Field Consolidation of Fractured Core

Abstract

Abstract A recent investigation of fractured core from the Embar reservoir of the Gebo field, Hot Springs County, Wyo., utilized novel techniques that are believed to be worth reporting. The most successful procedure was to:cut the interval with a rubber sleeve core barrel;cut the core, encased in the rubber sleeve, into approximately 3-ft sections for ease of handling;plug the ends of the sleeve and displace the drilling mud, oil and water from around the core with a polyester resin;allow the resin to polymerize; andslab the core, which is cast in resin, and investigate the amount and type of fracturing exposed. Discussion An in-fill well to be drilled in the Gebo field, Hot Springs County, Wyo., provided an opportunity to do some additional coring in the fractured Embar formation. Since the recovery from this formation had been poor, the Gebo Unit No. 47 was scheduled to core the Embar using a rubber sleeve core barrel. The upper productive member of the Embar formation was cored in two 20-ft sections at an average rate of 15 min/ft, with a core recovery of 95 per cent. When the 20-ft sections of core encased in the rubber sleeve were removed from the core barrel, it was obvious from the limber nature of these sections and a number of narrow necks (or points of reduced diameter of the sleeve) that the core was broken into a number of pieces. In order to study the anticipated fracture system at leisure in the lab, alternate 3-ft sections of the core were cast into plastic briquets at the rig site. Several different plastic application techniques were tested, and the most successful method is described in this note. About 2 in. of core were removed from the end of each 3-ft section to be plastic treated. Rubber stoppers (with flared copper tubing running through them) were clamped in place, and the section was placed in a holder. This holder kept the rubber sleeve from expanding to more than 3 1/2 in. OD and kept fractures from being wedged open and increasing the length of the core. (See Fig. 1.) The section of core in the holder was then mounted vertically, and plastic was pumped into the bottom of the sleeve. (See Fig. 2.) Enough plastic was pumped into the bottom of the section of core to displace most of the oil, mud and water out the top of the core. After about 250 ml of clean plastic had been produced from the overflow at the top of the holder, the upper copper line was sealed off by bending and crimping; enough additional plastic was pumped into the bottom tubing to expand the sleeve against the holder.