Radical Approach to Water Injection Scheme for Barton

Abstract

Fractured injection is not new to the oil and gas industry, and occurs unintentionally in most water injection schemes. However, deliberate fractured water injection is usually not evaluated upfront in order to derive optimal cost and recovery, and open-up opportunities for further optimization. The initial design for water flooding in Barton was based on a full-blown conventional water treatment plant on a new platform for seawater injection under matrix conditions. Fracture simulation work revealed that in the case of Barton, by relaxing water quality induced fractures are not expected to be excessively large and cause any concerns on integrity of the reservoir and nearby wells. Owing to a lower required injection tubing head pressure than previously believed to achieve fractured injection only relatively low pressure and cheap injection pumps are required. Additionally, fractured water injection has allowed for the introduction of raw-seawater injection, whereby the significantly smaller water treatment facility than previously required for matrix injection is placed on a deck extension from an existing platform. Introduction Barton Field Shell Malaysia Exploration & Production (SM-EP) operates the Barton field, which is located about 220 kms northeast of Labuan island, offshore Sabah, in Malaysia (refer to Fig. 1). The field is part of the North Sabah 96 Production Sharing Contract (PSC) with 50% SM-EP and 50% Petronas Carigali (PCSB) equity interest. Development of the field started in 1981. Oil production is primary depletion assisted by continuous gas lifting. Reservoir drive mechanism is gravity drainage with weak aquifer support. Current oil production is about 6.0 kbpd, from 11 wells (13 producing strings) at two separate platforms (BTJT-A and BTMP-B). Gas production, totaling some 3 MMscfd, is re-injected for disposal or used for gas lifting, with the excess flared at location. Geologically Barton reservoir is an asymmetrical anticlinal structure bounded by major reverse faults, and compartmentalized into 4 separate blocks. The field is situated in a structural province characterized by intense compressional wrench tectonics and clay diapirism. The reservoir is believed to be of lower coastal plain origin. Reservoir sands comprise of channels, crevasses, and shallow marine and delta front complexes with shale deposition in flood plain environment, which now form seals and flow barriers between sand units. Barton sandstones comprise predominantly of quartz, with minor content of feldspars, carbonate minerals and clays (mainly non-swelling type - kaolinite, chlorite and illite). Average porosity of the main sand package is about 20%, with rock permeability ranging from 50–3000 mD. The H sand unit has the highest rock permeability in the field. There are 3 sand packages in Barton:shallow D sands at 1000 ft tvdss charged with 16° API medium viscous oil,F, G, H and I sands at 2000 ft tvdss charged with 32° API oil, anddeeper M, P and Q sands at 3300 ft tvdss charged with 32° API oil. The current field STOIIP is about 165 MMstb, out of which some 50 MMstb has been produced. Production is almost exclusively from the G, H and I sands (main package). Fig. 2 shows the top structure map of H sand and cross sectional view of the field (along the North-South plane). Barton Water Injection (BTWI) Project Primary depletion alone addresses some 35% of oil recovery. Secondary recovery via water injection is expected to add another 15 MMstb of reserves, improving recovery to more than 45% and prolong field life. Field reservoir pressure will be progressively increased to near initial condition (c.1000 psia). Reservoir simulation work revealed that the maximum amount of seawater required is approximately 40 kb/d for optimum recovery under water injection through 4 injector wells. Each injector well is designed to handle 10 kb/d of treated seawater.

Greenhouse gas forecast in Barton Water injection reinstatement project

“…The water depth in this area is approximately 130ft. The Barton field is part of the North Sabah 96 PSCs, is valid until 31 st December, 2019, with 50% SM-EP and 50% Petronas Carigali (PCSB) equity interest [1][2][3] At present, many oilfields have reached the secondary and tertiary recovery period. According to the provided statistics, there are about millions tons of oily waste water having yet to be handled.…”