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Abstract ARCO Oil and Gas Company has drilled two horizontal drainhole wells in the Empire Abo Unit. A horizontal drainhole well is one in which the wellbore is turned from vertical to horizontal in a short radius and the horizontal hole is then drilled out some distance into the formation. These wells were drilled to evaluate the mechanical feasibility of the drilling process and to examine the effect producing through the drainholes would have on the well's tendencies to form gas cones. Although several problems were encountered while drilling the problems were encountered while drilling the drainholes, the drilling technique used does seem to be mechanically sound. The wells have not been on production long enough to fully evaluate their gas coning performance as compared to conventionally performance as compared to conventionally completed wells. This paper will briefly examine the gas coning problem in the Empire Abo Unit, discuss some of the techniques used to limit gas coning in the Unit, and review ARCO's experience with horizontal drainholes. Introduction ARCO Oil and Gas Company operates the Empire Abo Unit, located in the Empire Abo Pool of Eddy County, New Mexico (Figure 1). The Unit consists of approximately 11,000 acres and represents about 97% of the entire pool. Production is from the Permian (Lower Leonard) Abo Reef dolomite at a depth of approximately 6200'. The productive reef development is productive reef development is approximately 12.5 miles long and 1.5 miles wide (Figure 2). The cross-sectional view in Figure 3 illustrates the massive reef development. The main producing mechanism is gravity drainage which is now supplemented by the injection of the residue gas into the gas cap. The pool was discovered in 1957. Competitive development of the field on 40-acre spacing was rapid. The pool was operated on a competitive basis until 1973 at which time the Empire Abo Unit was formed. S.H. Christianson's paper gives a detailed description of the reservoir and discusses factors involved in the formation of the Unit. Prior to unitization, approximately 96 MMBO were produced from the Abo Reef. An additional 91 MMBO have been produced from the date of unitization through April, 1980. The Unit's current production rate is about 25,000 BOPD. production rate is about 25,000 BOPD. GAS CONING IN THE UNIT At the time of discovery, the Abo reservoir pressure was above the crude's bubble point. Competitive production of the pool resulted in a drop in pressure to below the bubble point and the formation of a secondary gas cap. By the early 1970's several wells in the up-dip area of the pool began to produce at gas/oil ratios (GOR's) in excess of the solution GOR indicating the production of free gas from the gas cap. Drill stem test information indicated that these high GOR wells were perforated below the level of the regional perforated below the level of the regional gas/oil contact. Localized depressions in the gas/oil contact around the wellbores (gas cones) were causing the high GOR production. production. Producing Empire Abo wells at high GOR's is undesirable for two reasons. |
