No abstract

The Baram Delta Operations (BDO), located offshore Sarawak Malaysia, consists of 9 fields with an estimated STOIIP of about 4 BSTB. 6 of the major fields in BDO have been on production for more than 30 years. Average recovery factor to date is about 30%. EOR has been planned as an effort to boost the production as well as prolong the life of the field. A preliminary EOR screening study shows that water-alternating-gas (WAG) is the most amenable EOR process for BDO. A PETRONAS and Shell joint study team was tasked to further extend the screening study conducted in 2005 by developing an EOR Big Picture for BDO. The objective of the study was to quantify the EOR potential in BDO and to develop a holistic areal implementation plan to mature the EOR potential. Scenarios evaluated involved a combination of three gas processes; immiscible hydrocarbon (HC) WAG as well as immiscible and miscible carbon dioxide (CO2) WAG. All reservoirs in BDO were first screened and ranked. Eligible reservoirs were then characterized into a few groups according to fluid, rock type as well as aquifer and gas cap size. Optimized EOR performance was evaluated using full field models as well as smaller scale, detailed prototype models of a few selected reservoirs. The prototype models were developed using field analogue data which were representative of a particular reservoir group. The performance prediction of the remaining reservoirs not modeled was STOIIP scaling of representative dimensionless curves. The HC WAG reservoirs were all immiscible while the potential CO2 WAG was a combination of miscible and immiscible cases. The subsurface EOR evaluation also included an estimation of infill and water flood potential, associated well count, well cost as well as the net gas import required and the total gas handling required. This paper presents the details of the systematic approach used to assess the subsurface EOR potential in the BDO fields.

The Samarang Field is a complex stacked reservoir system, consisting of multiple sand packages separated by thin but continuous shale layers. The general reservoir structure is a faulted anticline. Most reservoirs have an oil rim with associated gas cap and have some natural water influx. During the redevelopment study for Samarang field, an extensive IOR/EOR study was performed, focusing on the largest reservoirs of the field. A full-field simulation model for the M reservoirs (over 25% of the field STOOIP) was built and calibrated with the historical production, pressure, and fluid-contact movement data. Using this model and various cross section models, an extensive investigation was conducted to evaluate the benefit of injecting water and hydrocarbon gas to improve oil recovery in these reservoirs. The results indicated that updip water injection into the gas-cap region of the reservoirs is beneficial in improving oil recovery. Simultaneous updip water and downdip gas injection gave the highest oil recovery, compared to other injection schemes. This Gravity Assisted Simultaneous Water and Gas injection scheme (GASWAG) improved the sweep efficiency of the lower section on the inner part of oil rim with the downward movement of water and at the same time, increases the swept efficiency of the upper section on the outer part of oil rim with upward movement of injected gas. The investigated EOR schemes for M reservoirs could potentially increase the cumulative oil production by 20 MMSTB compared to infill drilling only. This increase represents ∼7% of OIIP. A significant fraction of this oil production can be produced by reactivating existing idle wells during the application of the EOR process. This paper describes the investigation of the gas and water injection to improve oil recovery in the M reservoir layers.

This paper discusses an enhanced oil recovery study of a multilayered mature offshore oil field in Baram Delta. Multiple reservoirs of the field have varying rock and fluid properties.The shallower accumulations contain oil of low API gravity of 19º with very low solution gas-oil ratios, while API gravity increases with depth to 24º in middle formations and 37º in the deepest sands. Upper sands are poorly consolidated with resultant high porosity and permeability. Most of the reservoirs are undersaturated. Initial field development comprised primary depletion with gas lift through vertical and directional wells - mostly dually completed. Field development strategy implemented measures like gravel packing wells to meet the challenges and possible problems during the course of field exploitation. Field performance indicates that the current development strategy and practice may lead to moderate recovery lower than average recovery in Baram Delta fields through primary production. Detailed reservoir characterization has been carried out to capture the reservoir heterogeneity and multiple realizations have been made to understand the major uncertainties of the field. Screening studies for maximizing the recovery from the field suggests gas based EOR techniques may find application. The EOR method of Water Alternating Gas injection (WAG), both immiscible and miscible, is gaining significant interest for improving the oil recovery in offshore fields. The improvement in recovery due to WAG injection is attributed to contact of the upswept zones and modification of residual oil saturations and targeting the attic oil. The advantage of the process is that combination of water and gas injection provides the improved displacement efficiency of gas flooding with improved macroscopic sweep efficiency due to water injection. The result is improvement in recovery compared to separate gas or water injection. Also three phase flow (oil, water and gas) is better in displacing the residual oil compared to two phase flow water and oil or gas and oil. Parameters which are critical for impacting the WAG enhanced oil recovery process are studied thoroughly. These parameters include WAG ratio, injection rates, cycle, well spacing, sweep efficiency and conformance control. WAG is planned for AB, C, D, and EF reservoirs which have low to moderate recovery. The study suggests that improving the well spacing and proper injection volume provides improvement in recovery factor of the order of 8-10%. The paper also discusses the mechanism of the process through mechanistic modeling and laboratory studies for injection water compatibility, rock- fluid interaction, gas mobility control using Nanofluid/Foam which is expected to provide the better sweep and upside potential.

The objective of this paper is to scope the Chemical EOR potential in both GNPOC and PDOC fields in Sudan. From the initial EOR screening, the most amenable EOR processes identified for both GNPOC and PDOC are mainly chemical and thermal EOR. Chemical EOR is the leading EOR process in GNPOC fields while thermal EOR is the leading EOR process in PDOC fields. Chemical EOR evaluation was performed using Eclipse EOR black oil simulator. Simulations were performed on sector models constructed or extracted from full field models which have been conditioned to the current reservoir condition. The chemical input data was referenced mainly from Qing Hai oil field lab data which oil properties are similar to that of Sudan's. The chemical EOR evaluation encompass 3 different types of chemical processes; polymer flooding, surfactant-polymer (SP) flooding and alkaline-surfactant-polymer (ASP) flooding. Chemical EOR can potentially improve field recovery factor between 4-18% depending on the type of chemical EOR process. ASP flooding possess the highest potential with incremental oil recovery over waterflood ranging between 12%-18% followed by SP flooding and polymer flooding. ASP flooding is taken as the reference chemical process in this study as it as it represent the highest chemical potential. The outcome of this study is believe to be helpful to successful planning of Chemical EOR applications in sudan.