Economic Potential and Optimum Steamflood Strategies for Trough Reservoirs of San Joaquin Valley, California

K. C. Hong and David J. Use

Many heavy oil reservoirs lie along synclinal axes in the Western San Joaquin Valley, California, where thermal EOR activities have been steadily increasing since the early 1960s. While many of these reservoirs have been economically exploited by steam injection processes, others remain undeveloped because reserve bases are smaller and lie in areas where development activities have been historically low. This paper presents a simulation study conducted to develop guidelines for selecting economically exploitable trough reservoirs and optimum steamflood strategies for exploiting them.

Reservoir models representing different reservoir configurations and reserve bases were used to predict oil production performance of trough reservoirs under different operating scenarios. Such economic yardsticks as net oil production, cumulative steam-oil ratio at the economic limit, and profit/investment ratio were used to compare the economic potential of different reserve bases. The results then were used to develop guidelines for selecting reservoirs that can be economically produced. Operating strategies, studied to determine the optimum development strategy for the selected reserves, included injection/production well locations, steam injection conditions, and rate reduction schedules.

The study showed that, for a trough reservoir to be an economical prospect, it should contain a minimum oil in place of 300,000 bbls per pattern length along the trough between the two anticlinal axes. Optimum steamflood strategy for such reservoirs includes: (1) placing the injector(s) away from the synclinal axis and gas-oil contacts, (2) having a row of producers updip from the injector and another near the synclinal axis, (3) starting the steamflood with an intermediate rate and high quality of steam, and (4) shutting in steam injection after 5.5 years of continuous injection at a constant rate. This strategy can result in a annual rate of return of 20%.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California