Economics of increased bit life in high temperature wells by cooling with Top-drive Drilling System while RIH-Field results of geothermal wells and an estimate of effects for a high temperature oil well

摘要

A 540 deg C 3,729 m geothermal well, WD-1A, was drilled in Kakkonada, Japan. One major issue for drilling high temperature wells was how to protect temperature sensitive downhole tools from high temperature stagnant mud while RIH(Running-in-the-hole). To solve this problem, a TDS(Top-drive-drilling-system)-Cooling-Method was developed to drill the WD-1A well. With this ethod, mud was pumped continuously whiel running a BHA (Bottom-hole-assembly)into the hole using a TDS. To evaluate this TDS-Cooling-Method, an experiment was conducted and discovered to be very effective for cooling BHAs while RIH. (Bottom-hole-assembly)into the hole using a TDS. To evaluate this TDS-Cooling-Method, an experiment was conducted an discovered to be very effective fro cooling BHAs while RIH. Bit performance for two geothermal wells, drilled with and without using the TDS-Cooling-Method, was evaluated and revealed that the TDS-Cooling-Method could prologn three-cone bit life 5 times. Also, economic evaluation of using the TDS-Cooling-Method was made based on the field data. More than a 40% cost reduction was simulated by using the TDS-Cooling-Method when drilling the bottom 1,000m section of a 3,500 m well. Several deep, high-temperature oil wells, with ottom hole static temperatures ranging rom 180 to 230 deg C, have been drilled since 1990 in Japan by MITI, Reports are that bit life decreased to 15 to 30 hours, when the deeper sectionso f these wells were drilled. Bit performance of the MITI-Nishikubiki well was suveyed and judged that O-rings were damagd while RIH due to high temperatures. Judging from the WD-1A case, the TDS-Cooling-Method was considered to be a possible solution method to prolong the bit life. Economic evaluation of the the use of TDS-Cooling-Method was made fro the MITI-Nishikubiki well and determined that a 56 million yen cost reduction could be achieved by using the TDS-Cooling-Method if applied for the last 600 m section. TDS-Cooling-Method can be expected to extend the use of temperature sensitive tools and prolong their life for both geothermal and oil wells. Therefore, even greater cost savings can be expected in addition to those simulated.