Wafik B. Beydoun

The paraxial ray method

The paraxial ray method is an economical way of computing approximate Green’s functions in heterogeneous media. The method uses information from the standard dynamic ray‐tracing method to extrapolate the seismic wave field at receivers in the neighborhood of a ray so that two‐point ray tracing is not required. Applicability conditions are explicit: they define where asymptotic (high‐frequency) methods are valid, and how far away from the ray the extrapolation remains accurate. Increasing the density of the ray fan improves accuracy but increases computation time. However, since reasonable accuracy is obtained with relatively few rays, the method yields results similar to the two‐point ray‐tracing method, but at a fraction of the cost. Examples of wave‐field extrapolation from a ray to neighboring receivers show that traveltime extrapolation is more accurate than amplitude extrapolation. Accuracy, robustness, and efficiency tests, comparing paraxial ray synthetic seismograms with acoustic finite‐difference...

AVO Migration And Inversion: Are They Commutable?

With the increasing ambition of characterizing hydrocarbon traps in more subtle or complex reservoirs, Amplitude Variation with Offset (AVO) techniques are becoming a valuable seismic tool for quantitative seismic discrimination of lithologies and fluids. One of the biggest remaining challenges is to acquire and process the data in an amplitude preserved fashion and in multi-dimensional geology. This study is a component of this puzzle, and attempts to address the following processing question: what are the benefits of prestack migration before AVO inversion (process 1) versus performing an AVO inversion followed by a poststack migration (process 2)? The comparison is done on a 2-D synthetic model which is valid for process 2. The technique used for process 1 is the prestack depth AVO migration/inversion described in the text which estimates reflectivities and incidence angles in multi-dimensions from the data prior to AVO inversion. Process 2 results are derived using a commercial seismic processing software package.

Geophysical challenges and opportunities of the deepwater Angolan offshore

Recent giant field discoveries on the western edge of the Lower Congo Basin have triggered new opportunities for Tertiary plays offshore Angola. These discoveries have also ratified the impact of 3-D seismic in deepwater prospect evaluation and field development, especially now that drilling and production in water depths of 500 m and more are no longer an obstacle. This paper highlights some of the key challenges and opportunities that would increase the use of geophysics.

Identification of reservoir limits integrating seismic and fluid flow responses

This study attempts to demonstrate on a synthetic sand lens reservoir model that the range of possible reservoir geometries derived from the seismic image is a valid physical constraint in the reservoir response. The aim is to verify that the single phase well test response is sensitive to modifications of the reservoir boundaries derived from a poststack seismic depth image, all the other variables being fixed. The potential benefit of using this method is to enhance reservoir appraisal. This study aims at linking seismic subsurface images to reservoir fluid flow simulations to enhance reservoir appraisal. Petrophysical characteristics are determined from geology, well logs and laboratory measurements. Reservoir possible limits are inferred from seismic depth images. Then, the dynamic response of the reservoir is computed using a numerical fluid flow simulator. Matching observed and ca l cu la ted dynamic responses w i th in th i s mult id iscipl inary framework enables a consistent identification of the reservoir limit.

Introduction to the special section: West African renaissance?

This issue contains a special section on West Africa. A straightforward and fair question to ask is: Why focus on this specific region of the world? Being in Angola for the past two years and having lived some time ago in Nigeria for six years are my (WB) personal basis for attempting to address this question. But before going any further, let us start by expressing our satisfaction at participating as co‐guest editors to this issue dedicated to one of the hottest topics in the petroleum industry today.

Geophysical Challenges & Opportunities of the Deep Water Angolan Offshore

SUMMARY Recent giant field discoveries on the Western edge of the Lower Congo Basin have triggered new opportunities for Tertiary plays offshore Angola. The impact of 3D seismic in evaluating prospects, then in appraising and in developing such fields is now clear. This is further emphasized as drilling and production in deep waters (>500 m) are no longer an obstacle. The purpose of this paper is to capture this impact by highlighting some of the key challenges and opportunities that would increase the us e of geophysics. Efficient evaluation of prospects in the deep and ultra deep Angolan offshore is accomplished by first adapting and then streamlining seismic acquisition, processing and interpretation technologies. Examples illustrate, for instance, the increasing interest in preserving amplitudes, improving seismic resolution, and in subsalt imaging.

International Geophysical Conference and Exposition: 7–10 July 1997, Istanbul, Turkey

His father was the sea‐god Poseidon, and his mother was the golden‐haired Keroessa — daughter of omnipotent Zeus and of his tormented mistress Io. Named after the nymph Byzia, who nursed him at birth, Byzas became king of Megaris and won the heart of Phidalia, daughter of the king of Hellespont. To find the ideal place to build a new city for himself and his bride, Byzas consulted the oracle at Delphi who told him to select a place across “the city of the blind.”

IAC to strengthen ties among geophysicists worldwide

What is the impact of exploration geophysics on international relations? This is a timely question to pose in this, the first special issue devoted to a particular region of the world: Latin America. And I will address it by describing how the SEG International Affairs Committee (IAC) plans to lead various initiatives to ensure, both, that the impact is favorable and beneficial for all involved.

Elastic Migration/inversion of Three-component Seismic Data From the Springdale Reef

Explorationists have always known that S waves were wntributing to the noise in reflection images. Nevertheless, acoustic techniques were (and are) used in the name of computational speed or inadequate data (i.e., only vertical component data). Here we describe an elastic inversion technique and demonstrate its use on a reef target. Offset VSP is an excellent demonstration of the need for elastic inversion techniques because of the large number of converted waves in the data. Elastic inversion also puts some urgency on the need for good S wave velocities. The results are worth the small additional effort. In the example presented, we begin to see some details in the reef, whereas the surface reflection data and conventionally processed VSPs show only the nature of the B Salt/AZ Carbonate interface. This interface is not the reservoir at all and is only crudely related to the reservoir.