A Success Strategy to Producing Thousands BOPD in Complex Pressure and Drive Mechanism Reservoir Conditions with Highly Uncertainty of Faulted Architecture Field in Rokan Block, Central Sumatera Basin

Abstract

Depleted reservoir is becoming one of the challenges to be faced in mature oil field, especially when the pressure depletion is likely to fast comparing with similar oil field characteristics. TLN field (one of the prolific oil fields in the Rokan Block, Central Sumatera Basin) was one of successful example related to rapid reservoir pressure depletion. Pressure depletion in TLN field especially in MB block area was observed pretty rapid by latest pressure surveillance which caused by significant fluid withdrawn since 2003, which provoke to saturated reservoir conditions. Surprisingly, these depleted zones contributed 70% of total TLN field original oil in place and at its prime reservoir condition, MB block area was major contributor for oil production in TLN field particularly from PMT sands. This success story was accompanied to fulfill PT. Pertamina Hulu Rokan additional production and part of the 2021-2022 drilling campaign which two wells are proposed in TLN field. TLN field location approximately 30 km to the northwest of DRI field, which both operated by PT. Pertamina Hulu Rokan since August 2021.

To manage the dynamic and geological uncertainty of TLN field, which led to success of producing thousands of BOPD in 2020-2021 drilling campaign, we develop a certain strategy that suits in TLN field. From the geological aspect, we re-utilize the fault interpretation to mitigate havoc in development and execution stages using seismic reprocessing, seismic enhancement, and seismic attributes. As mentioned above the dynamic characteristics of TLN MB Block reservoirs are quietly challenging due to the pressure depletion led to the high gas oil ratio, which can be observed from drive mechanism plot of TLN Field. Likewise, the combination of weak water drive mechanism and solution gas drive that both works in TLN field is a challenge to be mitigate before well execution begin. With robust subsurface concept that applied when develop these two proposed wells in TLN field and combining with reservoir management strategy when well execution began such as, producing only from single sand and considering ESP design to be installed with gas separator, we successfully to produced additional oil gain of approximately ~2800 bopd and unlocking future potential strategy to develop MB block of TLN field, respectively due to low reservoir pressure.

As a lesson learned, we realized several strategies from geological aspect such as re-utilize the available seismic and generating seismic attribute similar like coherency to get higher resolution of fault plane location and fault continuity to mitigate the  tructural uncertainty in developing and further when execution phase begins. Moreover, a robust reservoir management is mandatory to overcome low pressure reservoir which can lead to high gas oil ratio must be managed appropriate to avoid gas production instead of oil production.