Waesano, Indonesia: Application of Slimhole Drilling at Waesano Within the GEUDP Programme

Abstract

The Geothermal Energy Upstream Development Program (GEUDP) has been initiated in Indonesia as a joint World Bank and Government of Indonesia initiative to de-risk new geothermal developments by funding and implementing the drilling and evaluation of several exploration wells in selected projects. When testing prospect areas with lower estimated "probability of discovery" (POD), minimizing the cost in case of a negative result becomes more important, particularly with the GEUDP program which intends to recover exploration cost back into the drilling fund once projects are successfully adopted for further development. The use of slimhole drilling was an important component of geothermal exploration of several fields in Indonesia in the 1990’s and has been widely used in Japan, the USA and central America and so was considered as an option for Waesano. The capital expenditure required to drill deep geothermal exploration wells to prove any geothermal system can be substantial particularly if a project is remotely located and requires large infrastructure work to facilitate the exploration and resource proving process. Deep slimhole drilling using equipment that is smaller and requires less road and water supply infrastructure can achieve exploration outcomes at lower cost. Our experience of historic slimhole drilling combined with review of global experience indicates that it is possible to obtain exploration and resource characterization equal to that provided by full sized exploration wells. This paper outlines some of the financial, technical and risk management challenges that greenfield exploration drilling faces and why the response has been the application of slimhole drilling at Waesano as the first project in the program. The merits of different types of well size, depth and drilling technology for Waesano are compared in terms of “exploration effectiveness” and cost. Of more general interest, we present the background information we gathered on slimhole drilling to support the selection of this technology for Waesano drilling, and which may be applicable to many projects in Indonesia and elsewhere.