Stuck Pipe Prevention in Geothermal Drilling

Abstract

Stuck pipe is one of the main issues in the geothermal drilling industry mainly due to the nature of geothermal field and this has to be resolved. In this paper, we will be using basic scientific methodology of problem solving to resolve the issue. Step 1 is to define the problem, which is the stuck-pipe incident in this case. Step 2 is to identify causes. Fundamentally, there are three basic causes of stuck-pipe: wellbore integrity (pack-off), differential sticking, and hole geometry. It is known that stuck-pipe in geothermal well is mostly caused by pack-off. The nature of geothermal field are having subnormal formation pressure and having existing natural fracture. Whenever this subnormal pressure fracture is intersected, partial or lost circulation would occur. Cutting will then build up across the wellbore and ready to pack-off the drill string at any time (stuck-pipe). Step 3 is to formulate the solution. Several solutions have been initiated by the team. Introduction of aerated drilling to minimize the overbalance between wellbore ECD and formation pressure which will help to cure the lost circulation, Use of UBD Pro software to model the aerated mud while drilling, better solid control system, and casing program optimization. Step 4 is to implement the solution. The team has put continuous effort to implement and monitor the proposed solution during the drilling campaign. Step 5 is to evaluate the solution. Statistic has shown the number of stuck-pipe incident has decreased significantly from campaign to campaign. During the last 2012/2013 drilling campaign where 15 wells were drilled, number of stuck-pipe incident was very minimum. However, we believe zero incidents are attainable. Therefore, the team is still evaluating and improving.