Interwell connectivity, an important element in reservoir characterization, especially for secondary recovery such as waterflooding, is essential when making decisions on well patterns, infill wells, and injection rates for oil recovery optimization. An existing technique uses multivariate linear regression analysis of flow rates in a waterflood to infer interwell connectivity. Advantages of this technique include a simplified one-step calculation and the availability of production data. A capacitance model was introduced as an extension of the technique to account for shut-in periods and changes in bottomhole pressures in the producers; however, this approach is based on trial and error and requires subjective judgment.
This paper presents an alternative analytical approach based on analytic concepts, providing an in-depth understanding of the technique and relationships between interwell connectivity coefficients and other reservoir parameters. The analytical approach uses a mathematical model for bottomhole pressure responses of injectors and producers in a waterflood system. The model is based on a solution for fully penetrating vertical wells in a closed rectangular reservoir with an assumption of steady-state flow. This model is then used to calculate relative interwell permeabilities, which represent the connectivity levels of signal response well pairs.
Different synthetic reservoir models were analyzed, including homogeneous, anisotropic reservoirs, and reservoirs with high-permeability channels and transmissibility barriers. Comparisons with results obtained from previous studies of production data and bottomhole pressure data are presented.
The main findings of this study are: (a) the mathematical model performs well with interwell connectivity coefficients calculated from flow rate data to quantify reservoir parameters; (b) the proposed approach provides a better understanding of interwell connectivity determination from flow rate data;and (c) the results for relative interwell permeability from flow rate data are similar to those obtained from previous studies of bottomhole pressure data.