Shale Hydrocarbon Characterization of North Sumatra Basin, Indonesia: Revealing New Reserves of Non-Conventional Shale Hydrocarbon

Abstract

Unconventional hydrocarbon exploration in Indonesia is still in early stage. The regulation of preparing unconventional working area is still formulated based on definition obtained from the studies done by the government and adopting the existing regulation from other countries. The first unconventional hydrocarbon well in Indonesia was drilled by PERTAMINA in late 2016, located in Tamiang Deep, North Sumatra Basin. The well reaches 3,800 m TD, penetrated Lower Baong Shale with 1,900 m thickness. Laboratory analysis, such as RCAL-SCAL-XRD-SEM and G&G evaluation were undertaken to obtain comprehensive results including regional geology, geochemistry, petrophysics, basin modeling, and static modeling. The study revealed that development of basin was influenced by several structural geology elements such as Sumatran Fault and Barisan Mountain, pre-Tertiary Suture and Tertiary grabens. Paleogeography of the Oligocene to Middle Miocene shows variations of shore-face to bathyal environment for each formation. Strong marine influence persisted within the basin during Oligocene – Miocene since the basin was connected to Andaman Sea. Transgressive event during Middle Miocene deposited Lower Baong Shale in marine environment which shows a good lateral distribution within the basin. Lower Baong Shale as possible source rock contains mixed Type II and III kerogen. Sweet spot is on the edge of Tamiang Sub-basin, showed shallower basement with higher heat flow compared to Arun and Lhok Sukon Sub-basins. High-grade area is determined by TOC, porosity, permeability, kerogen type and vitrinite reflectance, brittleness index, Vclay, water saturation, and thickness cutoff. Basin modeling shows oil maturity at depth of 2,271 m of Middle Miocene, and gas maturity at 3,268 m of Early Pleistocene. Potential gas content is 104.58 scf/ton in the southern part of the Tamiang Sub-basin. Although formation evaluation has been done, horizontal drilling and appropriate well stimulation test are needed to validate the hydrocarbon flow in the unconventional zone. Keywords: shale hydrocarbon, North Sumatra Basin, Lower Baong Shale, and unconventional hydrocarbon exploration.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018