| Abstract |
Drilling efficiency largely depends on bit life and rate of penetration. Three-cone bits, however, have temperature sensitive parts such as O-ring seals and diaphragms, which have temperature limitation of 150 to 190 oC, and are prone to damage by high temperature while running in the hole and during drilling. The new method was adopted to protect Oring seals from high temperature while running in the hole. Mud was pumped continuously while running a bottom-holeassembly (BHA) in the hole using a top-drive-drilling-system (TDS). To evaluate this TDS-Cooling method, two high temperature geothermal wells Well-21 and WD-1a, which were drilled without lost circulation for the 8-1/2 inch sections, were selected. The WD-1a well was drilled using TDSCooling methods, and Well-21 was drilled with conventional techniques when drilling high-temperature formations. As for the Well-21 bit performance, three bit O-ring seals survived and average drilled hours of the three bits was 28 hours. The deepest depths where O-ring seals survived was 2,105m where the static formation temperature was 350 oC. Whereas, for the WD-1a well, the depth of the last bit for which O-ring seals were still surviving was 3,451m and bits drilled for 31 hours where the static formation temperature was more than 450 oC. The average drilled hours of the 5 bits without O-ring seal failures was 50 hours, where the static formation temperature was between 350 and 450 oC. Judging from the bit performances for the two wells, bit life using TDS-Cooling method would be three to six times more compared with conventional cooling method if the same formation temperature and depths were drilled. Economic evaluation of using a TDS was made based on the field data when these two high temperature wells were drilled. Two examples are considered that compare the drilling of two 1,000 meter sections of 8-1/2 inch wellbore. Example-1: Drilling 8-1/2 inch section of the well from 2,500 to 3,500 m. Example-2: Drilling 8-1/2 inch section of the well from 2,000 to 3,000 m. The cost factors, times and bit life for each example were given based on the actual data. Simulation results show TDS-Cooling results in more economical drilling costs for both cases. The many other advantages of using a TDS are described and indicate that it will be very economic to use a TDS when drilling high temperature wells. |