Paper: Pressure and Rate Transients In Commingled, Layered Reservoirs

Because of sedimentation processes over long geological times, hydrocarbon reservoirs are likely to be multilayered. For practical purposes, in the analyses of pressure and rate transient data the reservoirs are commonly treated as a single-layer model. Petroleum engineers better comprehend the models and analyses of single-layer systems than those of multilayer systems. As long as single-layer analysis yields acceptable results, the engineers tend to use single-layer models in analyzing multilayer data. If the multilayer responses are indistinguishable from the single-layer responses, then the single-layer analysis may be applicable to multilayer data. Our research objectives are to study multilayer responses in pressure or rate transient data, estimate individual layer properties, and investigate the results of single-layer analysis on multilayer data. To achieve our objectives. we have revised and improved an analytical model called "Laysim." We used Laysim synthetic data in our study and limited the study to a radial and homogeneous model with isotropic layer properties and a well at center. The model contains layers with no-flow outer boundaries and a slightly compressible fluid with constant viscosity and compressibility. In this research we used log-log diagnostic plots and semilog Horner plots to characterize multilayer pressure and rate transients, and to distinguish between multilayer and single-layer responses in both drawdown and buildup test data. We identified test types and layer properties that are likely to yield multilayer characteristics. We analyzed mu1tila:qer data using a single-layer model, and provided guidelines in interpreting the analysis results. We quantified layer properties by history matching methods using a simple, three-layer model; proposed a two-step procedure for history matching multilayer data; and provided guidelines in matching the data. The history matching methods are simple ways to estimate layer properties without having to do complicated layer testing and interpretation sequentially. We studied relative rate data that are used to allocate the total flow capacity and storativity obtained from a single-layer analysis to individual layer properties. We found their applicability and restrictions.