| Abstract |
The cost of drilling geothermal wells is estimated to be about 40% of the total investment cost for a new high temperature geothermal plant (Thorhallsson and Sveinbjornsson, 2012). This makes geothermal plants more expensive to build than the conventional fuel fired power plants, and as a result the cost of the wells becomes a key consideration when determining the economic viability of a geothermal field. Accurate costing of geothermal wells is therefore very important as it quantifies a substantial percentage of the cost of the geothermal project. This will help in future planning and budgeting of geothermal projects within the region. Accurate well cost records also makes it possible to carry out analysis of drilling-cost-with-depth and evaluate the benefits of selecting different drilling technologies and materials for various geothermal fields and regions and further couple them with the energy-recovery-with-depth for the field. The purpose of this paper is to develop a cost model for costing high temperature geothermal wells that allows the estimation of well costs from a few key input variables such as well depth, number and size of casing intervals, and well trajectory. The model uses two input parameters, the criteria where the well design is established and the price book where all the costs are listed down. The cost model then calculates the drilling materials required to drill each section of the specified well to completion. The cost of these materials is then automatically calculated using the unit cost that is automatically picked from the price book. The summary sheet then gives the total cost of the well. The paper also describes the well cost structure, the factors that affect the cost of the well and items considered when costing a geothermal well. There is surprisingly little published data available on the breakdown of geothermal drilling costs due to the competitive nature of the drilling market and confidentiality clauses. As a result, the data used for the price book for this model are estimated values. The cost model divides the well cost into three major parts; pre-spud, drilling and completion costs. The pre-spud costs includes all the costs prior to spud-in, while the drilling costs are all the costs incurred while making hole. This includes the rig rental cost and the supervision cost. This is where the bulk of the cost is. Finally the completion costs are the costs incurred after achieving total depth to rig release. |