The Suban field’s gas reservoir, located at approximately 2000 mTVDSS, is composed of Pre-Tertiary rocks including Igneous and Metasediments, as well as Tertiary sedimentary rocks like LTAF (Lower Talang Akar Formation) and BRF (Baturaja Formation). Before accessing the gas reservoir, drilling activities must navigate through overburden formations, predominantly shale-based Palembang and Telisa Formations. A particular challenge encountered within the Telisa Formation is the presence of overpressure conditions.
Historically, drilling through overpressure-prone formations has posed formidable obstacles. Earlier approaches employed water-based mud (WBM) for drilling, which encountered issues such as shale instability and slow rate of penetration (ROP), necessitating the use of multiple drilling bits.
In 2012, a shift was made to Synthetic Oil-Based Mud (SOBM) to address these challenges and enhance hole stability. The outcome was not only improved hole stability but also a noteworthy surge in the rate of penetration (ROP). Consequently, SOBM applications have been employed for drilling gas-fractured reservoirs in the Suban and Sumpal regions since 2012. However, the adoption of synthetic oil-based mud (SOBM) presented its challenges, including significantly higher costs compared to water-based mud (WBM) and challenges in handling and disposing of non-environmentally friendly drilling waste associated with SOBM.
Recent developments have introduced High-Performance Water-Based Mud (HPWBM) as an alternative to Synthetic Oil-Based Mud (SOBM) for drilling. While HPWBM is not a complete replacement for SOBM, it aims to match its performance in terms of shale inhibition, wellbore stability, and rate of penetration (ROP). Additionally, HPWBM offers the potential for cost reduction and improved drilling performance.
To incorporate HPWBM into the Suban field, a meticulous technical review and analysis were conducted to align the formulation with the reservoir’s mineralogy. The implementation was initially carried out in a specific Suban well, focusing on the 12.25" hole section due to overpressure.
Key goals in designing the HPWBM included achieving superior shale inhibition, countering clay swelling and dispersion, and maintaining stability at high application temperatures. This alignment was particularly critical in the 12.25" section to minimize standpipe pressure (SPP) and Equivalent Circulating Density (ECD) and avoid formation fractures. A comprehensive laboratory testing process led to the development of 134 HPWBM formulations, with Formula 134 emerging as the optimal choice to fulfill the required objectives.
The successful implementation of HPWBM, specifically formula 134, in the Telisa Formation marked its efficacy in delivering performance on par with SOBM. This achievement not only demonstrated cost-efficiency but also streamlined and effective drilling operations.
