Design and Implementation of a CO2 Flood Utilizing Advanced Reservoir Characterization and Horizontal Injection Wells In a Shallow Shelf Carbonate Approaching Waterflood Depletion, Class II

Abstract

The purpose of this project was to economically design an optimum carbon dioxide (CQ) flood for a mature waterflood nearing its economic abandonment. The original project utilized advanced reservoir characterization and C 0 2 horizontal injection wells as the primary methods to redevelop the South Cowden Unit (SCU). The development plans; project implementation and reservoir management techniques were to be transferred to the public domain to assist in preventing premature abandonment of similar fields. The Unit was a mature waterflood with water cut exceeding 95%. Oil must be mobilized through the use of a miscible or near-miscible fluid to recover significant additional reserves. Also, because the unit was relatively small, it did not have the benefit of economies of scale inherent in normal larger scale projects. Thus, new and innovative methods were required to reduce investment and operating costs. Two primary methods used to accomplish improved economics were use of reservoir characterization to restrict the flood to the higher quality rock in the unit and use of horizontal injection wells to cut investment and operating costs. The project consisted of two budget phases. Budget Phase I started in June 1994 and ended late June 1996. In this phase Reservoir Analysis, Characterization Tasks and Advanced Technology Definition Tasks were completed. Completion enabled the project to be designed, evaluated, and an Authority for Expenditure (AFE) for project implementation submitted to working interest owners for approval. Budget Phase I1 consisted of the implementation and execution of the project in the field. Phase I1 was completed in July 2001. Performance monitoring, during Phase 11, by mid 1998 identified the majority of producing wells which under performed their anticipated withdrawal rates. Newly drilled and reactivated wells had lower offfake rates than originally forecasted. As a result of poor offfake, higher reservoir pressure was a concern for the project as it limited C02 injectivity. To reduce voidage balance, and reservoir pressure, a disposal well was therefore drilled. Several injection surveys indicated the C02 injection wells had severe conformance issues. After close monitoring of the project to the end of 1999, it was evident the project would not recover the anticipated tertiary reserves. The main reasons for under-performance were poor in zone CO2 injection into the upper San Andres layers, poorer offtake rates from newly drilled replacement wells and a higher than required reservoir pressure. After discussion internally within Phillips, externally with the Department of Energy (DOE) and SCU partners, a redevelopment of South Cowden was agreed upon to commence in year 2000. The redevelopment essentially abandoned the original development for Budget Phase I1 in favor of a revised approach. This involved conformance techniques to resolve out of zone CQ injection and use of horizontal wells to improve in zone injectivity and productivity. V Phase 2 activities commenced in October 2000 w i t h ...

Application of Horizontal Waterflooding To Improve Oil Recovery From Old Oil Fields

“…EnCana (formerly PanCanadian) used a combination of vertical and horizontal wells to maximize the performance of a CO 2 flood in the Weyburn Field, Canada 18 . Phillips evaluated horizontal injection wells to accelerate the recovery of oil from the South Cowden Unit and to permit the centralization of field handling facilities 19 . ARCO used a combination of vertical and horizontal wells in the implementation of an enriched gas drive project in Prudhoe Bay 20 .…”