Material balance computations provide a mechanism for estimating the volume of fluids in place underground. Frequently the material balance is applied without using exhaustive static data from geophysical, geological and petrophysical analyses that would provide an independent estimate for fluid volumes in place. Workstations offer a possibility to integrate data from many sources and enable highly detailed visualizations of delineations of reservoir limits, correlations of geological features among wells, potential barriers to flow, and reservoir heterogeneity. The reservoir model derived from the workstation environment contains sufficient detail to discourage the conventional global material balance approach as too simplistic. Instead, partitioning the reservoir into compartments, or portions of the reservoir with similar fluid flow characteristics and a common recovery mechanism, offers a means to incorporate the volumetric estimates from static data into material balance equations, thus enabling the use of these equations for additional purposes.
Fox, et al. introduced the compartmentalized single phase material balance as a means for characterizing intercompartment communication and effective compartment volumes and for interpreting pressure transient well tests and formation test pressures in heavily faulted formations. This work extends the concept to multiphase and multiwell cases and for vertical compartmentalization in addition to horizontal.
The objectives of the compartmentalized material balance introduced in this work are to validate compartment volumes, fluid PVT behavior, rock compressibility, and production data, and to quantify and characterize flux between compartments. This paper details the computations used and some of the theory behind them. Then practical applications for this type of model are described.
The integration of geophysical, geological, and petrophysical interpretations enables delineation and quantification of the volumes in which reservoir fluids (gas, oil and water) are stored underground. In absence of significant formation subsidence, the total bulk reservoir volume is fixed while reservoir fluids are produced from wells. As fluids are produced, the remaining fluids in the reservoir must expand continually to fill the fixed volume.