A joint gas injection feasibility study by Shell International E&P Inc., PETRONAS and PETRONAS Carigali Sdn. Bhd. has been conducted for the Baram Delta Operation (BDO) fields, offshore Sarawak, Malaysia.The goal of the study was to design a robust pilot project to evaluate and prove the commercial viability of basin wide gas injection.The study consists of several phases, the first of which, and the focus of this paper, is to conduct a screening study to estimate EOR potential and select a gas injection pilot location.The total EOR potential from initial screening was estimated at 200+ MMSTB from six of the nine BDO fields.Building prototype static and dynamic models of the top five ranking EOR targets further refined these opportunities.
To enable screening and ranking of these targets, a spreadsheet based tool was constructed, which allows for rapid re-screening of reservoirs based on starting assumptions.The tool developed, BDO EOR Screening Tool (BEST), is based on several subsurface and surface criteria.The design of the tool allowed for screening of the total EOR potential and to determine the optimal pilot location.The screening required both immiscible and miscible gas injection potential to be estimated.
The top five candidates, based primarily on EOR potential, were modeled and the potential verified using reservoir simulation.The fully miscible injection cases, Baram field as an example, showed similar results to screening estimates; however, the near miscible and immiscible cases at West Lutong and Tukau fields respectively showed a lower potential.Ultimately, the West Lutong M/N reservoir was chosen as the gas flood pilot location for the following reasons:large EOR potential in the M/N and K/L reservoirs,minimum miscibility pressure (MMP) is at or near current reservoir pressure,depositional environment analogous to several other reservoirs in BDO, andconsidered one of three large targets required to implement large scale gas flooding in BDO.
This paper presents the methodology used in the screening of 1,000+ reservoirs and the unique features employed to develop representative prototype models using analogue field data.
Background
The nine offshore Baram Delta fields were discovered in 1969, as shown in Figure 1, and contain an estimated 4,000+ MM stock tank barrels in place ranging in gravity between 20 and 40 API.The productive reservoirs range in depth from 2,000 to 9,000 ftss.Historical production rates have been relatively flat at 80–100,000 barrels of oil per day maintained primarily through infill drilling and new infield development and/or expansion.Most reservoirs are supported by strong aquifer drives with two notable exceptions at Baronia (RV2 reservoir) - currently under waterflood, and several Baram reservoirs currently under depletion.
The stratagraphic framework for the BDO reservoirs is Middle Miocene in age with east-west oriented coastline and a delta progradation southeast to northwest as shown in Figures 2 and 3.The principal reservoirs are cycle V/VI regressive coastal plan and fluvio-marine sandstones.1The depositional environments observed vary where shoreface deposits exhibit higher connectivity and higher areal sweep, such as in the deep Baram and moderately shallow West Lutong reservoirs.
After 30 years of production, several of the large producing reservoirs have achieved high recovery efficiencies (>45%) and have begun producing at high watercuts.Therefore, different enhanced oil recovery techniques are now being considered.Reviewing published data, by the Journal of Petroleum Technology on EOR, suggests that gas flooding is appropriate for commercial EOR projects in the depth and API range of most BDO fields.Shell and PETRONAS agreed in 2003 to conduct a screening study and implement a gas injection pilot to materialize this opportunity, limited to six of the nine existing fields.
