Interwell tracing by environmental isotopes at Fimkassar Oilfield, Pakistan

Water flooding is an important operation to enhance oil recovery. Movement of injected water is traced to test the performance of the water flood and verify suspected geological barriers or flow channels, etc. This paper describes the application of environmental isotopes as interwell tracers at Fimkassar Oilfield in Chakwal District, Pakistan. Water flooding was started in March 1996 in the Sakessar formation (Eocene). When water appeared in the production well in June 1998, isotopes (18O, 2H and 3H) were used to determine the breakthrough/transit time of the water flood and the contribution of fresh injected water. Water samples were collected during June 1998-August 1999 from the injection well, the production well, and some other fields for reference indices of the Sakessar formation and analyzed for the 18O, 2H and 3H, and chloride contents. The isotopic results confirmed the breakthrough of injected water and indicated that the water in the production well was a mixture of the injected water and the formation water. The initial breakthrough time was 27 months. The contribution of injected water varied from 67% to 80%. This percentage did not change significantly from the time of breakthrough until the last sampling indicating good mixing in the reservoir and the absence of any high permeability channel. Chloride content did not give any information about the hydraulic connection between the injection well and the production well. The study proved the potential of environmental isotopes for interwell tracing.