An Integrated Methodology To Locate Oil Opportunities in Mature Reservoirs

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18004, “An Integrated Methodology To Locate the Remaining-Oil Opportunities in Mature Reservoirs in Offshore Sarawak, Malaysia,” by M.J. Zulhaimi, W.M.S. Wan Ibrahim, S. Sanyal, K.A. Zamri, M.N. Mohamad, and K.N.M. Zaini, EORC; R.D. Tewari, Petronas; and A.K. Pradhan, ADCO, prepared for the 2014 International Petroleum Technology Conference, Kuala Lumpur, 10–12 December. The paper has not been peer reviewed. A matured field is currently producing with greater than 85% water cut (WC) and has significant levels of uncertainty with respect to oil/water contact (OWC), flank structure, depth of spill points, production allocation, and residual oil saturation. A robust work flow was developed to identify infill opportunities by integrating material-balance study, cased-hole-log information, water diagnostic plots, decline-curve analysis, and other information. The comprehensive locate-the-remaining-oil (LTRO) methodologies applied have been successful and have helped to estimate the potential reserves as well. Introduction The field is 20 km offshore Sarawak, Malaysia, in water depths of 100 ft. The field structure consists of a 30,000×9,000-ft elongated anticline running northeast/southwest and comprises a series of stacked reservoirs at a depth of 4,000 to 9,500 ft. The field is considered structurally simple, with a normal growth fault affecting only the deep reservoirs and no other faults visible on 2D seismic or in the wells. The field reservoirs were deposited during the Late Miocene in a lower coastal plain to the coastal environment. The depositional environment of this field is dominated by a sequence of shore-face deposits. Sands are loosely consolidated, fine- to very-fine-grained, and interbedded with layers of silts and clays. Porosity ranges from 14 to 26%, with a fieldwide mean of 20%. The permeabilities are on the order of 50 to 3,000 md. Net sand thicknesses are less than 30 ft, with most individual sands at approximately 10 ft. The reservoirs are subdivided into three categories: Shallow reservoirs at depths of 4,000 to 5,300 ft are characterized by large gas caps and mostly thin oil rims and are currently considered unfaulted. Main reservoirs at depths of 5,300 to 6,000 ft with no gas caps are also currently considered unfaulted. Deep reservoirs at depths of 6,000 to 9,500 ft can carry high pressures and are dissected by a northwestheaded growth fault with possible associated additional faulting.