Summary

The Jordan (San Andres) reservoir is composed of approximately 400 ft of upward-shoaling subtidal to peritidal carbonate strata that are thoroughly dolomitized and partly cemented by sulfate minerals. The reservoir is divided into four flow units on the basis of depositional facies and subsequent diagenetic alteration. Delineation of these flow units is based on the relationship between open-hole wireline log response and rock mineralogy. Cumulative production is 68 MMSTB of 218 MMSTB original oil in place, which is a recovery efficiency of 31 percent. Forty-seven MMSTB of remaining mobile oil occurs as bypassed oil in the contacted upper part of the reservoir, which has been penetrated by well bores, and 12 MMSTB of mobile oil is in the uncontacted lower part, which has not been penetrated by well bores. The most prospective areas for increased production by waterflood profile modification in the contacted part of the reservoir are the southwest corner of the field, in low-permeability Flow Unit B, which is incompletely swept, and the eastern central part of the field, where heterogeneous permeability in Flow Unit D has resulted in an incomplete sweep. The most prospective areas for increased production through well bore deepening into the uncontacted part of the reservoir are the southeast corner of the field, where high-permeability Flow Unit C is uncontacted, and the central part of the field, where high-permeability Flow Unit A is uncontacted. This reservoir contains 113 MMSTB of oil residual to water-flood, and reservoir properties meet preliminary screening criteria for effective carbon dioxide flooding. Thus, this reservoir is a candidate for enhanced oil recovery operations.

Introduction

The Permian Basin of West Texas and southeastern New Mexico is one of the most mature petroleum producing provinces in the world. Estimates of petroleum resources in the Permian Basin suggest that of the 100 billion barrels (Bbbl) of original oil in place in known fields, approximately 70 Bbbl (70 percent) will remain unrecovered following currently implemented production practices. Importantly, few new reservoirs are being discovered and future reserve growth potential will, therefore, come from these known fields. Our estimates indicate that almost half of this unrecovered oil, approximately 30 Bbbl, resides in dolomitized, shallow-shelf carbonate reservoirs, dominantly in the Permian (Guadalupian) San Andres and Grayburg Formations of the Central Basin Platform. San Andres and Grayburg reservoirs are among the most complex in the Permian Basin, resulting in typical ultimate recovery efficiencies of 30 percent or lower. Thus, detailed geologic and engineering studies of these complex, low-recovery-efficiency reservoirs can identify reserve growth potential both from targeted infill drilling, well deepening, and recompletion opportunities that employ conventional technology, and from enhanced oil recovery operations. In a previous publication we reported that both depositionally and diagenetically controlled reservoir heterogeneity affected production patterns in Jordan field, a dolomitized, shallow-shelf carbonate reservoir in West Texas. The purpose of this report is to use that geologic framework to locate and quantitatively estimate remaining oil, thus targeting the potential for reserve growth. Significantly, this is a very mature reservoir with a limited available data set and, as such, provides a model for volumetric analysis of similar mature reservoirs.

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