Bokor: Development and Technology Challenges of a Mature Field

Abstract

Abstract Development for further opportunities in a mature field offers a unique set of challenges. The approach to this requires a focused multi-disciplinary team to arrive at a proper understanding of the reservoirs and the right technical solution. These challenges were experienced in the development of the Bokor Field, located 45 km northwest offshore Lutong, Sarawak in the Baram Delta region. The Bokor Field is featured as a simple domal uplift with a collapsed crest superimposed onto a rollover anticline resulting from growth faulting. The field is deposited in a series of multiple stacked deltaic to shallow marine sandstone reservoirs that contain both oil and gas. The field was discovered in November 1971 by BO-2 but was put on production only in 1982. The reservoirs were completed commingled to maximize completion strings' utilities and production from the stacked reservoirs. Limited spare well slots and unconsolidated reservoirs which often hinder further development in the past has ignited a flurry of technical creativity in the application of new technology. Due to development strategy of placing wells clustered at the crest of the domal structure in the past, the extent of the structural flank limit of the field is still relatively uncertain providing further future appraisal opportunities. The current field activity is mainly related to maximizing oil recovery and further development opportunity identification. This paper discusses how it is possible to turn around a "brown" field by identifying the occurrences of the bypassed oil and at the same time replenishes reserves from the appraisal targets. It will also highlighted on the effectiveness of the new technology that has been implemented in the Bokor Field; from multi-lateral to "Triple wellhead" technology. This technology has allowed more reserves to be developed with fewer wells. Introduction The Bokor Field is one of the nine fields operated by PETRONAS Carigali Sdn Bhd. in the Baram Delta Province located 45 km offshore Lutong, Sarawak (Fig.1). It was discovered in October 1971 by well BO-2 after the unsuccessful exploration well BO-1 in 1967. Commercial oil production started only in December 1982 from BODP-A. To date there are three drilling platforms in the field, namely BODP-A, BODP-B and BODP-C. With undeveloped reserves and bypassed oil still aplenty but hindered by limited spare well slots, an innovative drilling technology was applied in the field. The world first "trilateral well" was drilled in 1996 followed by another world first "triple wellhead with dual string" in 1999. Elsewhere in the Baram Delta province the country first Twin wellhead well was implemented in the Tukau and Baram Field in 1998. The other challenges for the Bokor field are the shallowness of the reservoirs (the main reservoirs are less than 2000 ftss), unconsolidated loose very fine sand, thin stacked reservoirs, heavy crude and the field structural uncertainties. CMR log introduced as a pilot project in the Bokor field in 1999 has allowed previously interpreted tight reservoirs to contain mobile oil now. With the introduction of numerous new technologies and new well data, the STOIIP of the field has increased tremendously from as low as below 100 MMSTB in the early 70's to almost 800 MMSTB currently. Regional Geological Setting The delta progradation has resulted in the formation of sand-dominated clastic wedges, which characterizes the whole of the Baram Delta Province. The Bokor reservoirs are located in the middle of this clastic wedge. This comprises a series of north-westward prograding, sand-dominated units separated by thin, laterally extensive, transgressive marine shales. Since Middle Miocene times, the Baram Delta has been subsiding relative to the Central Luconia Province along the major NW-SE trending West Baram hingeline. The compressional deformation culminated during the Late Pliocene. The location of commercial hydrocarbon accumulations coincides with the intersection of growth fault trends and the main compressional anticlinal axes.