A Successful Peripheral Water Injection in a Weak-Edge Aquifer Oilfield, Oriente Basin, Ecuador

Abstract

Abstract HN oilfield1, Oriente Basin, Ecuador, is located in the rain forest, well deployment is restricted by ground environment, and surface facility installation is under very strict regulations2. In this paper, a successful peripheral waterflooding3 application in the HN oilfield, was illustrated. Geological study, waterflooding design, project deployment and waterflooding optimization were thoroughly discussed in detail. M1 of Mesozoic Cretaceous Napo Formation is a litho-structural composite reservoir, mid-high permeability, with thin sand layers4. The production was initialized in 1995 with natural depletion drive, and a 6.4% recovery of OOIP was achieved. In order to enlarge the waterflooding sweep volume, three injection wells were designed. Well location is optimized on the basis of fine interpretation of low relief structure and prediction of sand with average thickness of 15 ft by MPS method5. A proper injection-production ratio(IPR) was determined by using reservoir simulation to restore the reservoir energy but avoiding to reach high water-cut values on producer wells. Volume and properties of the aquifer was estimated by static-dynamic analysis. A "balanced injection" method was applied and real-time waterflooding adjustment was carried out to enhance waterflooding performances. As liquid production and pressure declined sharply after 8 years' primary drive, in 2003, one injection well was drilled to performance peripheral water injection. The volume and properties of the aquifer were re-estimated according to the production history data and geological analysis. Oil production started to increase and reservoir pressure was restored. The BOPD in 2003 was 950bbl/d, and peaked at 2,300bbl/d in 2007. Later, another two injection wells were drilled to enlarge the sweep volume. But one of them was changed to inject in another zone. Injection volume, pressure, and injection mode were studied and optimized, the oil production peaked at 5,400bbl/d in 2010 as the results of injection optimization. The efforts of real-time waterflooding adjustment extended the high oil production period. By July 2015, RF reached 32.7% with 83.4% water-cut and an ultimate recovery was forecasted to be 45%. Due to effective reservoir management, maximized economic benefit was achieved on the basic economic evaluation. Suggestions on future adjustments were given for waterflooding operations in this field and similar oilfields. The successful application of waterflooding demonstrated the potential of peripheral water injection in complex reservoirs and the importance of water flooding design. Due to integrated geological study, reservoir performance analysis, and reservoir management, waterflooding operations achieved its best performance with maximum economic benefits.