Petrologic Indicators of Permeable Structures in the Botong Sector of the Bacman Geothermal Production Field

Abstract

Well permeability and productivity in most geothermal wells are attributed to geologic structures. The diagnosis of structural permeability in the subsurface is thus critical in geothermal exploration and development. Petrologic data is used in the preliminary evaluation of structural permeability during drilling. The petrologic parameters currently used in identifying structures are I) mylonites, 2) veins, and 3) increase in alteration intensity. The study which focuses on the Botong sector of the Bacman geothermal production field aims to assess the applicability of these petrologic parameters and to establish a set of petrologic criteria for structural permeability. OP4D. the most permeable of the five Botong wells, is characterized by generally moderate amounts of drusy veins, and moderately to intensely altered rocks. In contrast, OP-3D, which has relatively poor permeability, has weak veins and veinlets and moderately altered rock. It has also prehnite veins. Mylonites appear as an inconclusive permeability indicator.