We investigated the application and usefulness of the producer-based representation of the capacitance resistance model (CRM) to characterize single and multiwell undersaturated oil reservoirs during primary recovery.

The CRM is a physics-based, data-driven method that has been amply used to model reservoirs under different recovery stages, particularly during flooding processes. However, there have been very few applications to primary recovery. The previous work on primary recovery used the rate and bottomhole pressure (BHP) data to calculate the time constant or storage capacity, and the productivity index (PI) associated with each production well. Here, we incorporate popular productivity models in CRM, making the results comparable with those from pressure transient analysis (PTA) or rate transient analysis (RTA). We also investigate various topics that have not been discussed or that deserve a further explanation to include CRM in the reservoir engineering toolbox. These comprise constant and variable rate wells, transient flow, well location, well geometry, anisotropy, and different types of reservoir heterogeneity. CRM is systematically compared and validated against analytical and numerical models of single and multiwell reservoirs. We also use it to characterize flow in a real oil reservoir .

Our results demonstrate that CRM can provide important parameters for reservoir characterization using BHP and rate data acquired from routine production operations, that is, without the need to shut in wells or perform dedicated tests. It yields reasonable estimates of flow resistance properties that depend on reservoir geology, petrophysics, and well condition. It can also be applied during successive time intervals to assess changes in well-reservoir properties, such as drainage radius or the PI, an indication of well damage. Most importantly, we show that for several well-reservoir cases with multiple complexities, CRM can accurately capture the reservoir size, or the drainage pore volume (PV) associated with each well in developed fields, which enables the calculation of average pressure and helps assess interwell communication and opportunities for infill drilling.

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