraction of the cost of the numerical modeldata set. The model would be fully 3-D, support shear waves, and dataacquisition would closely correspond to current techniques. Model Design The basic design of the physical model came from the SEG /EAEG numerical model.A cross-section of the physical model is shown in Figure 1. The sediments inthe SEG /EAEG model contain curved interfaces and a vertical velocity gradient. The physical model has flat horizons and the constant velocity layers. Also thephysical model does not have the shale sheath, the sub salt lenses or theover-pressure region.
- North America > United States > Louisiana (0.55)
- North America > United States > Illinois > Madison County (0.24)