High-resolution microseismic imaging

Abstract

We examine the feasibility of high-resolution microseismic imaging of unconventional reservoirs. Given frequencies in typical downhole microseismic data that are almost an order of magnitude higher than in seismic reflection data, a comparable increase in image resolution might be expected, bringing potential resolution of downhole microseismic images to a few meters. We demonstrate that such a resolution is indeed achievable and present two case studies illustrating the reservoir features that can be imaged. Our first example, constructed with P-waves recorded in the Woodford Field, reveals internal fabric of the Woodford reservoir and formations surrounding it, allowing us to discriminate the stimulated and unstimulated zones of the Lower Woodford Shale. Encouraged by those results, in our second example, this time from the Bakken Field, we use the slow shear waves, which are more sensitive to fluids than P-waves, to find out whether hydraulic fractures themselves could be imaged. Our seismic volume contains peculiar geobodies, growing precisely from perforation holes spaced at a 40 ft interval in a treatment well landed in the Middle Bakken. These geobodies penetrate through the Lower Bakken Shale reservoir and terminate at the top of the Three Forks dolomites. While our interpretation of the extracted geobodies as hydraulic fractures remains an interpretation, the remarkably high resolution of seismic images obtained in both case studies is unquestionable.