Abstract

Lower completion costs and enhanced production economics in the Hubbard/Una Mas (Cherry Canyon) field, Loving County, Texas, result from integration of reservoir description, particularly the pore-lining mineralogy, with completion planning for the upper Cherry Canyon Formation U-2 sandstone (Permian, middle Delaware Group). Qualitative thin-section petrography, scanning-electron microscopy, and x-ray diffraction analyses document the reservoir mineralogy and rock-fabric elements and impacted completion procedures in the U-2 reservoir from 1986-1988. The Cherry Canyon reservoir sandstones are gray to light-olive gray, fine to very finegrained, calcareous to argillaceous, lithic and subfeldspathic to feldspathic sandstone and coarse siltstone, interbedded with thin laminae of dark gray siltstones and shales. Detrital illite with diagenetic pore-lining illite, chlorite, and mixed-layered chlorite/smectite clays are present. Micritic calcite cements and euhedral ferroan calcite often reduce effective pore-throat diameters. These clays and cements have significant potential to reduce reservoir deliverability. Pore-lining, acid and salinity-sensitive clays require controls on water loss and utilization of 2% KC1 in all completion and stimulation fluids to prevent deflocculation of detrital clays or swelling of authigenic mixed-layered clays. Taking the U-2 reservoir mineralogy into account, the scale of Cherry Canyon acid fracture-stimulation procedures is reduced. Minimal quantities of formulated acid to clean up the perforations and smaller-scale fracture programs emerge as the optimal completion procedure. This synergy significantly reduces completion costs, results in higher initial oil production for accelerated payout, provides 30% higher cumulative production, and stabilizes the oil-to-water production over a documented five-year production history.