Publications

Gumai Formation is the most prolific reservoir and the primary exploration target in South Sumatra Basin. Marine conditions were established during the continuation of a transgression sequence that led to open marine facies deposition in Early Miocene. Sandstones thickness and quality increased significantly in the Gumai section as marine conditions transgressed regionally in the basin. Development phase of Betara Complex area had only assumed hydrocarbon reservoir at Lower Talang Akar Formation (LTAF) since 2001 before Gumai potential was ever proven. As part of continuous exploration effort PetroChina drilled NEB Base-1 exploration well in 2013 penetrating over 3000’ MD/2000’ TVD trough basement target. Unexpectedly, Drill Stem Test (DST) showed 4.45 MMSCFD gas & condensate flowed from Gumai Formation with 0% CO2 content, opening an opportunity to develop new potential in Betara Complex area. Following the success of NEB Base-1 testing, a study of Gas While Drilling (GWD) behavior is conducted in all of existing wells to obtain new potential zones and improve integrated reservoir interpretation in Gumai Formation. Data integration of mudlog and geophysical interpretation is required to tackle limitation of conventional wireline logs in Gumai interval. Over the course of the study potential zones become apparent when GWD of more than 267 units is applied on Southwest to Northeast well-to-well correlation. The zones are correlatable with reservoir characterization encompassing petrophysical analysis and seismic attribute of the Intra Gumai Formation. Furthermore, blind well test performed by applying correlation and integration amongst mudlogs and DST data has proven the reliability of the method and satisfies Gumai laminated shaly sand reservoir distribution in Betara Complex. All in all, GWD classification method provides justification of reservoir potential and success ratio in order to unlock and de-risk the overlooked play potential.