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Empire Abo field
The Empire Abo field, located in New Mexico, US, covers ≈11,000 acres (12.5 miles long by 1.5 miles wide) and contains approximately 380 million stock tank barrels (STB) of original oil in place (OOIP).[1][2] This reservoir is a dolomitized reef structure (Fig. 1) with a dip angle of 10 to 20° from the crest toward the fore reef. The oil column is approximately 900 ft thick, but the average net pay is only 151 ft thick. The pore system of this reservoir is a network of vugs, fractures, and fissures because the primary pore system has been so altered by dolomitization; the average log-calculated porosity was 6.4% BV. Numerical simulations of field performance and routine core analysis data have indicated that the horizontal and vertical permeabilities are about equal. The Empire Abo field had a small initial gas cap (< 1% of the hydrocarbon PV), so the oil was gas saturated at the original reservoir pressure of 2,360 psia. The oil gravity was 43°API, and viscosity at reservoir conditions was approximately 0.4 cp.
![Fig. 1 - Empire Abo field. Typical back-reef to fore-reef cross section with opehnole gamma ray/neutron logs.[1]](/w/images/thumb/e/e6/Vol5_Page_1138_Image_0001.png/300px-Vol5_Page_1138_Image_0001.png)
Fig. 1 - Empire Abo field. Typical back-reef to fore-reef cross section with opehnole gamma ray/neutron logs.[1]
![Fig. 1 - Empire Abo field. Typical back-reef to fore-reef cross section with opehnole gamma ray/neutron logs.[1]](/File:Vol5_Page_1138_Image_0001.png)
Gas injection
The field was discovered in 1957 and unitized in 1973. At that time, high gas/oil ratio (GOR) back-reef wells were shut in, only the downdip solution-GOR wells continued to produce, and gas-plant residue gas was reinjected into some of the former crestal production wells. The unit added 56 infill producers on 20-acre well spacing in the downdip area during the mid-1970s (see structure map in Fig. 2). In the late 1970s, 100 additional producers on 10-acre well spacing in the downdip area were drilled.
![Fig. 2 – Empire Abo field. Structure map on the base of the Abo reef.[1]](/w/images/thumb/1/18/Vol5_Page_1138_Image_0002.png/300px-Vol5_Page_1138_Image_0002.png)
Fig. 2 – Empire Abo field. Structure map on the base of the Abo reef.[1]
![Fig. 2 – Empire Abo field. Structure map on the base of the Abo reef.[1]](/File:Vol5_Page_1138_Image_0002.png)
Ultimate recovery
Because of the concentration of producing wells downdip, the gas cap draped downdip along the top of the reservoir. The Empire Abo field overall performance was excellent because of its very high vertical permeability; however, gas coning was a major issue, with the overall relatively low reservoir permeability of approximately 50 md. In 1979, Empire Abo was the site of one of the first applications of horizontal wellbores to minimize gas coning.[3] The field is currently being blown down to recover as much gas as possible. On the basis of production data through 2002, on a stock-tank-oil basis, approximately 74% of the OOIP has been recovered from this field by application of the immiscible gas/oil gravity drainage process.
References
- ↑ 1.0 1.1 1.2 Christianson, S.H. 1977. Performance and Unitization of the Empire Abo Pool. Presented at the SPE Permian Basin Oil and Gas Recovery Conference, Midland, Texas, 10-11 March 1977. SPE-6384-MS. http://dx.doi.org/10.2118/6384-MS
- ↑ Killough, J.E. and Foster Jr., H.P. 1979. Reservoir Simulation of the Empire Abo Field: The Use of Pseudos in a Multilayered System. SPE Journal 19 (5): 279-288. SPE-7418-PA. http://dx.doi.org/10.2118/7418-PA
- ↑ Stramp, R.L. 1980. The Use of Horizontal Drainholes in the Empire Abo Unit. Presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, 21-24 September 1980. SPE-9221-MS. http://dx.doi.org/10.2118/9221-MS
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See also
Immiscible gas injection in oil reservoirs