ABSTRACT
"E" field, located approximately 20 miles offshore Java in the Northwest Java basin, is a horst block reservoir bounded by well defined faults with the southern side open to aquifers of varying size and deliverability. E field contains two principal hydrocarbon bearing zones known as the Main and Massive formations. These two litho-stratigraphic units contain four separate producing intervals. The reservoir covers over 3500 acres and has 700 MMSTB oil originally in place (OOIP) with a current recovery of 26% OOIP since production began in 1971.
A multi-disciplinary team with personnel representing petrophysics, geology, geophysics, and reservoir engineering disciplines was formed to understand past performance, evaluate future development options, and provide a reliable forecasting and field surveillance tool. A detailed three-dimensional three phase full-field reservoir simulation model was constructed using a fully heterogeneous reservoir description. The primary reservoir depletion mechanisms for each producing interval were identified through history matching. Differences between zonal recoveries were attributed to variations in sand quality and continuity, gas cap size, and aquifer size and deliverability.
The integrated reservoir study was conducted in two phases. The first phase re-evaluated a planned multi-zone waterflood and the second phase focused on an alternative plan of development Results of the phase one study indicated that the waterflood as proposed was not optimally configured. It over emphasized the high recovery upper reservoir intervals at the expense of the lower intervals and its proposed peripheral displacement slowed waterflood response. In addition, the proposed down-structure peripheral injection program had high associated costs due to long piping runs and other facilities considerations. A dispersed injection program selectively targeting low recovery reservoir intervals improved early time rate response and provided larger reserves than the peripheral waterflood program.
Incremental analysis of the phase one results showed that infill wells accounted for about two-thirds of the waterflood case reserves. Economic evaluations indicated that the infill case (without water injection) yielded a higher rate of return and greater present worth per dollar invested. Therefore, a staged infill development program was adopted in phase two of the study as an alternative to the waterflood resulting in significant cost savings.
Ongoing studies, evaluating various low volume waterflood configurations in conjunction with infill well development, are underway. This work is being conducted with cost-benefit analyses to determine the optimum economic development program for E field.
This paper documents simulation model development and application. Forecast sensitivities supporting the phase one and phase two portions of the study are presented. In addition to the waterflood and infill well sensitivities, gas development opportunities were also evaluated.
