| Abstract |
The two main costs of geothermal development projects are drilling and power plant construction. Mixed fleet drilling offers a proven method to significantly reduce a project’s drilling costs by making use of less expensive ‘top-holing’ rigs for the upper sections of wells, typically down to the production casing depth. A standard 2,000 hp ‘big-rig’ can then complete the well. Taking an example from a production drilling campaign in Kenya using Cluff Geothermal’s 1,000 hp Epiroc Predator rig, it is shown that the mixed fleet approach can also be adopted in the exploration drilling phase, where expensive drilling related risks are prevalent owing to poorly understood subsurface conditions. In volcanic settings, the top section typically presents the most challenging drilling conditions. Using a small, inexpensive drilling rig for this section can save developers significant sums of equity capital, even when factoring in the cost of mobilising both a top-holing rig and a big-rig to a project, as challenging downhole conditions can result in delays to the drilling process and downtime. The deep geothermal drilling industry is motivated to provide developers with high cost big-rigs as this results in greater returns for their shareholders. The mixed fleet drilling approach is cost comparative to a ’budget’ big-rig drilling operator across a campaign of three or more wells. There should be a step change within the global geothermal sector to deploy mixed fleet drilling as a standard means of de-risking drilling operations. |