Application for Slim-Wells in Geothermal Exploration and Production

Abstract

Over the last few decades, geothermal development has repeatedly been hampered due to lack of funding when it comes to drilling exploration wells in green geothermal fields. Financial institutions and banks find the risk, involved in the first stages of development, too high to invest or issue loans. Therefore, the developers must finance the exploration stage with own assets or find financiers that are willing to take higher risk. Over the last few years, developing agencies have focused on assisting with financing this part of the geothermal development, offering grants and soft loans to bridge the gap. One option in lowering the initial financial risk is to use deep slim wells (small diameter) for the exploration. This has advantages when keeping the initial budget lower and easier to arrange. This can be more easily implemented, especially in areas that are considered riskier, resource wise, than better known areas due to indecisive surface exploration data. This approach can lower the cost of confirming or not the potential resource in question. In general, the smaller the diameter, a smaller drill rig is required, which translates to lower drilling costs, less infrastructure and smaller environmental footprint. It has been shown that slim wells can be tested, even though the diameter is small. They can provide similar information as the conventional geothermal wells, such as the reservoir temperature and pressure, chemical composition of geothermal liquid, gas content of the steam, reservoir permeability as well as information on the hydrothermal alteration of the geological formations. If well temperatures are high enough, discharging can be initiated and the well output measured which can be scaled up to estimate output of larger diameter wells. They may even sustain production over a longer period of time and be utilized as small producers or be used as observation wells for reservoir monitoring. Drilling slim wells may benefit the developers in de-risking their projects so that financing of the next steps of development becomes easier. If an exploration well does not prove the existence of a resource, the investment lost is less with slim wells than if larger wells were drilled. If a resource is identified and measured using slim wells, the risk of further drilling and development will be reduced significantly which simplifies decision making for developers, banks and investors.