Fracture Characterization at the Dickman Field, KS: Integrating Well Log and Prestack Seismic Analyses



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Dickman Field, located in Ness County, Kansas, has produced 1.7 million barrels of oil since 1962 and is presently being evaluated by the University of Houston as a potential CO2 sequestration locality. The primary injection target is a porous, brine-saturated, Mississippian carbonate unit set approximately -2000 ft (-610 m) subsea. The objective of this study is to characterize sub-vertical fracture networks that potentially favor mobility of free-state CO2 within the reservoir. The 6 Hz results from a narrow-band decomposition of the Dickman 3D broadband volume show NW and NE striking lineaments in the reservoir interval. These spectral anomalies were originally assumed to be evidence of sub-resolution fracturing. Testing the validity of these features was accomplished by analyzing two kinds of data: 1) digital well logs from nearby wells and 2) available prestack seismic data from the Dickman 3D survey. A fuzzy inference system was used to obtain ground-truth fracture information from conventional well logs. Results show probable indicators of crosscutting fractures in the Mississippian section. Prestack analysis was used to detect azimuthal variations in the reflectivity gradient using amplitudes picked from the Gilmore City horizon. Azimuthal anisotropy orientations agree with the 6 Hz features as well as with lineament orientations found in previous seismic attribute studies. The 6 Hz anomalies, although supported by geological and geophysical evidence in terms of orientation, are most-likely products of low-frequency noise found in the upper 0.2 seconds of the Dickman 3D.



CO2 sequestration, Kansas, Fracture behavior, Well logs, Fuzzy logic, Azimuthal AVO, Seismic attributes