Innovative Casing Drilling Technology Improved the Ability to Set the Casing Deeper Through the Problematic Zone in Indonesia Geothermal Operation

Abstract

Well A is a geothermal well in K field, located in the Jambi area of Sumatera. The pilot hole of the 17.5-in section was drilled to total depth (TD). However, a 13.375-in casing running difficulty was experienced afterwards. A dedicated cleanout bottomhole assembly (BHA) was run, but this became stuck. The decision was taken to plug the pilot hole with a cement plug and to perform an openhole sidetrack. The difficulty in running the 13.375-in casing is caused by collapsing formation from the borehole wall. The commonly run casing/liner tieback system has no rotational capability when an obstruction is encountered while running the casing. The 13.375-in × 17.5-in nondirectional casing drilling technology was proposed as the solution. The main component of this technology is the drillable alloy casing bit, which drills on standard casing that is rotated at the surface. The casing bit is equipped with PDC cutters and nozzles with the same function as those in a conventional PDC bit. The casing can be fully rotated while applying weight to cut through the obstruction. The casing drilling system successfully set the 13.375-in casing to 849.72-m measured depth (MD), 314 m deeper than the initial point of the casing running obstruction. The drilling/reaming capability of the casing bit helped in cutting all the formation filling the predrilled hole. The cementing process was executed well, with good integrity to the surface, shown not only by a surface return during the cement top job but also by a good cement bond log (CBL) result. This eliminated the requirement of having a casing/liner tieback system, which saved operating time and cost. The ability to set the casing deeper enabled sealing off the total loss zone. Consequently, the 12.25-in section drilling could be executed without penetrating the problematic zone, which improved drilling efficiency.