Problem Mitigation in Geothermal Drilling, Case Studies of Stuck Pipe and Lost Circulation

摘要

Geothermal energy is one of fast growing renewables resource in the world. Demand for renewable resources leads to increase of geothermal drilling activities. Well cost contributes up to 40 % of total geothermal project cost. Drilling in geothermal faced many challenges due to its natural characteristics. The most common problems are lost circulation and pipe stuck. Highly fractured zone is the ideal spot for geothermal production. Lost circulation is common in highly fractured formation. Stuck pipe is another problem. Stuck pipe can lead to extra cost of lost-in-hole and fishing operation. Water played an important role in geothermal drilling, not only to keep the wellbore pressure but also to cool down the temperature. This paper shows some severe cases of lost circulation and pipe stuck in geothermal drilling. All of the data are taken from geothermal drilling projects in Indonesia. The cases of lost circulation can be divided into two major type based on the location, shallow and deep lost circulation. Each has different technique to overcome lost circulation. Two cases in pipe stuck presented in this paper are the most severe incidents in geothermal project in Indonesia. Underbalanced drilling was a common application in highly fractured and subnormal pressured formation as found in geothermal. Both cases performed underbalanced drilling prior to stuck pipe incident. This paper evaluates gas-liquid flow rate based on Guo and Ghalambor (2002) criterion.