Application of Reactive Chemistry for Geothermal Wells in Mt. Apo Geothermal Field, Philippines

Abstract

Mt. Apo geothermal production field has been in operations for over 20 years in the Philippines. Sandawa sector is one of the three sectors in the geothermal field wherein the upflow of the geothermal reservoir is located. A considerable amount of decline in steam availability has been observed in the Sandawa sector throughout the years. It is heavily attributed to the decrease in steam flow in the three wells namely, K5, T3, and T4. These three wells are steam dominated; hence, the available fluid chemistry data is limited. Mineral deposition and blockage of silica scales are the major contributors to the steam decline in the Sandawa sector. This study aims to introduce reactive chemistry to numerical flow modeling to assess how the production fluid chemistry of these wells and the observed minerals are correlated. Numerous versions of 1D radial models were set up using AUTOUGH2 and TOUGHREACT to simulate the behavior of each of the wells. The models represent the major feed zone and the calibration attempts to simulate the production history of each well using geochemical and flow modeling. Each well had a specific input data (i.e. mass production history, pressure, temperature, gas saturation, porosity, permeability, chemistry, mineralogy) well-fitted to the individual wells due to their difference in external processes, such as connectivity with surrounding wells and operations conducted to them at different stages of production. The resulting simulated production history and chemical trends had an overall similar result to the historical measured values with the exception of a few aqueous species and minerals. The matching of chemistry trends and mineralogy using a 1D radial model in TOUGHREACT heavily relied on the knowledge of the well’s history, as well as the kinetic parameters and thermodynamic database used for the simulation. The introduction of several scenarios based on the history of the well was important to acquire a good simulation match to the historical chemistry trends of the well. The results of this study will provide insights for the estimation of the evolution of chemistry and mineralogy of the wells throughout their production lifespan in the geothermal field.