SUCCESSFUL STORY OF PROVING-UP A NEW PLAY, AN EOCENE CARBONATE AS A NATURALLY FRACTURED RESERVOIR IN OFFSHORE NORTH WEST JAVA

摘要

The excellent production performance of the K-85 zone (Pre-Talang Akar Formation/TAF) in KLD Block of the Offshore North West Java (ONWJ) PSC has triggered a comprehensive study to seek new opportunities in the adjacent block, called KLA Block. The zone was originally called as basement but further petrography analysis showed that the lithology is limestone deposited in Eocene based on age dating. It has no primary porosity and permeability due to high effect of compaction. Five of thirteen penetrating wells experienced total loss circulation (TLC) during drilling. Hypothetically K-85 zone is considered a naturally fractured reservoir which can explain this TLC phenomenon. This paper will mainly discuss the challenges, method, lessons learnt and drilling results of this successful story. Hydrocarbon existence, resources determination, fractured characterization and production performance prediction has become the main challenges. Existing data such as the drill stem test (DST) test of K-85 has also been performed in an exploratory well within the K-A'W'est Block and showed an inconclusive result that must be verified. Revisiting and reinterpretation several data such as old-wells cutting samples mud log data, seismic and production data from existing wells can provide higher assurance. The material balance (MBAL) data and back-calculation approach from the producing adjacent block was then used as analogue data for resources determination and production performance. Discontinuity feature in seismic has high correlation with the depth of total loss circulation in the offset wells. It raises the prediction accuracy of fracture distribution in K-85 reservoir. Two dependent wells were originally proposed targeting the K-85 zone in West Block and were planned to prove the hydrocarbon accumulation. Well trajectory was designed penetrating perpendicular to the main fracture orientation. The first well has been drilled and successfully tested with initial rate close to 10 mmscfpd, 1800 bopd at WHP 2000 psi, followed by the second well with a similar rate with no water. It raises field production by more than sixty percent and becomes the new backbone for gas and oil production. This is the first successful story of proving up an Eocene Carbonate as a naturally fractured reservoir in Offshore North West Java.