Combining P-Wave and S-Wave Seismic Data to Improve Prospect Evaluation

Abstract
This report presents three types of evidence documenting that the combination of P-wave and S-wave seismic data provides geologic insights that cannot be provided by conventional P-wave data alone. The study consists of three parts: (1) the basic physics and research findings related to P and S seismic wavefield behavior, (2) the application of the research findings to field-recorded 2-D P and S data to site successful wells, and (3) recommended hydrocarbon plays in Texas where P and P seismic data should be acquired, to better evaluateĀ  reservoir systems andĀ to reveal new hydrocarbon accumulations. Significant advantages accrue when oil and gas prospects and potential infield drill sites are evaluated with both compressional wave (P-wave) and shear wave (S-wave) seismic data rather than with P-wave data only. This report presents three types of evidence documenting that the combination of P-wave and S-wave seismic data provides geologic insights that cannot be provided by conventional P-wave data alone: 1. Field tests and laboratory measurements made on rock samples that show that distinct rock facies can be identified more reliably by combining P-wave velocity (Vp) data with S-wave velocity (V,) data than they can be by using P-wave velocity information only. 2. Examples of two-dimensional (2-D) seismic data that illustrate that combining spatially coincident P-wave and S-wave reflection images helps identify rock types, fluid boundaries, and sequence relationships that cannot be easily inferred from P-wave seismic images only. 3. Examples of seismic detection and mapping of fractured reservoirs by using the dual S-wave images that result from S-wave splitting, a phenomenon that occurs when an S-wave interacts with fractured rock. This wave-splitting phenomenon is unique to S-waves; it does not occur in P-waves. This report consists of three parts: part 1 describes the basic physics and research findings related to P and S seismic wavefield behavior; part 2 illustrates how these research findings have been applied to field-recorded 2-D P and S data to site successful wells; and part 3 describes hydrocarbon plays in Texas where P and S seismic data should be acquired to better evaluate reservoir systems and to reveal new hydrocarbon An important point to emphasize is that the P and S data included in this report are only 2-D seismic profiles. The value of combined P and S seismic imaging for prospect evaluation will increase many fold, compared with the value of the 2-D profiles shown in this report, if the P and S data are recorded, displayed, and interpreted as a 3-D geometry instead of as 2-D data. There is no unsolvable technical barrier that prevents three-component (3-C) seismic data from being acquired, processed, and interpreted in a three-dimensional (3-D) geometry. However, in the present economic climate, seismic contractors hesitate to make the financial investments required to offer three-component and three-dimensional (3C3D) technology services to the industry. This report provides information to the end users of seismic technology--those persons who evaluate and manage oil and gas prospects, particularly those prospects on properties in the State of Texas--so that this user community can then approach seismic contractors and assure them that there will be a market for 3C3D seismic services. This market assurance will be required before 3C3D seismic technology becomes a common commercial service. In addition to creating user demand for 3C3D technology, this report describes those geological conditions in which the combined use of P and S seismic data will provide operators the greatest benefit, and it illustrates where some of these types of reservoir conditions exist in Texas. The Texas-based plays and trends offered as examples of where 3C3D technology should be applied (figs. 36 and 37) were selected on the basis of the following premises: 1. If a correct understanding of subsurface structure is the key to successful drilling in the play or trend, then S-wave data are not needed because 3-D P-wave data alone can define structure. 2. If successful drilling depends on locating fractures, detecting porosity trends, mapping lateral facies variations, or defining subtle stratigraphic traps, then combining S-wave seismic data with P-wave data will be invaluable and is strongly encouraged.
Authors
Bob A. Hardage
Citation

Hardage, B. A., 1996, Combining P-Wave and S-Wave Seismic Data to Improve Prospect Evaluation: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 237, 47 p.

Code
RI237
ISSN
2475-367X
Number
237
Number of figures
37
Number of pages
47
Publisher
The University of Texas at Austin, Bureau of Economic Geology
Series
Report of Investigation
Year
1996