Shushufindi is the largest field in the Oriente Basin of Ecuador that was discovered by Texaco in 1970. It has produced about one billion barrels of oil over a period of 30 years. Early in the life of the field, peripheral water injection was implemented and was discontinued in 1999 based on the results of a previous reservoir simulation study carried out in late 90's. Currently, the field is producing significant amount of water under very active water drive mechanism. The field consists of three main stacked reservoirs: Basal Tena, U and T and have produced from about 185 completions. This paper is focused on the reservoirs U and T. Historically, most of the wells in the field were produced commingled from these two reservoirs. . This paper presents the results of an integrated reservoir study that was performed to optimize the field performance for effective reservoir management. A 3D reservoir simulation model was constructed to optimize the performance of the field and to find opportunities to increase oil production. A successful history match achieved helped understanding the reservoir behavior and field performance. Since many wells produced commingled from the reservoirs U and T, dynamic fluid allocation was also performed by means of full-field history matching process. Distribution and location of remaining oil after accounting for the incremental oil recovery due to the workover wells helped delineating the locations of infill and step-out wells to increase production. The results showed that reservoir pressure behavior was very erratic in both U and T reservoirs. However, the level of scatter was more pronounced in Reservoir U than in Reservoir T. Observed reservoir pressure trends seem to follow the channels observed from 2D seismic especially in reservoir U. However, local changes in the pressure trends could have been caused by the water injection. Some observations from the reservoir performance evaluation suggest that the erratic pressure behavior could also be attributed to the change in the formation compressibility due to fluid withdrawal and water injection. The results also show that the effect of peripheral water injection was very limited and infill water injection could improve sweep efficiency of the reservoirs. Introduction The Shushufindi field is located in the Oriente Basin of Ecuador, approximately 100 miles east of Quito as shown in Figure 1. The discovery well was spudded on December 4, 1968 reaching a final depth of 9772 feet, 156 feet within the Chapiza formation (non-economic basement). In early 1969, the exploratory well was completed in the U reservoir (U) and T reservoir (T) of the Napo Formation. The exploratory well Aguarico-1 in the north was completed in April 1969 in the U sandstone. The development-drilling program was initiated in February 1972 with a nominal well spacing of 50 acres. Official production started in August 1972. The main targets were the productive reservoirs in the field, which are T and U sands. In the initial development phase, Original Oil in Place was estimated at approximately 3,500 million barrels of oil. The original reserves of the field were estimated at 1,589 million barrels of oil. By September 2002, the field has produced an estimated 1,013 million barrels of oil. Consequently, the remaining reserves as estimated before this study are approximately 576 million barrels of oil. Initial reservoir pressures were 3,867 and 4042 psia for U and T respectively. By the end of 2002, pressures were 1800 psia for U, and 2500 psia for T. Based on saturation pressures of 1065 and 1265 psia for U and T respectively, and the observed decline rates, the reservoirs are considered under saturated with active water drive. In December 1984, a secondary recovery project was implemented through water injection in order to maintain the pressure and to increase the ultimate oil recovery. In 1999, water injection was suspended and has remained suspended to date. The daily average production in 2002 was 61,000 BOPD with 55% BSW from 61 wells. All the wells are producing under artificial lift mechanisms. The operatorship of this field was transferred to Petroproducción in the 1992 after 20 years of development and production. The last simulation model of the Shushufindi field was built in 1996 with 115 wells.
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