Deepest Geothermal Well in Indonesia: A Success Story

Abstract

In geothermal, there are a lot of researches suspecting that there is another layer of reservoir deeper than the usual layer which has higher temperature and pressure. Particularly in Chevron Geothermal Indonesia, the layer of reservoir deeper than the present commercial layer in -5,500 ft.sl has not been reached yet. It would be a “moon landing” if the technology and specific drilling practices are founded to reach the reservoir. In 2012-2013 Drilling Campaign, Chevron Geothermal Indonesia (CGS), AWI 9-9 was drilled to depth 10,402 ftMD/ 10,007 ft TVD (elevation -6,701ft.sl). It is one of the deepest geothermal well in Indonesia to date. The objectives of Awi 9-9 were getting the steam supply and testing the temperature and permeability at depth in the southwest area of the Salak field to confirm the presence of a deep commercial reservoir (i.e. below elev. -5,500 ft.sl). During drilling, CGI drilling team observed that the key challenges to drill deep geothermal well are high temperature and total losses, which results high risk of stuck pipe. Furthermore, CGI drilling team also found out that the key success factor to drill deep geothermal well is not only reducing the risk of having stuck pipe, but also extending the 12-1/4” hole section. Stuck pipe will have very serious consequence since the team might lose the well. In order to reduce the risk of stuck pipe, we need to deal with both high temperature and total losses. In AWI 9-9, the wellbore temperature was expected to be higher than 650 deg F and it will be drilled to proven permeable zone. To cope with that, the drilling team used high temp mud motor, high temperature EMT tool and PWD tool, two mud cooler, and high temperature bit with extra protection to increase bit reliability. To take care with the total losses, the drilling team used aerated mud modelling and defensive drilling. Extending 12-1/4” hole section will make team have more flexibility by providing contingency section in deeper part to drill the deep section. However, it will increase the risk of stuck pipe. In AWI 9-9. the team successfully drilled 12-1/4” hole section as per plan, drilled to 9702 ft MD (5388 ft length), completed with 2 bit run and also this is the longest 12-1/4” hole section ever drilled in Chevron Geothermal Salak. Several best practices that team has captured to deliver of successful of drill deeper in the next project is BHA design optimization and higher temp motors. Beside of that, aerated drilling, defensive drilling, close monitoring of torque and drag and two mud coolers in drilling fluid system are other key success factor that need to be considered for next project campaign.