Lightweight Water-Based Mud Using Glass Bubbles for Drilling a 6-in. Horizontal Section in a Gunung Kembang Development Well

Abstract

Abstract A Gunung Kembang drilling campaign recently drilled three wells with 1,510-, 525-, and 283-ft MD horizontal section lengths. The landing point of these wells is 3,200 ft TVD in limestone formations. Failures from the first and third wells resulted from a total-loss circulation problem, and drilling was stopped following an uncontrolled loss rate and a diesel-oil stock shortage. Two suspected factors are believed to be the cause of loss circulation in Gunung Kembang: 1) depleted formation pressure, which recorded 6.8 ppg and led to a narrow margin of overbalance mud weight and minimum stability mud weight, and 2) the presence of natural fractures. This factor requires further discussion owing to the geomechanic study results, which predicted several azimuths that natural fractures will most likely encounter while drilling. Water-based mud then becomes an option for drilling a 6-in. horizontal section in the Baturaja limestone formation, as water supply is almost unlimited and is easy to acquire. A non-damaging fluid in combination with a glass-bubble lightweight additive is proposed for drilling this section to 1,600 ft MD. To minimize the possibility of loss circulation, mud density is designed to be slightly higher than the formation pressure. The formation pressure is recorded at 6.8 ppg, thus the mud weight will be 6.9–7.1 ppg (17–50-psi overbalance) using glass bubbles (hollow-glass spheres). A laboratory test regarding this mud system was conducted to determine the optimum concentration of glass bubbles in waterbased mud using the value of PV so as to affect ECD and surface circulating equipment reliability. A return permeability test was also conducted against the Baturaja limestone core sample with a 15% reduction in permeability. This result offers a better solution for the Gunung Kembang drilling campaign owing to its lower operational cost and that it is more environmental friendly.