A comparison of reservoir gas energy and composition with respect to initial oil production in the San Andres Formation of Shafter Lake Field, Andrews County, Texas
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Date
2018-05-14Author
Smith, Jacob Ross
0000-0003-4227-0714
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The oil-rich, Permian-age San Andres Formation in the Permian Basin of West Texas produces Wolfcampian-age oil from the dolomitic host rock in prolific amounts. The present study focuses on the Shafter Lake field and utilizes gas analysis reports, well parameters, and 24-hour initial production (IP) reports of oil and associated petroleum gases (preferential to methane) to determine if a correlation exists between formation gas and oil production in the San Andres formation. The San Andres formation undergoes a substantial de-watering process before peak oil-production commences, and this study briefly touches on that subject to account for the massive initial water production which far exceeds the IP of oil. Since the horizontal wells have a first and last perforated zone differential of, on average, twenty-eight times the directional wells, the data is normalized by dividing the production by linear feet of perforated zones. With well type accounted for, normalized IP of oil cross-plotted against normalized IP of gas shows a correlation coefficient of 0.906, which is just over a 90% relation between the oil produced and formation gas produced with it. This relationship can be inferred as either higher oil mobility caused by either gas-cut saturation, or an expanding gas-cap drive upon de-pressuring of the reservoir as a result of extensive production.