Infill Wells Placement in High Water-Cut Mature Carbonate Field with Simulation Opportunity Index Method

Abstract

Abstract Despite intelligent method such as numerical simulation model has been used, identifying areas or zones that still holding high potential of production still becomes the most challenging aspect in the development of mature carbonate oil field with high water-cut; especially coupled with the lack of required important data to generate such appropriate model. A practical method to explore the sweet-spot areas within the field is then introduced, hereinafter called "Simulation Opportunity Index" (SOI) based on techniques already established in the industry. SOI is an integration of three (3) independent components whereas each of them is normalized to produce indexes that represent reservoir-permeability thickness, movable oil and reservoir pressure from a historically-matched dynamic model. The method utilizes the historically-matched simulation model in which the water saturation from the dynamic model is calibrated with the recent acquired cased-hole logging saturation log to improve the confidence level. The cased-hole logging saturation log results are treated as the only ground truth of the current saturation within the reservoir thus it plays important role to reduce the model uncertainty and to simplify the workflow in efficiently short time. The SOI method is hence used as an invaluable tool to spot areas for further development such as infill wells. The workflow to produce the potential areas within the reservoirs is discussed in this paper including comparison to see infill wells performance by using both conventional and SOI approaches. Notwithstanding lesser producible oil reserves due to denser-placed infill wells over time and high water-cut of the field >95%, the method after implementation in numerical simulation is capable to screen-out a number of sweet-spot areas for infill wells placement in the largest mature oil field of RH PetroGas (Basin) Ltd concession in Salawati basin, onshore West Papua, which can be ranked thereupon for execution after sensitivities and economics analysis. The infill wells are still the most technically-favourable development scheme to hold oil production decline about 6%/year in the field. Thus, it is essential to place the infill wells within the most optimum locations that would yield maximum sweep efficiency, acceleration of the expected recovery or incremental increase of the Estimated Ultimate Recovery (EUR) from such heterogeneous reservoirs. The application of SOI methodology in numerical model is helpful to practically identify areas or zones with high oil potential due to non-uniformity volumetric sweeping efficiency in carbonate reservoirs in relation to their tremendous heterogeneity, variable wettability and dual pore network.