Horseshoe-Gallup Water Injection Project-An Engineering Challenge

Abstract

Abstract The Horseshoe-Gallup unit, which comprises about 75 per cent of the Horseshoe-Gallup field, is located near the northwest corner of New Mexico. A pressure maintenance project utilizing water injection is now in operation in the unit. The reservoir is similar to the many other Gallup sand developments in the area, most of which are thin, elongated stratigraphic traps which produce by solution gas expansion. Several of the Gallup reservoirs are being flooded at this time, however little is known by The industry of the problems involved in these floods. The paper discusses the reservoir properties, history and problems encountered in the operation of the Horseshoe- Gallup unit pressure maintenance project. The difficulties encountered in this project are probably typical of what can be expected in most Gallup reservoirs. Although these problems could result in reduced recoveries and increased investments in comparison to conventional water injection programs, a prior understanding of the reservoir will minimize the effects and permit reasonable estimates of performance. Introduction The Gallup sand is the most prevalent oil producing horizon in the Four Corners area of New Mexico. There are 20 fields in this area which produce from the Gallup sand. These fields contain about 1,300 active wells and have produced a cumulative 67 million bbl of oil. The Gallup reservoirs are solution gas driven with rather modest primary recoveries in the order of 10 to 15 per cent. A rapid decline in producing rate, coupled with the low primary recovery, makes these reservoirs excellent candidates for pressure maintenance by water injection. At this time, there are 12 water injection programs underway in the Gallup reservoirs. Very little information has been published on these projects or the problems that arise during water injection. Presented in this case history are the problems that were found in one of these projects, the Horseshoe-Gallup unit. This unit covers most of the Horseshoe-Gallup field and is the largest Gallup flood operated as a single project in Northwest New Mexico. It is also the largest water injection project operated by The Atlantic Refining Co. The information gained in Horseshoe-Gallup should be helpful to the operators of other water injection programs in the Gallup sand. Geology and Reservoir Characteristics The Horseshoe-Gallup field is located in San Juan County, N. M., near the northwest corner of the state. Geologically, the field is on the northwest rim of the San Juan basin. Most of the field is actually situated on the Four Corners Platform with only about a fourth of the field located on the steep hogback monocline dipping into the San Juan basin (Fig. 1).Oil production is from a large stratigraphic trap of Cretaceous age about 14 miles long and 3 miles wide which trends in a northwest-southeast direction. The Gallup sand in the Horseshoe field varies in depth from 800 ft in the northwest to 3,400 ft at the southeast end of the field where it dips into the San Juan basin. However, within the Horseshoe-Gallup unit area, the sand is encountered from 800 to 1,600 ft deep. JPT P. 1101ˆ