Benefit of a Typical Injection Well at The Geysers Field

Abstract

An Injection Benefit (IB) Model for a typical injection well has been developed for The Geysers Field. The IB Model is a spreadsheet based model which consists of actual and/or proposed injection rate for wells in gallons per minute (gpm) and converts the injection rate to an average megawatt (MW) increase in steam flow and is based on a rate analysis and a material balance for the entire Geysers Field and is a function of time. One aspect of the IB Model is the calculation of Injection Derived Steam (IDS) which is a tank-model and incorporates the water augmentation history of The Geysers Field and future plans for reservoir management. The Geysers Field at the end of 2013 is made up of approximately 448 wells and electrical generation was 890 MW gross and the injection mass replacement ratio has increased to an annual rate of 78%. As the program of augmented injection has brought mass injection into near-parity with mass production, the rate of reservoir pressure decline has been significantly reduced such that steam flow decline is between 1 and 2%. An IB Model was successfully applied to California Division of Oil, Gas and Geothermal (CDOGGR) data for The Geysers Field. Historical flow data between 1987 and 2013 is included in a single model. Based on study results of a tank-model for The Geysers Field, 83% of water injection is boiling and is needed to match production. A 500 gpm injection well brings about a 4 MW benefit over ten-years. Although this paper documents the overall use of a single tank-model for the entire Geysers Field, the tank-model can be subdivided into two or more parts when a model doesn?t give satisfactory results.