Many gas-condensate wells show a significant decrease in productivity once the pressure falls below the dew point pressure. A widely accepted cause of this decrease in productivity index is the decrease in the gas relative permeability due to a buildup of condensate in the near wellbore region. Predictions of well inflow performance require accurate models for the gas relative permeability. Since these relative permeabilities depend on fluid composition and pressure as well as on condensate and water saturations, a model is essential for both interpretation of laboratory data and for predictive field simulations as illustrated in this article.S lr ϭmin ͩ S l ,S lr high ϩ S lr low ϪS lr high 1ϩT l ͑ N T l ͒ l ͪ . ͑4͒

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA fully implicit equation-of-state (EOS) compositional simulator for large scale reservoir simulation is presented. The simulator uses a multiblock, domain decomposition approach; that is, the reservoir is divided into non-overlapping subdomains that are solved locally in parallel (inner iteration). The subdomain grids are defined independently of each other and their connections are attained through a global interface problem (outer iteration) formulated in terms of appropriate equations that guarantee continuity of total component fluxes. Parallel, iterative techniques are employed to solve the resulting nonlinear equations. The model formulation has been successfully tested for a dry gas cycling process on a single fault block. The numerical results show that the simulator and fluid-related calculations can be conducted efficiently and robustly. Promising results have been obtained using the proposed multiblock approach for nonmatching grids between fault blocks for two-phase flow problems.This work is presented in two parts. In Part I we outline the mathematical formulation and discuss numerical solution techniques, while in Part II we address framework and multiprocessing issues.

ReservoirsThe University of Texas at Austin scheme for computing the gas and condensate relative permeabilities as a finction of the capillary trapping model and with only data at low trapping number (high IFT) as input and have found good agreement with the experimental data in the literature. We then used this model and typical parameters for gas condensates in a compositional simulation study of a single well to better understand the PI behavior of the well and the significance of the condensate buildup.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA fully implicit parallel equation-of-state (EOS) compositional simulator for large-scale reservoir simulation is presented. This simulator is developed under the framework named IPARS (Integrated Parallel Accurate Reservoir Simulator) and is constructed using a Newton-type formulation. The Peng-Robinson EOS is used for the hydrocarbon phase behavior calculations. The linear solvers from the PETSc package (Portable Extensible Toolkit for Scientific Computation) are used for the solution of the underlying linear equations. The framework provides input/output, table lookups, Fortran array memory allocation, domain decomposition, and message passing between processors for updating physical properties in mass-balance equations in overlapping regions. PETSc handles communications between processors needed for the linear solver.Many test runs were performed with up to four million gridblocks for a dry-gas injection process on an IBM SP machine and half a million gridblocks on a cluster of 16 PCs. Results indicate that the scalability of the simulator is very good. The linear solver takes around half of the total computational time for homogeneous reservoirs. For layered heterogeneous reservoirs, the linear solver took a larger fraction of the total computational time as the permeability contrast increased. The time for the communication between processors for updating the flow equations is insignificant.The PC cluster is roughly a factor of two slower than the SP for parallel runs, which is very encouraging. This factor is strongly related to the hardware configuration of the computers, which is detailed in the paper.