Geochemistry Monitoring During Drilling in Wayang Windu Field

Abstract

Drilling campaign started at Northern area of Wayang Windu area and already drilled for 5 wells. Aerated drilling technique has been becoming a common practice in geothermal well drilling to ensure that the rock cutting sample will not be collected in the borehole and reach to the surface as much as possible or push it into the formation as far as possible. It is also a common practice to keep a production well is kept on running while drilling at the same wellpad. The air entrance into wellbore during drilling may impact the gas chemistry content of adjacent production well due to the existence of similar permeability pathway or fault. The result from gas chemistry monitoring will become strong evidence of fault existence that previously interpreted from geological modeling and geomorphological study. Evaluation of gas breakthrough during drilling indicated by the increasing of gas/ steam ratio or total gas content in steam as the effect of steam condensation process in reservoir when water injected. Detail analyses is include the least soluble gases, such as nitrogen, argon, etc. Major indication is showing by significant increase of N2 and Ar as both are the principal atmospheric gases which are dominantly contributed to geothermal fluid by meteoric water recharge or due to aerated drilling. Other changes observed in gas ratio, such as CO2/N2 ratio and CO2/NH3. This geochemistry observation during drilling gives confirmation about well connectivity in Wayang Windu. Some wells were proofed connected by Cibulak, Pangkalan, and Tunggah Lebak fault, and other fault are unknown at the northernmost well.