Unconventional reservoirs have become important hydrocarbon objectives for oil and gas companies. Although advances in drilling technology have been the primary factors in achieving economic viability in these tight reservoirs, 3D seismic data has played an increasingly important role in development success.
Due to their low permeability, economic production in tight reservoirs can only be achieved through hydraulic fracture stimulation. Thus, a key factor in economic success is the ability to create as extensive and complex a fracture network as possible. The extent of the fracture network created during hydraulic stimulation is strongly affected by the in-situ stress field, the natural fracture systems present, and the geo-mechanical properties of the reservoir. Initially, seismic data was considered to be of little use, however, over time operators have realized that 3D seismic data can provide significant value by helping to optimize the results obtained from horizontal drilling and hydraulic stimulation.
Unequal horizontal stresses and vertical aligned fractures can cause seismic velocities and amplitudes to vary with source-receiver azimuth. Azimuthal analysis of wide azimuth 3D seismic data allows the measurement of the variation in velocity and amplitude with azimuth and provides information about stress fields and natural fracture systems. Meanwhile, seismic inversion enables the estimation of important geo-mechanical properties of the reservoir such as brittleness and closure stress which strongly influence the results obtained from hydraulic fracture stimulation.
Accounting for the effects of anisotropy as well as geologic dip in P-wave data processing can significantly improve the quality of the seismic image and estimation of stress fields, natural fracture systems and reservoir properties. Both VTI and HTI anisotropy need to be taken into account for optimal imaging. A new anisotropic imaging technique utilizing OVT PSTM incorporating both HTI and VTI information into the migration process results in a much improved seismic image and more accurate anisotropy attributes. The effectiveness of this technique will be demonstrated with field data examples from an unconventional resource play.
Edward Jenner – Manager, Research and Development, graduated from Birmingham University, UK with a B.Sc. in Physics with Astrophysics and from Leeds University, UK with a Masters in Geophysics. In 2001 he completed his Ph.D. in Geophysics at the Colorado School of Mines in Azimuthal velocity and AVO analysis. Since 2002 Edward has been manager of land research and development for ION with particular interests in the areas of anisotropy, AVO and imaging. Prior to 2001, Edward worked for BP investigating amplitude preserving multiple removal, at Conoco working on statics and pre-stack depth imaging and at CGG developing a technique for converted wave pre-stack depth migration. In 2003, Edward was awarded the SEG Clarence Karcher Award for his work in the field of azimuthal anisotropy.