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Geology and Geomechanics Evaluation of CCS Pilot Project in The Gundih Field, East Java Basin, Indonesia

Abstract

The first Indonesian Carbon Capture Storage (CCS) pilot project will be conducted in the Gundih Gas Field, Central Java Province. This field has been in production since the end of 2013 with CO2 content is 21% of the produced gas. 15% of the total produce CO2 will separated as pure CO2 in Central Processing Plant (CPP) which equivalent with 800 tones per day of CO2. The gas is produced from the 3 main structures, which are situated inside the Gundih field, namely Kedung Tuban, Randu Blatung and Kedung Lusi, which can produce around 60 MMSCFD within 12 years. This paper is presented results of geological evaluation for selecting best geological CO2 storage location in the Gundih Field. Gundih field is located in the onshore part of the East Java Basinal area part of Java island back-arc basin. Regionally, it is part of the Central High characterized by E-W trending ridges bounded to north by Sakala Fault Zone and to the south by anticlinorium of Kendeng Zone. It's surrounded by several others oil and gas fields including the famous Banyu Urip (Cepu Block). Two of the most famous reservoirs are clastic and carbonate of Oligo-Miocene Kujung Formation (deeper reservoirs) and Miocene sandstone of Ngrayong Formation (shallow reservoirs). Geological evaluation of CCS pilot project is conducting using integrated surface geological mapping, core from two shallow drilling and subsurface data (2D seismic and wells). The target formation for CO2 storage is Ngrayong formation, which is composed of sandstone and lies at a depth of 830 – 1200 m below the surface in order to have CO2 in supercritical condition. The target structure known as JP structure near JP-1 well, which is located approximately 22 km to the north of the CPP/Gundih structure. JP-1 is a suspended well which can be used for CO2 injection as long as the JP structure is safe to store the injected CO2. The JP structure is a small anticlinal structure bounded by high-angle reverse fault, which could store more than 6000 × 103 m3 of CO2. Cap rocks consist of thick carbonate mud (mudstone) of Wonocolo Formation which excellent due to their ductility characteristic and low permeability. Fault seal analysis indicated sealing behavior. Limited geomechanics analysis suggested that fault strong enough for holding large pressure difference due to injection. In conclusion, this study indicates that JP structure is large and safe enough to be considering as the best candidate for conducting CCS pilot project.