Revisiting and Expanding the Application of Dc-Exponent Method: A Successful Fault Identification in a Sub-Thrust Exploration Well in Sanga Sanga Axis, Kutei Basin, Indonesia

ABSTRACT: The dc-exponent is a traditional method used for pore pressure analysis, known for providing latest depth assessments during drilling. It utilizes drilling parameters such as Rate of Penetration (ROP), Revolutions per Minute (RPM), and Weight on Bit (WOB). In this study, the dc-exponent demonstrated its effectiveness in detecting pore pressure, especially in wells with high subsurface uncertainty, and was also proven to be reliable for fault identification. Deviations from the normal compaction trend (NCT) indicated potential fault zones. In the exploration well P-1, located in the Sanga Sanga axis of the Kutei Basin, Indonesia, the dc-exponent was employed to detect faults in a sub-thrust geological setting. During drilling, negative deflections in the NCT were observed at the expected fault depth, suggesting a possible fault zone. This was later confirmed through wireline logging tools, which validated the fault zone depth identified by the dc-exponent. The method, aside from its primary use in pore pressure analysis, proved successful in fault detection during drilling operations. This method has been applied as a new guideline in some exploration and development wells in Sanga Sanga Axis. It is expected that dc-exponent could be reconsidered as a robust method for expanding its usage in the pore pressure, analysis and fault detection. 1. INTRODUCTION The onshore of Sanga Sanga Axis, Kutei Basin, is located in Mahakam Delta, Eastern Kalimantan, Indonesia (Fig.1. and Fig.2.). The basin is the second largest hydrocarbon producers in Indonesia after Central Sumatera Basin and the largest gas producers (Ramdhan & Goulty, 2011). These fields are mature areas for hydrocarbon exploration and production, and has effectively produced oil and gas since 1976. The development area extends from the Samboja Field in the south to the Lempake Field in the north, and includes the Sanga Sanga and Semberah Fields, which mark the northern limit of the region's productive extension in the Kutei Basin.