Publications

The complex structural framework of the Central Sumatra Basin (CSB) has resulted in a transtensional compartmentalisation in mostly oil fields in WK Rokan, such as the Tilan field. CSB’s intense tectonism led to many troughs, including the North Aman Trough, where the Tilan field is located. Portraying the North Aman framework, the Tilan field has a geometry of a half-graben block with a three-way structural trap. These complex structural frameworks come with a shortfall in seismic interpretation due to the low quality of the available seismic volume, resulting in drilling issues caused by structural uncertainty. Tilan field is separated into two blocks, the Main block, currently the main contributor to the field, and the SE block, which currently has a low reservoir pressure. Faults in the Tilan field likely propagate into a relay-like structure; theoretically, the stress and strain interfere with the surroundings and become a structural uncertainty in developing this field. Structural uncertainty was identified when additional infill wells (wells A and B) were proposed for the 2021 program. Previous seismic interpretation had already identified the fault markers from existing wells and enhanced the seismic volume by phase rotation to interpret the uncertainty fault envelope. These wells were planned to drill with a highly deviated trajectory alongside the fault; at this point, real-time logging was chosen for the drilling program. Unfortunately, well B was crossing the fault in the upper section of the sand target. Loss circulation was challenging but was stopped by optimising the mud weight. The trajectory was steered back in the footwall block to recover the lower sand target. Subsequently, after updating fault markers, re-interpreting the fault plane, optimising the well plan, and generating a seismic attribute called Thinned Fault Likelihood (TFL), we executed the next well without drilling issues and obtained tremendous additional oil gains.