Strategies for Optimal Enhanced Recovery of Heavy Oil by Thermal Methods, Midway-Sunset Field, Southern San Joaquin Basin, California

A previously idle portion of the Midway-Sunset field, Aera Energy's Pru Fee property, has been brought back into commercial production through tight integration of geologic characterization, geostatistical modeling, reservoir simulation, and petroleum engineering. This property, shut-in over a decade ago as economically marginal using conventional cyclic steaming methods, has a 200–300 foot thick oil column in the Monarch Sand. However, the sand lacks effective steam barriers and has a thick water-saturation zone above the oil-water contact. These factors require an innovative approach to steam flood production design that balances optimal total oil production against economically viable steam-oil ratios and production rates. The methods used in this DOE Class III oil technology demonstration are accessible to most operators in the Midway-Sunset field and could be used to revitalize properties with declining production of heavy oils throughout the region. The production strategy adopted in the steam flood pilot is to restrict steam injection to the upper one-third of the pay zone, that portion where oil saturations exceed 50%. Any steam injected below this interval would loose large quantities of heat to water and result in unfavorable steam-oil and water-oil ratios. During the fourth year of the oil demonstration project, production from the 8 ac four-pattern steam flood pilot continued to remain high. As of December 1999, the oil rate was averaging 308 BOPD and the cummulative oil production from the pilot alone was 335 MBO. The steam-oil and water-oil ratios, measures of steam flood effectiveness, closed the year at about 5 and 8, respectively. Also, an additional 37 new wells drilled in 1998 surrounding the pilot have been put into cyclic production. By the end of 1999 they were producing up to 458.3 BOPD, bringing the total oil rate for the Pru Fee property up to 689.0 BOPD. The total production from the property since the beginning of the project in late 1995 is 541.0 MBO. The average production rates per well are higher under steam flood than in cyclic mode.