A Unique Experience of the Evolution of the Bit Technology and Application Experience through 20 years of Tunu Field Development, Indonesia

Abstract

Abstract The bit technology has evolved dramatically over the last 20 years through innovative techniques. New bit technologies have also allowed the introduction of improved drilling parameters. In the late seventies, the introduction of PDC bits generated impressive changes in the drilling performance. Later, in the eighties and the nineties, the continuous improvement of the understanding of the fixed cutter bit behavior, and the PDC cutter technology, opened a new era and consistently lead to better results. Alongside these striking events in the PDC bit development, the roller cone bit technology showed significant improvements in both the bearings and the cutting structures. These results and the evolution of the technology are clearly illustrated in the bit performance experienced in the TUNU field, Indonesia. Over 200 wells have been drilled on TUNU since the exploration began in the mid seventies. Innovative designs were used for the optimization of the performance, the latest proven technologies were applied successfully. Over the past two decades, bit related performance has improved almost 10 times in the TUNU field. The lithology of the TUNU field at the top of the intermediate section consists of soft to very soft, sand and Claystone. Through this section the hydraulic behavior of the bits was a key factor affecting their performance. Below this zone, the formation is composed of medium strength sandstone and shale. Very hard dense dolomite and limestone stringers are encountered erratically throughout the interval. A high level of vibration, leading to catastrophic failures was typically observed throughout this zone. The first roller cone bits run in TUNU gave run lengths no greater than 250 m, and an average ROP never exceeding 6 m/h. In the early eighties, the introduction of the first PDC bits led to spectacular results where more than 250% gains in ROP and meterage were achieved. In the early nineties, roller cone bits fitted with metal face seal and new cutting structures allowed, for a short while, to see roller cone bits drilling at lower cost than PDC bits. The first anti-whirl bits tripled the run length and doubled the ROP. Later, successful runs of steel body unbalanced bits provided an additional gain of 20% in the performance. Today, force balanced steel body PDC bits indicate that drilling this section with one bit and an average penetration rate of 45 m/hr is a reality. Globally, the average penetration rate and meterage drilled per well improved almost by eight times and the trip time was also reduced drastically. In the intermediate section, the total saving per well is close to 1,000,000 US$. The cost per meter has dropped from 470 $/m to around 70 $/m. For the field, through the various phases of drilling, when comparing the performance of the first wells, and thanks to a continuous and active engineering follow up, more than 80 M$ were saved.