Identification of Producible and Bypassed Pay Oil Zones in the Smackover Formation by Using API Gravity Determined on Core Samples Together with Determination of Recoverable Oil Reserves through Pyrolysis Analysis*
Albert Maende1, Wesley Ingram2, and W. David Weldon1
The HAWK’s pyrolysis instrument’s Petroleum Assessment Method (HAWK–PAM) was used to analyze cores of the Upper Jurassic Smackover Formation in the Little Cedar Creek Field, Conecuh sub-basin, Alabama, USA. The objective was determination of parameters for locating producible and bypassed oil zones.
The Geological Survey of Alabama provided cores from eight wells. Two hundred thirteen core samples obtained from these cores at intervals of 5 to 10 ft, were analyzed using HAWK–PAM which, is a pyrolysis method whereby, through heating for 45 min over a 50 to 650°C range, five carbon number groupings are generated; C4–C5, C6–C10, C11–C19, C20–C36, and C37+. API gravity and maturity are determined too. After the pyrolysis run, measurement of CO and CO2 to a maximum temperature of 750°C is done. Thus total organic carbon (TOC) is also determined. Core samples whose C4–C36 was ≥2 mgHC/g rock were computed for their API gravity and then grouped into perforated and not perforated (bypassed oil).
Perforated and bypassed oil recoverable reserves were computed from the sum of C19 and C20–C23. TOC and ratios of C4–C36/TOC to non- generating organic carbon, C4–C36/C4–C37+, C4–C19/C20–C36 and maturity were similar for producible and bypassed oil zones. Five out of the eight wells are oil producers. API gravity values identified all the perforated zones in four out of these five wells and located bypassed oil zones in one of them. HAWK–PAM identifies and quantifies producible and bypassed oil zones in Smackover Formation in Little Cedar Creek Field and is also applicable to similar microbial carbonate ramp buildups.
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*Adapted from oral presentation given at GeoGulf 2023, Houston, Texas, April 23-25, 2023
1Wildcat Technologies, 218 Higgins St., Humble, Texas 77338
2Texas Subsurface LLC, 10220 Memorial Dr., Houston, TX 77024