Make-Up Well Selection for the Darajat Geothermal Field, West Java, Indonesia

Abstract

A make-up drilling campaign was implemented at the Darajat field in 2007-2008 in order to maintain full generation at 260 MWe until 2010. Decline analysis indicated that the make-up well needed to produce at least 160 kg/s steam. A preliminary analysis based on the average well production rate in 2006, which was 25 kg/s, indicated that up to eight wells would be required. In order to maximize the value of the drilling program, an attempt was made to achieve the most productive wells at the lowest drilling cost. A large portfolio of wells was developed that targeted wells from existing production locations. To determine an expected steam production rate for each well in the portfolio, correlations were established between well productivity and five targeting elements: hole angle, hole azimuth relative to open fracture orientation, lithology, entry elevation, and targeted production zone. A proxy for probability of success was developed from these targeting elements which could be correlated to expected well productivity. Eight wells were selected from the portfolio with an expected steam production of 231 kg/s. Seven of these wells were drilled, with one requiring a redrill, yielding an estimated total production of 266 kg/s steam. The drilling results demonstrate the success of this targeting and well selection approach.