REVEALING HYDROCARBON POTENTIAL IN A TIGHT SAND RESERVOIR A CASE STUDY OF THE BATURAJA SANDS IN SUMPAL FIELD, SOUTH SUMATRA BASIN

摘要

The Sumpal Field is a large gas field located in the Corridor block of South Sumatra which currently produces from fractured pre-Tertiary age crystalline rocks. During the exploration and development program, a sandy interval in the Baturaja Formation was encountered in many of the wells. The interval exhibited a high mud gas reading indicating that it was hydrocarbon bearing but was not pursued as a development target since the primary objective was the pre-Tertiary reservoir. To determine the productivity of this interval, it was re-evaluated and tested in 2016. The case study presented in this paper highlights the evaluation of the clastic Baturaja Formation and the testing and results of this interval in the Sumpal 2 well. The Baturaja Formation in Sumpal Field is a silty sandstone which ranges in thickness from 7 to 18 meters and is interpreted to be present over 75% of the field. Mapping this sand between the wells is difficult since the 3D seismic survey over the field was optimized to image the deeper basement rocks. To determine sand distribution in the field, several hand drawn maps were created. These maps used several geological analogs which are consistent with the interpreted depositional environment of this unit. Based on the results of the interpretation and modeling, the decision was made to test the Baturaja in the Sumpal 2 well. Following perforation, the pressure slowly increased in the wellbore, suggesting a tight reservoir. The well was subsequently mini-fracked and the pressure increased a faster rate than after perforation. The well head was opened and the well only flowed completion fluid for a few hours before dying. The well was shut in and several days later after the well-head pressure increased, the well was opened and sample taken which recovered 60 cc of light oil in 3 liters of liquid. The results from the test of the Baturaja sandstone in Sumpal 2 suggests that the reservoir is oil bearing but low permeability. More innovative methods of drilling (e.g., horizontal or long reach wells) coupled with more aggressive completions (fracture stimulation) is required to fully evaluate the recoverable potential from this reservoir.