| Title | Use of Deep Slimhole Drilling for Geothermal Exploration |
|---|---|
| Authors | K.M. Mackenzie, G.N.H. Ussher, R.B. Libbey, P.F. Quinlivan, J.U. Dacanay and I. Bogie |
| Year | 2017 |
| Conference | Indonesian Geothermal Association Conference |
| Keywords | geothermal exploration, resource uncertainty, financial risk, conceptual model, deep slimhole drilling |
| Abstract | Deep slimholes were used very effectively in Indonesia in the 1990’s for geothermal resource delineation and potentially again have a major role in assisting early exploration of geothermal prospects that are increasingly challenging because of ambiguous surface indications and more remote and difficult terrain. 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. In the absence of tariffs commensurate with the risks in exploration drilling, developers are cautious to embark on high cost drilling, particularly where the probability of successfully finding a resource with the first few wells may be low because of resource uncertainties. Deep slimhole drilling using equipment that is smaller and requires less road and water supply infrastructure can achieve exploration outcomes at lower cost. However, successful application of this technology requires a solid foundation comprising five elements: an appropriate well design; a simple and clear strategy covering major drilling decision points; a robust procurement and implementation plan; a suitably experienced and equipped drilling contractor; and experienced technical supervision of the operation. Following this approach it is possible to obtain exploration and resource characterisation equal to that provided by full sized exploration wells. The use of deep slimholes can improve the success rate of subsequent appraisal drilling using conventional or large diameter wells and so it can provide cost savings on the total project cost. The use of deep slimholes for exploration reduces the early capital spend on a project, and therefore improves the success-weighted Net Present Value (NPV) of a project, particularly where there is a reduced probability of successfully finding a resource. In combination, the reduced capital and improved scheduling of expenditure plus reduced cost of failure for a project (or for a portfolio of projects), has the ability to reduce the tariff required for geothermal projects in Indonesia. Small diameter wells can potentially produce geothermal fluids sufficient for several hundreds of kW of electricity, raising the possibility of a group of such wells supplying electricity economically in areas where demand is low such as small, remote or isolated grids. The feasibility of doing this in Eastern Indonesia is currently being considered. |