Application of Reservoir Characterization and Advanced Technology to Improve Recovery and Economics in a Lower Quality Shallow Shelf San Andres Reservoir.

Abstract

The Class 2 Project at West Welch was designed to demonstrate the use of advanced technologies to enhance the economics of improved oil recovery (IOR) projects in lower quality Shallow Shelf Carbonate (SSC) reservoirs, resulting in recovery of additional oil that would otherwise be left in the reservoir at project abandonment. Accurate reservoir description is critical to the effective evaluation and efficient design of IOR projects in the heterogeneous SSC reservoirs. Therefore, the majority of Budget Period 1 was devoted to reservoir characterization. Technologies being demonstrated include: l. Advanced petrophysics 2. Three-dimensional (3-D) seismic 3. Cross-well bore tomography 4. Advanced reservoir simulation 5. Carbon dioxide (CO{sub 2}) stimulation treatments 6. Hydraulic fracturing design and monitoring 7. Mobility control agents. West Welch Unit is one of four large waterflood units in the Welch Field in the northwestern portion of Dawson County, Texas. The Welch Field was discovered in the early 1940`s and produces oil under a solution gas drive mechanism from the San Andres formation at approximately 4800 ft. The field has been under waterflood for 30 years and a significant portion has been infill-drilled on 20-ac density. A 1982-86 Pilot C0{sub 2} injection project in the offsetting South Welch Unit yielded positive results. Recent installation of a C0{sub 2} pipeline near the field allowed the phased development of a miscible C0 injection project at the South Welch Unit. The reservoir quality at the West Welch Unit is poorer than other San Andres reservoirs due to its relative position to sea level during deposition. Because of the proximity of a C0{sub 2} source and the C0{sub 2} operating experience that would be available from the South Welch Unit, West Welch Unit is an ideal location for demonstrating methods for enhancing economics of IOR projects in lower quality SSC reservoirs. This Class 2 project concentrates on the efficient design of a miscible C0{sub 2} project based on detailed reservoir characterization from advanced petrophysics, 3- D seismic interpretations and cross wellbore tomography interpretations. During the quarter, the project area was expanded to include an area where the seismic attribute mapping indicated potential for step-out locations. Progress was made on interpreting the crosswell seismic data and the C0{sub 2} performance simulation was further improved. Construction of facilities required for C0{sub 2} injection were completed.