Optimization Strategy for Producing a Low Permeability Non-Associated Gas Reservoir

Abstract

Abstract Planning a well to drain low permeability non associated gas reservoirs is challenging especially when, production from existing wells from other reservoirs has started declining and the need to sustain gas volume contract requirement becomes imperative. The fundamental expectation is to demonstrate that product volumes add up to an acceptable stipulated economic standard to approve or endorse project execution. Commitment to Flow Assurance management (surface and subsurface) is also paramount while optimizing all other objective functions. This paper reviews the optimization strategy of a non-associated gas reservoir taking into consideration the dynamics of operational needs and then carrying out the value chain optimization of products to provide a profitable solution. An Inflow Performance Relation (IPR) modelled from a Drill stem Test (DST) data was used to estimate productivity from an Experimental Design (ED) methodology involving varied reservoir thickness, reservoir permeability and Gas Initially In Place volumes. Vertical lift performance was designed to ensure that the overall well flow honored darcy flow of analogue gas reservoirs that are currently producing in experimented data space. An Integrated Production model was developed out of reservoir model, well model and surface flow model to mimic productivity in real time conditions and serve as the basis for reserves forecasting, project life and product volume forecasting. Additionally, the model enables investigation of surface and subsurface Flow Assurance. Results from the forecasts were used to update reserves, optimize wells’ drilling plan, improve expected products volume records, and adequately plan the flow assurance of the wells. One well per reservoir, adjudged from economics as being optimal, was planned on three reservoirs and the economics indicator (Discounted Profitability Index – DPI) for the individual projects were (5.0, 2.9 and 1.7) uniquely proven worthwhile for any standard investment. A total gain of about 80 MMSCFD and 4,100 BPD of condensate was achieved proving up about 250 BCF of gas with associated condensate reserves of 7 MMSTB.