Unlock EOR Potential of Carbonat Reservoir by CO2 Injection in Sukowati

Abstract

Pertamina EP has mature oil fields that still produce in primary and secondary stages. These problems can be solve by applying tertiary or enhanced oil recovery (EOR) methods. EOR screening processes was conducted using the combination of Al-Adasani (2011) and Taber (1983 & 1997) to determine the most suited EOR methods for each reservoir. From preliminary EOR screening results showed 10 oilfields with CO2 miscible method, 4 oilfields with CO2 immiscible, and 10 oilfields with WAG method. Sukowati oil field has very good pressure maintenance due its reservoir strong water drive mechanism. From 10 years oil production only made 200 psi differ from original pressure. From its original reservoir water drive mechanism, it's expected to achieve 50% recovery factor. Tertiary program is a next stage to gain more oil production 16,8% recovery factor with CO2 EOR injection.
Sukowati is onshore field located at Tuban, Bojonegoro, East Java. The field was discovered in 2001 and start producing in Juli 2004, reached peak primary production at 44923 BOPD at September 2011, and recently at 30.04.2018 oil production has reached 6160 BOPD. Since 20 Mei 2018, Sukowati field is being operated by Pertamina EP that previously by JOB Pertamina Petrochina East Java.
Sukowati Field is top kujung tuban formation that described as tall carbonat reef build up. OOIP Sukowati is 297 MMSTB with cumulative oil production is 114 MMSTB as of 30.04.2018. It has API 39, Viscosity 0.43 cP, avg permeability 156 mD, temp 275 F, main composition C5-C12, and depth 6300 ft. With these reservoir property, regarding to the EOR Screening criteria shows the CO2 EOR was suited to be applied in Sukowati. At appropriate pressure oil hidrocarbon will make mass-transfer process CO2 dissolution and condensation that can lighter oil and moves the residual oil. This also supported by potensial CO2 Source from Jambaran Tiung Biru that located 44 km away from Sukowati with 100 MMscfd CO2 gas that will on stream at 2021.
Slim tube test has been done, full scale application will be miscible without causing fracture pressure. However, some challenges to implement CO2 EOR in Sukowati; one thick layer with gross thickness 780 ft (no gascap), uncertainty faults, and water channeling behind casing.
This paper will describe the CO2 injection program in Sukowati field. Variation scenarios already applied as reservoir simulation that CO2 injection with specific rate will show best oil production performance at incremental 50 MMstb.