• Karpekin, Yevgeniy
• Daungkaew, Saifon
• Fadhil, M. Imran Bin M.
• Razman, Nur Faradilla Bt. M.
• Nasifi, Wahyudin Bahri
• Yogapurana, Erik
• Rahman, Rasheed
• Thanh, Tung Huynh
• Duangprasert, Tanabordee
• Herianto, Bambang
• Pokhriyal, Krishna

Abstract

<jats:sec><jats:title>Abstract</jats:title><jats:p>In three appraisal wells that targeted carbonate reservoirs, formation evaluation was performed with conventional triple combo, borehole image, nuclear magnetic resonance logs, and Wireline Formation Tester (WFT). Several zones with hydrocarbon shows were identified, but the level of saturation was found too low to promise oil flow. Downhole testing tool was used as a primary mean to confirm hydrocarbon presence by evaluating pressure gradients and direct interval testing. In the second well, downhole fluid scanning confirmed water flow in most of the permeable intervals, but in several intervals low permeability limited extended testing time where fluid ID was not conclusive in differentiating mud filtrate from formation water. Subsequently DST was conducted in three intervals of well-2 based on identified potential oil zones from the logs and information gathered in the first well. Testing confirmed water in two zones, however the third, relatively thin zone tested oil. Standard quick-look saturation interpretation gave low oil saturation and significant volume of free water in the oil-tested zone what contradicted the DST result. As the field goes into the development stage, the need to overcome limitations of the conventional evaluation methods demanded further refinement of evaluation program and log interpretation techniques for Low Contrast carbonate formation. Further analysis of image and magnetic-resonance logs indicated different rock fabric across the three tested zones, with pore geometry ranging from vugular to interparticle type. The oil-tested zone was found to have higher irreducible water saturation and higher clay content than other two zones. A non-conventional saturation equation based on the connectivity theory was applied with in-situ clay conductivity calibration. The new saturation matched better NMR irreducible water saturation, and the overall evaluation became conformant to the DST results in all three zones. In the last well, anticipating presence of thin reservoirs with low permeability, the evaluation program was modified to include downhole testing tool with a new probe type that suits better tight formations and that permits faster clean-out and sampling of formation fluid. With its help, a thin rim of oil was discovered below the gas cap, fluid contacts were accurately delineated with in-situ fluid density measurements.</jats:p><jats:p>This paper aims to show the learning curve in data acquisition and interpretation during the exploration drilling campaign, where measurements and evaluation methods were optimized to overcome formation evaluation challenges, to identify all hydrocarbon accumulations, and to provide accurate assessment of the reserves.</jats:p></jats:sec>

Topics

• density
• pore
• resistivity
• theory
• permeability
• size-exclusion chromatography
• Nuclear Magnetic Resonance spectroscopy