Abstract

Designing an effective development strategy in aging oil fields is critical to ensure production until the last drop of oil can be economically produced. Yakin Field, a relatively small, 24 year old oil field in East Kalimantan, was predicted to be near the end of its lifetime when the total cumulative production of this field had reached more than 39 MMBO in January 2000. Average production had declined from a peak rate of 14,000 BOPD to 5,000 BOPD with an average water cut of 50% from 30 wells. Recently, an integrated multi-disciplinary project to quantify remaining reserves revealed oil potential that will extend the lifetime of this field.

An integrated mapping approach was utilized to compile and evaluate geological, geophysical, and engineering data and to calculate reservoir volumetrics. Utilization of 3D seismic, well and production data, and newly acquired reservoir pressure data were essential elements to this approach. Reservoir units that are highly compartmentalized by complex normal and thrust faulting show differential depletion and were immediately recognized. Reservoir juxtaposition commonly occurs along fault planes where fault throw is less than reservoir thickness. However, different original fluid contacts and pressure differences between fault blocks strongly suggests that fault zones are semi permeable to sealing. Vertical fluid movement due to production is observed, indicating a relatively high vertical permeability within reservoir units despite the presence of intercalated clay layers. Drive mechanisms range from depletion to strong water drive. As a result of the identification and understanding of these reservoir complexities, a number of potentially undrained small fault blocks within the field were identified. The need for a waterflood program was also recognized to support closed systems where pressure depletion occurs.

A gradual increase in daily production from Yakin Field started immediately after the first drilling campaign. This initial program was executed in mid 2000 in the Yakin North sub-thrust fault block. The program consisted of 3 long reach horizontal wells and 3 deviated wells. The long reach horizontal wells were designed to meet economic hurdles by penetrating and draining adjacent small fault blocks. To date, a total of 12 wells have been drilled and 7 additional locations have been added to the inventory list.