Integrated Reservoir Management Enhances Recovery in a Mature Field

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 107885, "Integrated Reservoir Management Enhances the Recovery in a Mature Field," by L.E. Perez, SPE, J.G. Gonzalez, V. Gomez, M.E. Lozano, L.E. Sarmiento, SPE, and J.A. Vargas, SPE, Ecopetrol S.A., prepared for the 2007 SPE Latin American and Caribbean Petroleum Engineering Conference, Buenos Aires, 15-18 April. With the increasing demand for hydrocarbons, many companies are focusing their efforts on maximizing recovery from mature fields. The full-length paper describes the implementation and results of an integrated reservoir-management strategy that revitalized a field that previously was considered to be marginal and currently is one of the main assets of the company. Introduction Yarigui-Cantagallo field is in the Middle Magdalena River basin in Colombia, 180 miles northwest of Bogota, below the Magdalena River. The structure is a faulted monocline, with dips varying from 9 to 50°. Structural features have been identified on the basis of pressure, fluid contacts, and production performance because seismic information is sparse. There are five compartments or Blocks, 1 through 5, where Block 5 accounts for 80% of original oil in place (OOIP). Oil production is from Tertiary fluvial stacked channel sands, divided into three reservoirs: B sands, C sands, and Cantagallo sands. The sands are poorly sorted, friable, and interbedded with shales. Oil is 20°API, asphaltenic, and viscous (20 cp at reservoir temperature, 140°F). The main reservoir is Cantagallo sands, with a 600- to 1,000-ft oil column. Drive mechanism in Blocks 1 through 3 is gas expansion; Block 4 has a strong waterdrive; Block 5 has a combination of gravity drainage, partial waterdrive, and expansion of a secondary gas cap. The field was discovered in 1942 and reached the production peak of 20,400 BOPD in 1962. Ecopetrol has operated the field since 1974. The field had been developed in three drilling programs: 1943–1949 (12 wells), 1953–1962 (40 wells), and 1976–1983 (28 wells). As a consequence of the poor results obtained in several wells from the last program, no new wells have been drilled, and the field was classified as a marginal asset. In 1999, production declined to 5,000 BOPD, with a 35% water cut. Identifying Opportunities Several facts indicated a large potential for additional field development and optimization.OOIP in Yangui-Cantagallo field had been estimated at approximately 750 million STB before Ecopetrol operation. In 1999, the cumulative production was 155 million STB, equivalent to a 20.7% recovery factor for the field. Despite the favorable combination of drive mechanisms, the recovery factor was low considering the intensive drilling and exploitation strategy (80 wells).Most of the wells in the field were completed only in Cantagallo sands because the other two reservoirs, more friable, had a history of sand production.Gas produced from some wells high on the structure led to the inferance of a secondary gas cap, and important portions of the field were not drilled to avoid undesirable gas production.