Reservoir Dynamics Monitoring in A Liquid Dominated Geothermal Field Based on Surveillance Data and Tracer Flow Test

Abstract

Two common characteristics changes in the liquid-dominated reservoir because of exploitation are a decrease in temperature in the liquid reservoir zone (due to injection breakthrough) and the development of a steam zone (because of lower liquid water level). Both phenomena are observed by using the tracer flow test (TFT) technique. The comprehensive analysis using enthalpy from TFT data, combined with the data of chloride in brine, NCG in steam, and subsurface temperature (from PT logging), can be used to identify the dynamics of the reservoir processes. The application of the comprehensive analysis is selected for this study by taking those various monitoring of surveillance programs from a liquid-dominated geothermal system. In the selected geothermal field, which the operation began in 1994, an injection breakthrough occurred in the western part of the field. On the other side, the development of a steam reservoir was observed in the eastern part of the field. TFT monitoring is carried out every three months in each active production well as stated in the surveillance program. Other chemical monitoring and (PT) log data are also carried out periodically. Two wells from the studied field are selected, in which one well experience with injection breakthrough and the other one is in steam cap development. Comprehensive analysis results from TFT data, geochemical monitoring data (NCG and Cl), and subsurface temperature are used to understand the dynamics in geothermal reservoirs. Injection breakthrough in production well is indicated by changes in chloride content, decrease in enthalpy and NCG in the steam. Whereas the formation of steam cap will be characterized by an increase in enthalpy and NCG. With a thorough understanding of the changing conditions in the reservoir, recommendations for appropriate surveillance strategies can be formulated to maintain an optimal and sustainable generation process.