This project will demonstrate the ability of a new seismic technology to image super-deep gas targets across congested production areas of the shallow-water shelf of the Gulf of Mexico (GOM). The technology being tested uses seismic sensor cables that are deployed on the seafloor. Ocean-bottom sensors can be deployed close to platform legs, wellheads, and other obstacles, allowing complete flexibility in placing receiver stations where they will result in optimal imaging. This creates the ability to improve the imaging of super-deep (30,000 ft) geologic targets.

University of Texas at Austin, Bureau of Economic Geology (BEG) , Austin, TX

The objective of this research is to develop and demonstrate a new seismic technology to image super-deep gas targets across the shallow-water portion of the GOM shelf: long-offset, 4-C, OBC seismic acquisition, processing, and interpretation. The long-offset data to be used in this project have source-receiver offsets of up to 10 km, enabling good imaging of targets to depths of 10 km (30,000 ft). These offsets are the largest available in the seismic industry. Using 4-C data enables both compressional (P-P) and converted-shear (P-SV) wavefield images to be made, providing more rock/fluid information than P-P data alone. This project will produce data displays and maps that document the maximum imaging depths and imaging quality of P-P and P-SV data across the GOM shelf. Increased availability and use of long-offset 4-C seismic data can open important new gas plays to the natural gas industry that have not yet been vigorously pursued due to the lack of high-quality, deep-target imaging capability. The driver for this research is the strong push by operators across the northern GOM shelf to define drilling targets at depths of 9 km and more.

Results
The performer has constructed conventional P-P and P-SV (converted shear) images from four component (4-C) stationary ocean-bottom-cable (OBC) data acquired with nine km maximum source-receiver offsets across one congested area on the northern shelf of the Gulf of Mexico. The P-SV images provided important depositional and stratigraphic information that was not obvious on the P-P image. The example showed that the use of OBC/OBS seismic technology is an excellent way to acquire long-offset seismic data for imaging super-deep targets across areas where there are dense congestions of production and engineering structures. In some instances, OBC/OBS technology will be the only option for acquiring long-offset seismic data across such areas. Also, the P-SV data imaged much deeper than many believed possible. The performers documented numerous examples where P-SV images are equal in quality and resolution to P-P images at depths of 20,000 to 26,000 ft across the Gulf of Mexico.

Benefits
New seismic technology is needed to image super-deep gas targets across congested production areas of the shallow-water shelf of the GOM. This project will demonstrate how the limitations of current towed-cable seismic technology can be overcome across this prolific gas trend. This project has the potential to open new gas exploration areas across the GOM shelf and to add significant gas reserves to the U.S. energy base. The technology that is developed can also influence deep gas exploration in basins outside of the GOM.

Summary
Two 4-C OBC surveys will be available to the project covering a combined 9,000 square mile area across the shallow-water GOM shelf that contains a wide variety of deep gas-play possibilities. A wide range of analyses will be done with the 4-C OBC data. Specifically, a variety of prestack data analyses will be conducted to determine how common-conversion-point (CCP) imaging should be done to make P-SV images complement common-midpoint P-P images.

Resolving the problem of CCP binning of negative-offset P-SV data so that the data can be summed with CCP-binned positive-offset P-SV data will be a key focus area of investigation. Negative-offset CCP binning and positive-offset CCP binning results differ significantly when there is a lateral variation in propagation velocity. Such lateral variations will be widespread for deep GOM strata positioned beneath complex salt layers, rotated fault blocks, and shale diapirs.

(December 2008)
All the proposed research work on this project has been successfully completed and the final report is listed below under "Additional Information".

Funding
This project was funded under DOE Solicitation No. DE-PS26-04NT42072.

$985,870

$2,000,000

NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 918-699-2021) 
Bureau of Economic Geology – Dr. Bob Hardage (bob.hardage@beg.utexas.edu or 512-471-1534)

Final Project Report [PDF]

Publications 
Hardage, B.A. Remington, R., DeAngelo, M., and Fouad, K., Imaging deep gas in crowded areas, AAPG Explorer, April 2006, V. 27, No. 4, p. 38.

Hardage, B.A., DeAngelo, M., and Sava. D., Seismic imaging through gas-charged sediment, AAPG Explorer, V. 28, No.3, scheduled for the March 2007 issue.

Hardage, B.A., Sava, D., Remington, R., and DeAngelo, M., Clay content affects multicomponent seismic images, AAPG Explorer, V. 28, No. 4, scheduled for the April 2007 issue.