Publications

This paper is a case study done by Hess Indonesia in its efforts to optimize vertical well placement in a thin oil rim and oil-wet carbonate reservoir in Ujung Pangkah field. There were two objectives for the well placement: minimize water production and maximize oil output. The field is located just offshore, north of Gresik, East Java. The reservoir is a reefal carbonate system within the Kujung-I interval member of the Early Miocene Kujung Limestone. The oil column varies in thickness from 60 up to 90 feet including the transition zone. This oil rim is overlain by a thick gas cap.Oil production has been below the target as a result of early water production and constrained by limited water handling capability. Utilizing lesson learns from the placement of early wells that resulted in early water production, and recent special core analyses (SCAL), this study was undertaken using a conceptual sector model that took into consideration the apparent oil-wet nature of the reservoir indicated by SCAL data, height of transition zone, oil column thickness and length of the lateral section. The optimum well placement of the horizontal section is determined from the predicted cumulative oil production and is a function of the wettability of the reservoir. For an oil-wet system the optimum horizontal placement is 85% of the distance above the oil water contact to the gas oil contact. For a water-wet reservoir that optimum distance is 65%.A study conducted in two appraisal wells had misled early development execution as all cores were taken in the gas column, and gas behaves as a non-wetting fluid. Aging studies using native crude oil on core samples should have been done to better characterize the wettability. The implementation of this revised methodology in the last two wells drilled from the Wellhead Platform A has resulted production performance, consistent with the predictions from Nodal analysis.