Challenges and Mitigation Strategies for High Gas Situation during Drilling in Sapi Field

Abstract

This paper discusses the challenges and mitigation strategies for dealing with high gas situations during Sapi development well drilling operations on Pertamina Hulu Kalimantan Timur. Sapi's drilling campaign began in December 2021, with three re-drill and four new wells. Historically, the highest record of gas encountered during drilling is 4,500 U TG and 1,000 U BG without a kick sign. The Sapi-13RD1 is used as the benchmark for the high gas situation in Sapi area during this campaign. This well encountered a high gas situation while displacing the well with mud from 12 ppg MW to 12.4 ppg at 13148 ft, BG reading increased from 180 U to 400 U. This situation induces confusion among operation and also drilling program design against material stock and drilling time efficiency despite the limitation of drilling cost.. As a result, new strategies for dealing with this situation were developed. Offset well studies show that increasing MW has been shown to reduce BG Gas in some cases, but not necessarily peak gas encountered during drilling. The SAPI-1 well was drilled to TD with a maximum of 14.5 ppg MW but still encountered up to 3000 U of connection gas. Despite maintaining adequate mud overbalance (max pore pressure SAPI- 13 is 8.7 ppg from MDT log), we still encountered high gas content during drilling. Following a thorough analysis of pore pressure-related events, the drilling history of all offset wells, and responding from the drilling operation side by ensuring safe drilling, the high gas reading is not related to pore pressure close to mud weight. The decision flowchart for high gas situations during drilling was made by increasing the cut off of BG gas to 400U prior to increasing MW and setting a cut off TG 2500 U to close annular and circ gas out. This decision flowchart was used for the remaining six wells in this campaign, giving the drilling team the confidence to accept the high gas reading while maintaining safe operation in the Sapi area. This decision record is developed to give clear guidelines when encountering high gas situation during drilling to ensure that the well can be safely drilled – maintaining well control at all times - without compromising other factors when we decide to increase the MW to specific value (risk of differential sticking, losses, ballooning, cement slurry weight strategy, etc)