The Rangely Weber Sand Unit miscible CO2 project was initiated in Oct. 1986 and results to date have been encouraging. The development plan of the project has evolved to meet challenges that have developed since startup. Operational changes have also been implemented to improve the economic performance of the unit.
History and Background
The Rangely Weber Sand Unit is in Rio Blanco County, CO (Fig. 1). It is the largest field in the Rocky Mountains in daily and cumulative oil production. Weber sandstone production was discovered at Rangely in 1933 by the California Co. Development of the field did not occur until 1944 when World War II oil demand justified it. Initial development, completed in 1949, was on 40-acre spacing. Hydrocarbon gas reinjection for pressure maintenance began in 1950. Oil production peaked at 82,000 BOPD in mid-1956 just before unitization (Fig. 2).
The field was unitized in 1957 and peripheral water injection started in 1958. Hydrocarbon-gas reinjection continued until 1969 when fieldwide waterflood-pattern injection started. In 1962, water injection was initiated above the gas/oil contact to prevent oil migration into the gas cap. Infill drilling on 20-acre spacing began in 1963 and continued in earnest until the mid-1980's. Most areas of the field are being processed on 20-acre spacing. A 10-acre infill-drilling program, started in 1983, was suspended after marginal results. A total of 898 wells have been drilled in the Weber formation. Currently, there are 372 active producers and 300 active injectors, 259 of which are injecting CO2 with the water-alternating-gas (WAG) process.