Publications

Thick shaley overburden sections such as the Telisa Formation are one of the main challenges for drilling wells in the Suban Field. Prior 2012, water-based mud (WBM) was used to drill this formation, with KCl additive, resulting in low rate of penetration (ROP) and shale stability issues which requiring several bits run to successfully drill the section. Subsequently, starting 2015 synthetic oil-based mud (SOBM) was used in drilling campaign to improve drilling performance. However, the costs of SOBM are high and cuttings handling is more environmentally risky. For continuous improvement, a high-performance water-based mud (HPWBM) was designed to have a better drilling performance at lower cost and is more environmentally friendly. Several HPWBM laboratory tests were conducted by utilizing shale cuttings from several Suban wells. In general, the clays mineralogy in Suban overburden sections are predominated by kaolinite and illite. Consequently, the HPWBM formula need to be designed to handle the behavior of the clay minerals that tend to be dispersed. Based on lab results, NaCl, KCL and Polyamine need to be added to the HPWBM system. With HPWBM, the drilling ROP was predicted to have better performance than WBM but less than SOBM. This ROP prediction was used to design real-time logging data transmission while drilling (LWD). During drilling execution, the actual ROP exceeded the prediction. However, this high ROP resulted in intermittent real-time data transmission. Therefore, real-time LWD data selection needs to be carefully adjusted for the next sections. The use of HPWBM is also impacting the quality of gas readings that experienced distortion due to absorption. The absorption is caused by chemical components in HPWBM increases as the carbon component in hydrocarbon gas increases. However, the magnitude of absorption is lower than absorption in SOBM. Thus, interpreting gas logs should be done with caution.