Drilling and fracture stimulating horizontal wells in economically marginal fields, such as tight oil reservoirs, is a common practice. Estimating the connectivity between these wells (IWC) is important for the design and management of a field when waterflood recovery is applied. For example, IWC affects the determination of fracture conductivity and length and can help identify favorable locations for infill drilling and optimize injection rates.
Numerical simulators, such as streamline simulation need a geological model to determine IWC. Constructing the geological model, however, may take months. In this paper, we show how an alternative method, developed for and successfully applied in conventional reservoirs to determine IWC, can be modified to estimate tight formation IWC using solely production- and injection-rate fluctuations. The model is based on the Capacitance Model, or CM, and is modified to include a pseudo well (CM-PW).
The CM-PW is tested with various heterogeneous simulation cases and field data. The CM-PW can identify inter-well heterogeneities and differentiate them spatially. We observed that in some cases the CM-PW performs better than streamline simulation results while calculating production allocation factors. The CM-PW detects whether all the injected fluid volume goes to producers. The model accuracy is based on the match to production data and, for all simulation cases, the model accuracy R2 ≥ 0.83. The field application, from a tight oil waterflood in the Bakken Formation, shows that the CM-PW results agree with tracer test results and field reports showing fracture hits between wells. Seismic interpretations also strongly support the CM-PW evaluations.
The IWCs evaluated by the CM-PW during unsteady state flow periods provide key information to make a favorable decision at the early stage of water flooding in tight oil formations. Integrating the connectivity analysis, with tracer tests, seismic, and the geology enabled us to determine the reasons for the connectivity observed, identifying whether injected fluid flows through geological bodies or fractures between an injector-producer pair.