Abstract The Jordan (San Andres) reservoir comprises ~400 ft (120 m) of upward-shoaling subtidal to peritidal carbonate strata, which is now thoroughly dolomitized and partly cemented by sulfates. Subtidal facies include dominant pellet packstone/ grainstone, with local bryozoans, algae, and coral bioherms and associated skeletal grainstone flanking beds. The lower part of the subtidal section is characterized by stratigraphically distinct zones in which permeability has been enhanced by a postburial carbonate-leaching event. These diagenetically altered (leached) zones crosscut subtidal depositional facies. Peritidal facies are nonporous mudstone and generally non- porous pisolite packstone characterized by abundant sulfate cement. The pisolitic rocks are locally porous and permeable where sulfate cement is either leached or absent from fenestrae. Cumulative production is 68 million stock tank barrels (MMSTB) of 218 MMSTB original oil in place, which is a recovery efficiency of 31%. A total of 47 MMSTB of remaining mobile oil occurs as bypassed oil in the contacted upper part of the reservoir, which has been penetrated by well bores; 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, where low-permeability, diagenetically unaltered subtidal rocks are incompletely swept, and the eastern central part of the field, where heterogeneous permeability in peritidal rocks 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, diagenetically altered subtidal rocks are uncontacted, and the central part of the field, where high-permeability, diagenetically altered subtidal rocks are uncontacted. An understanding of diagenetically controlled reservoir properties can be used to predict the locus of remaining resource and to design recovery strategies.

Abstract: Cathodoluminescence is commonly observed in ancient carbonate rocks, yet relatively few examples of geologically young cathodoluminescent carbonates have been reported. Review of young cathodoluminescent carbonates provides constraints on formation of cathodoluminescence by pre-burial processes and aids in interpreting ancient carbonates. Modem skeletal grains are rarely cathodoluminescent. Cathodoluminescence observed in ancient skeletal grains, although not necessarily indicative of diagenetic alteration, certainly should encourage the petrographer to consider the possibility of replacement or recrystallization. Modem inorganic marine precipitates are generally not cathodoluminescent either, although cathodoluminescent magnesian calcite cements have been reported from both deep-water and shallow-water marine environments. Cathodoluminescence in these examples is apparently the result of formation in low-Eh porewaters in which divalent manganese is available. However, these conditions are not necessarily reflected in the trace cation and stable carbon isotope composition of the cements. Pleistocene cathodoluminescent carbonates have been reported from bank-margin settings where these sediments underwent subaerial exposure during glacio-eustatic sea-level lowstands. Meteoric diagenesis during subaerial exposure does not always result in a cathodoluminescent product, however. For example, the post-Miocene coral cap of Enewetak Atoll lacks cathodoluminescence despite ample textural and geochemical evidence of subaerial exposure and recrystallization in meteoric water.

Abstract The Penwell, Jordan, Waddell, Dune, McElroy (P.J.W.D.M.) Field Complex of Ector, Crane, and Upton Counties, Texas, is a single giant oil field which, because of separate initial field discoveries, is divided into five fields. Production is from Guadalupian San Andres and Grayburg carbonate reservoirs. The original oil in place in this giant field complex is calculated to be 4,100 million barrels, cumulative production is more than 800 million barrels, and 900 million barrels of mobile oil will remain after conventional primary and secondary recovery. The P.J.W.D.M. Field Complex is located on the Central Basin Platform in the Permian Basin of West Texas and Southeast New Mexico. San Andres and Grayburg sediments were deposited as an upward-shoaling sequence of low-energy ramp sediments. The lower, marine portions of both formations contain pellet and skeletal grainstone and skeletal wackestone with normal marine fauna. The upper, peritidal portions of both formations contain mudstone and pisolite packstone/grainstone characterized by desiccation features and sulfate cements. The section has been thoroughly dolomitized and contains anhydrite partially hydrated to gypsum. The trap is a low, broad anticline formed by compaction deformation over a buried Pennsylvanian fault system. The reservoir zones are primarily dolomitized subtidal grainstones, and the seals are fine-grained supratidal and peritidal dolomite plugged with sulfate cements. Linear grainstone trends impart lateral heterogenity to these reservoirs, and because they contain a concentration of remaining mobile oil, these features are targets for infill drilling.