Naturally Fractured Tight Gas Reservoir Detection Optimization
Project Number
DE-AC21-94MC31224
Goal
To detect and characterize the nature of fracture systems in tight gas reservoirs.
Objective: This project applied advance geophysical techniques to characterize fractures in low permeability formations. The primary area of investigation is the Madden Gas Field. The lines of investigation pursued involved examining in some detail the seismic response due to changes in relative fracture density, and/or changes in fracture orientation. Seismic anomalies were then correlated to reservoir characteristics found in wireline log data, oriented core, and production data. The project will develop spatial maps that contain the structure and faults controlling the reservoir over the Madden Gas Field.
Performer(s)
Blackhawk Geosciences, Blackhawk Geometrics, and Lynn, Inc.
Accomplishments (most recent listed first)
The 3-dimensional, 3 component (3D-3C) seismic survey at the Madden gas field site was completed and processing revealed that the survey area encompassed wells that ranged from excellent gas producers to water producers. By locating the survey in this manner, the two seismic data types (multi-azmuth, 3-D P-wave data and the 3-D S-wave data) are available in the same area as the verification information (ie; production information, and geological information from the wells).
This project demonstrated that direct detection of high fracture density zones containing vertical aligned gas-filled fractures is an attainable goal using P-wave seismic data with S-wave calibration data. Azimuth anisotropy is manifest in S-wave data as S-wave splitting (birefringence), and in P-wave multi-azimuth data, when two or more azimuths are compared. From the Madden Field study, commercial gas production has been linked to high fracture density and also to 8-15% P-wave velocity anisotropy, with faster direction parallel to the fractures (core, logs) and the maximum horizontal stress direction. The relationship of P-wave velocity anisotropy to shear wave anisotropy has been demonstrated using mode-converted (P-S) refection data.
Current Status
and Remaining Tasks: This project successfully developed, with field case studies, a methodology to perform azmuthal seismic surveys that yield "productivity" maps of fractured gas reservoirs. This project has been successfully completed and has been closed out. A final report was issued in a CD-ROM format entitled "Detection and Analysis of Naturally Fractured Gas Reservoirs," available through NETL.
