Calibration of Surface Seismic Attributes and Impedance Inversions to Natural Fractures Using Horizontal Image Logs — Mississippian Lime, Osage County, Oklahoma
The Mississippi Lime, located in parts of Oklahoma, Kansas, Arkansas and Missouri is one of the most recent unconventional plays, and is characterized by tight limestone, fractured chert, and high porosity tripolitic chert sweet spots. Exploited since the early 1920s, this formation has been rejuventated by the advent of horizontal drilling, hydraulic fracturing, and efficient water disposal into the deeper karsted Arbuckle Formation. In the absence of wide azimuth seismic data, the present-day orientation of maximum horizontal stress can be determined from image logs.
Fracture density is controlled by three factors: strain, lithology, and bed thickness. We estimate strain using volumetric curvature computed from prestack time-migrated surface seismic data. We estimate lithology using lambda-rho mu-rho inversion of the prestack migrated gathers. Finally, we estimate thickness by combining the top and base Mississippian picks and spectral component volumes with the well control. Only a limited number of publications have been reported on the use of image logs measured in horizontal wells. We characterize the fractures seen in these horizontal wells by whether they are layer bound or through-going, open or closed, and by their orientation. These measurements are then correlated to the surface seismic attribute and impedance volumes to estimate fracture density and lithology at the Mississippian Lime objective throughout the survey. Core measurements of the tight and tripolitic chert are used in our lithology estimation. Correlating production from horizontal wells to surface seismic attributes and impedance is problematic and requires a hypothesis that completion is constant along the length of the well. As this play develops into a true resource play, we anticipate the correlation of production data to seismic attributes.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California