The Subsurface and Drilling Aspects of The Successful 2020-2021 Make-Up Well Drilling In Wayang Windu Geothermal Field, Indonesia

Star Energy Geothermal completed the make-up well drilling campaign in 2020-2021 to maintain steam supply for the existing 227 MWe power generation in Wayang Windu geothermal field. As a primary objective, based on the steam supply profile, 6 (six) production wells were required to be drilled in this campaign, three wells producing from the steam reservoir and three wells producing from the deep brine reservoir. This combination was necessary to maintain field pressure decline by balancing steam and liquid reservoirs production. Wells prepared in this campaign consist of one re-drill well, four new wells drilled from the existing pad, and one well from the new well pad. Based on historical data, drilling deep into the brine reservoir has been particularly challenging in Wayang Windu field. Several initiatives have been implemented to achieve the objective of this campaign, including lessons learned from previous drilling campaigns as part of continuous improvement. The initiatives in the subsurface area include refining well targeting assessment and detailing potential geological hazard identification, especially in the deep reservoir section. While in the drilling area, several initiatives were made, such as better well planning and improvement in drilling practice. As a result, the drilling campaign was completed with significant success: steam output above the target, successful drilling to the deep brine reservoir, and finishing the campaign with a faster and lower cost than the plan. Moreover, the success of this campaign in drilling deep brine wells has provided more information for the resource team to characterize better the deep brine reservoir for resource assessment/reserves estimation to enable future field development of the Wayang Windu geothermal field.