Development and application of a local grid refinement technique for accurate representation of cavity-completed wells in reservoir simulators.

摘要

A three dimensional, single- and two-phase fluid flow model of cavity-completed wells is presented. Cavity-completed wells are approximated as a collection of fine rectangular cells, and the residual equation is utilized to determine the flow into the cavity. The constructed fine grid lines are terminated at the coarse/fine grid interfaces by implementing a newly developed local grid refinement technique. The adopted approach is significantly different from the current simulation applications in which the cavity-completed wells are incorporated into computations by assigning large wellbore radii and/or large negative skins to conventional well equations.; During the cavity completion process in coal seams, it is hypothesized that fracture networks are generated in certain directions around the cavity. These fractures are generally included into a simulation study by modifying the permeability values around the wellbore. The presented model provides not only a precise approximation to the physical structure of the cavity, but also a good representation of the altered permeabilities around the cavity using the fine grid cells that are already in place. In addition, local characteristics within the immediate vicinity of the cavity such as pressure and saturation distributions may be captured accurately with the help of local grid refinement without using excessive number of fine grid cells. The model is also capable of providing an accurate very early-time flow response of a cavity which may be critical for well test analysis of cavity completions.; The effects of cavity dimensions and generated fracture networks on the flow performance of the cavity are investigated for various reservoir systems. Additionally, the performances of cavity completions and hydraulic fracturing in coal seams are compared with each other. The model presented is capable of providing quantitative and qualitative information to the completion engineer who is facing critical decisions for the cavity completion and hydraulic fracturing practice in coalbed field development projects.