Evaluating interwell connectivities can provide important information for reservoir management by identifying flow conduits, barriers, and injection imbalances. Injection and production rates contain connectivity information and a number of methods have been proposed to predict connectivity based on this data. The capacitance model (CM) has recently been applied successfully in several real field cases for this purpose. For non-ideal conditions occurring in the field, however, further investigation on the CM is needed to have a better understanding of reservoir heterogeneity and to facilitate more informed comparisons between the CM results and geological information and other available data.
The CM is based on a linear productivity model assuming a pseudo steady state flow regime for slightly compressible fluids. Therefore, we expect within a specific range of fluid and reservoir properties that the results are reliable. The first aim of this work is to determine the range of applicability of the CM before applying it to field data by a sensitivity analysis on accuracy of results. We also briefly address how to extend the model for transient flow regime effects.
Secondly, the CM equation is derived from a productivity model assuming radial flow in the drainage area of each producer and most of the pressure drop will occur within a few feet of the wellbore. In this work, we show that heterogeneities close to the wellbore have more effect on production and the CM parameters than interwell heterogeneities between injector-producer pairs. We demonstrate that the CM is able to assess these near producer heterogeneities. Also, we suggest methods to decouple the effects of well geometry from near well heterogeneities.
Thirdly, we illustrate the application of the CM in heavy oil reservoirs and wormhole assessment. We propose a modification to the CM to make it perform better in real fields when we have producer shut-ins and mini shut-ins or skin changes. The results of one conventional and one heavy oil field cases are analyzed at the end of this work.
Applying earlier methods in real field cases may give misleading connectivity results and inaccurate rate predictions. Adopting the approaches described in this work helps geoscientists and engineers have a better understanding of reservoir heterogeneity and its effects on fluid flow in the reservoir.