Field testing results are reported for a new conformance-improvement-treatment (CIT) gel technology, where acrylamide polymers are crosslinked with a chromium(III) [CrIII] crosslinking agent. Results are reported for nine field tests performed in Wyoming's Big Horn Basin during 1985 and 1986. All nine treatments were designed to reduce conformance problems encountered in naturally fractured reservoirs. Seven were injection-well treatments, and two were production-well treatments. All nine field tests were operational and technical successes.

Significant amounts of incremental oil production were obtained following five of the seven injection-well field tests and at both production-well field tests. Peak incremental-oil-production rates resulting from the injection-well gel CITs ranged from 38 to 380 bbl/D [6.0 to 60 m3/d]. The first production-well field test, in a carbonate reservoir, generated 7500 bbl [1190 m3] of incremental oil (beyond 4400 bbl [700 m3] of projected base oil production). The second production-well field test, in a sandstone formation, required a smaller than expected gel volume. The second treatment has generated over 14,000 bbl [2200 m3] of incremental oil and did pay out in five months.

Overall, the economics of the field testing program are encouraging. For the seven field tests which stimulated incremental production, incremental stock-tank oil production through May 1987 was 450,000 bbl [71,500 m3]; and the production wells affected by these seven gel CITs were still producing at a combined incremental-oil-production rate of 780 bbl/D [124 m3/d] above pretreatment decline rates. Cost of the seven field tests (including well workover, gel, and gel injection costs) totaled $438,000, yielding a cost for incremental stock-tank oil production through May 1987 of .97/bbl [$6.10/m3].

The field testing program has shown that the new gel CIT technology can generate significant amounts of incremental oil production profitably, even during times of depressed oil prices, and can be used to significantly reduce water/oil ratios (WORs). Field testing has also shown that the gel technology is operationally attractive. At all nine field tests, quality CrIII gel was made consistently and injected without encountering any significant operational, safety, or environmental problems. Little, or no, chromium was detected in associated produced fluids. As intended, significant reductions in injectivity occurred during all the injection-well field tests. The field tests demonstrated that large volumes of gel can be injected into the cited fractured Big Horn Basin reservoirs.

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