--> Heterogeneity in the Pennsylvanian SACROC Unit, Scurry County, Texas, by Michael A. Raines; #90029 (2004)

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Heterogeneity in the Pennsylvanian SACROC Unit, Scurry County, Texas

Michael A. Raines
Kinder Morgan CO2 Co., L.P., 500 North Loraine, Suite 1175, Midland, Texas 79701
[email protected]


SACROC Unit covers the majority of the Kelly-Snyder field and a portion of the Dia-mond “M” field of Scurry County, Texas. It is located in the eastern half of the Midland Basin (the eastern sub-basin of the overall Permian Basin of western Texas and southeastern New Mexico). This 2.8 Billion Stock Tank Barrel (Original Oil in Place) Unit produces from the Pennsylvanian-aged Cisco and Canyon Formations on the Horseshoe Atoll. As is the case with many such Pennsylvanian reef complexes, the SACROC Unit exhibits a great deal of vertical relief and laterally complicated geometries. 

This highly heterogeneous reservoir is currently the focus of tertiary (CO2) recovery efforts. Due to the sensitive nature of mechanical, physical, and economic constraints on tertiary recovery operations, it is important to have a good understanding of the reservoir and fluid migration within it. Therefore, even as tertiary flooding efforts continue in one portion of the field, a renewed focus on gaining an understanding of internal complexities continues in the most complicated portion of the field. In order to develop that understanding, Kinder Morgan CO2 Co., L.P. (KMCO2) recently acquired a 4-D (Time Lapse) cross-well seismic data set in the active project area using Core Labs / Tomoseis (now Z-Seis) equipment and processing. KMCO2 is participating with the Bureau of Economic Geology at the University of Texas at Austin and other regional operators to gain a better understanding of internal architecture as seen through wireline log-correlations. Down-hole video has been run in one open-hole completion, and Injector-to-Producer pressure tests have displayed some very interesting (fast) results. 

The root causes of heterogeneity at SACROC are tectonics, icehouse conditions, and post-burial geochemical processes. Tectonics control growth initiation points and stress con-ditions. Sea level fluctuations force architecture by setting carbonate growth in a “keep-up” mode. This develops overly steep sides and associated erosional potential (truncation and gravity deposits), as well as sudden lateral facies variations during initial deposition. Geo-chemical processes further modify the reservoir through karst overprints, dissolution, and precip-itation. Production operations and treatment techniques further modify reservoir response, primarily through reservoir fracturing and localized pressure modification.

The complexity at SACROC Unit is seen on a variety of scales, is the result of a variety of natural and man-assisted processes, and manifests itself in a variety of ways during field operations. Therefore, a variety of techniques and tools must be focused on the problem in order to gain a reasonable expectation of fluid behavior in the reservoir. Reservoir development plans can not be optimized until an adequate understanding of heterogeneity is available.