Reducing Gas Production Decline Through Dewatering: A Case History From the Naturally Fractured Aguarague Field, Salta, Argentina

Abstract

Abstract The Aguarague field is located in the Devonian Basin, NW of the Province of Salta, Argentina. Gas production is obtained from clastics of the Huamampampa formation through an intense network of natural macro and microfractures. The reservoir is in a North-South trending symmetrical anticline. Five high-deliverability gas wells watered-out between 1991 and 1994 and as a result the field gas production decreased substantially. This triggered a study in 1995 to try to find a means of enlarging the life of the reservoir. The study indicated that without any modifications gas production could be expected to lapse at most to 1999. This paper describes how a detailed fracture characterization led to a dewatering project using gas lift, which significantly reduced the gas decline of the reservoir. The project also brought back to gas production some of the wells that had previously watered-out. The 1995 forecast is compared with the actual production performance to date. Introduction Argentina deep drilling (about 4500m) and discovery of hydrocarbons in NOA Basin, Serranias de Aguarague, Baja de Oran, and Ipaguazu, and in the Devonic and Carbonic sub-basins started in 1951 with the discovery of Campo Duran, a gas condensate reservoir, in the Serrania de Ipaguazu. Madrejones field, north of Campo Duran, was discovered in 1952. The field also produced gas and condensate. A shallower well was drilled in Pena Colorada in 1968. The well produced small oil quantities from the top of the Los Monos formation. Ramos field was discovered in the Serrania de San Antonio in 1977. The field produced gas and condensate from the Huamampampa formation. The Aguarague field, object of this study, was discovered in 1979 with the drilling of well Cu.x-1. The field went on production in 1979 with well Cu.x-2, which produced initially at about 500,000 m3/day from the Huamampampa formation. To date, 16 wells have been drilled, out of which 13 reached the Huamampampa formation. The field reached a production of over 4 million m3/day in 1985. However, five high-deliverability gas wells watered-out between 1991 and 1994 and as a result the field gas production decreased substantially. Figure 1 shows a structural map on top of the Huamampampa formation. Water was advancing from the north in such a way that wells Cu.x-2 and Cu.x1 had watered out by May 1991, well Cu.x-3 by May 1993, well Alo.x-1 by June 1994 and well Sa.Ag.-4 by January 1995. Water was also advancing from the south and well Tr.x-1 watered out in January 1986, well Tr.x-206 in August 1991 and well Tr.x-199 in September 1992. Without any modifications all the wells were going to water out by 1995. Location and Geology The Sierra de Aguarague field is located in the Devonian Basin, NW of the Province of Salta (Figure 2), west of National Route No. 34 near the city of Tartagal.