Using Well Windows in Full Field Reservoir Simulation

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe windowing technique, introduced by Deimbacher and Heinemann (Ref. 3), allows a time-dependent replacement of grids for a defined area during a simulation run. A window can represent any kind of well with a gridded wellbore and an appropriate grid pattern around the well. Such an approach makes the generally used Peaceman well model superfluous. As the gridded wellbore and the grid blocks around it are small (some cu-ft) the computational stability requires small timesteps and a greater number of Newton-Raphson iterations. It is obvious that this is not feasible if the solution for the fullscale model and the well windows must be performed simultaneously. Therefore in a first step the fully implicit solution for the full-scale model will be calculated but the inner blocks of the windows are solved for the pressure only, without updating the saturations and mole fractions. This solution provides the boundary influx for the windows. In a second step the windows are calculated for the same overall time step with up to 1000 small local steps. This paper presents the general and practical applicability of this method. Windows, constructed by the PEBI (k-PEBI) method, are introduced automatically for all of the wells (vertical, horizontal and slanted).For testing purposes a real case field model was used. It will be shown that the quality of the results obtained for the model calculated with integrated radial grids around the wells and small overall timesteps are equal to those obtained for the same model using the windowing and local timestepping technique.Further it will be shown that solving the window model with large timestep lengths for the first and small lengths for the second solution step results in equal or smaller CPU times and less NR iterations in comparison to the conventional model.

State-of-the-Art of the Windowing Technique

“…Based on the idea that windows with a gridded wellbore and a gridded near wellbore area are excellent ways to model wells in great detail, the technique was extended to create a new well model that can be used on the level of full field reservoir simulation, allowing one to replace the analytical Peaceman approach (13,14) .…”

“…A short summary of the three major steps of the solution procedure is given below; a more detailed description can be found in References (13) and (14).…”

Simulation of anisotropic heterogeneous near-well flow using MPFA methods on flexible grids

“…For active wells, the near-well dynamics can be upscaled utilizing a local fine grid around the well bore [34]. Furthermore, the windowing technique described in [22] is designed to supplement simulations on a global grid with local fine grids. This technique is adaptive in both time and space.…”