| Abstract |
Ulubelu field geothermal system is water dominated with reservoir temperature ranges from 250°C to 260°C. The main drilling target is reservoir target with depth respectively 1250 mMD / 1250 mTVD; 1500 mMD / 1500 mTVD dan 1800 mMD / 1800 mTVD. Typical rock types in geothermal reservoirs include granite, granodiorite, quartzite, greywacke, basalt, and volcanic tuff. One of the problems that is often found in geothermal drilling is loss of circulation, where the drilling fluid is lost into the pores or fractures in the drilled rock formation. The material and rig operating costs caused by these problems often account for a quarter or more of the total drilling costs. At non produced intervals, the circulation lost zone must be closed so that the borehole can be casing and cemented to the surface. The placement of lost circulation material (LCM) is quite difficult because the depth of the top and bottom of the lost circulation zone is unknown. LCM or cement used to cover the lost circulation zone often moves from the targeted zone to another lost circulation zone as drilling continues. In the Ulubelu field, the most problematic zone was found on the 17.5 '' hole route with depth intervals of 1117 m to 1239 m, and cementing was carried out eleven times to overcome this problem.in geothermal drilling, fractures occurred in the hole is unpredictable, whether it is continuous or limited. 1. Diaseal-M represents high solid and high filtrate that is effective in a limited number of fractured, so as to give space for Diaseal-M forming such a plug cake in the fracture. However, in geothermal drilling, fractures occurred in the hole is unpredictable, whether it is continuous or limited. To find out big or small the fracture in the hole is, it can be indicated by the magnitude of rate lossoccured. If partial loss found to be 0-2 bpm, the possibility of fracture found is small. So it is effective to spot Diaseal-MAt the time of pumping and squeezing Diaseal-M, it should be better to utilize cementing unit, because it is more effective in controlling pressure rate. In terms of cost consideration needed for Diaseal-M and cement plug activity, there is no significant difference. However, in terms of time, Diaseal-M is more effective, because it can be pumped using drilling bit assembly, so that it doesn’t spend so much time to replace BHA assembly with OEDP assembly. |