Production History of the Geysers Steam Field

A rather comprehensive reservoir engineering study made by Ramey (1968) of the Big Geysers area contains a table of yearly production, cumulative production, and average pressure of wells producing from the shallow zone in the Big Geysers area for the period from 1957 to 1967. Production prior to 1957 is not included in the cummulative production because of incomplete records. He used the information to plot a p/z curve versus cumulative production to obtain an ultimate steam recovery of 135 billion pounds from the shallow zone to an abandonment pressure of 65 psig. A brief engineering study was presented by Lipman, et al (1977), at which time eleven power generating plants were in operation. Included in that study is a brief picture of the regional drainage system around the Sulphur Bank, Happy Jack, and Big Geysers area showing the shallow reservoir anomaly in relation to the larger regional fracture system. Also presented is a pressure map showing the change of the 500 psia isobar with time and an isobaric map as of April 1977. These two maps cover the area from which wells produced steam into Units 1 to 11. These authors, however, did not present production data to correlate with the pressure behavior that they described. This paper presents a brief history of the development of the field, followed by several examples of production decline curves for wells having six or more years of history. The wells selected have varying production rates and original well spacings. The paper concludes with a section on the monthly, yearly, and cumulative production data as reported to the California Division of Oil and Gas