4D seismic monitoring of the miscible CO2 flood of Hall-Gurney Field, Kansas, U.S.

Abstract

Time-lapse seismic monitoring of enhanced oil recovery (EOR) programs has been described by several authors over the last 15 years. Advances in equalization techniques have allowed legacy data (in some cases 15 years prior to a monitoring survey) to be used as a baseline. Sensitivity of seismic data to subtle changes in pore composition has been notably improved with the development of dozens of new attribute analysis techniques in the last several years. Unique to our application is the use of nonamplitude, noninversion attributes for monitoring the effectiveness of EOR in thin, shallow (less than 1000 m) carbonates. Considering the very thin (< 5 m) reservoir interval, this first-time, high-resolution 4D survey needed to be highly repeatable, low-cost, high signal-to-noise, and include several repeat surveys prior to breakthrough. Devel-opment of a highly accurate map of CO2 progression through this field was complicated by difficulties propagating high-frequency signal in this near-surface setting, maintaining uniform fold coverage throughout the optimum offset range, vulnerability of signal to contamination by ground roll and air- coupled wave within the noise cone, weak fluid effects due to high carbonate stiffness, and complexity in porosity distribution. Primary and secondary production phases of the 70-year-old Hall-Gurney Field are nearly done. The Pennsylvan-ian Lansing-Kansas City (L-KC) groups have yielded 90 million bls of the 155 million bls cumulative production in the multipay field. Primary production was begun in 1931 and was followed by extensive waterflooding in the 1950s–60s. Waterfloods reached their economic limits in the 1970s–80s but bypassed oil represents a significant resource for CO2 miscible flooding, a third development phase. Reservoir rock of the Hall-Gurney oil field consists of shallow (about 900 m), thin (3.5-5 m), oomoldic limestone layers in L-KC with largely moldic porosities that decrease downward from around 35% to 12%. This reservoir is …