Quantifying Nonuniform Aquifer Strength at Individual Wells

Abstract

Summary In waterdrive reservoirs, the aquifer influx experienced by each well is a function of reservoir heterogeneity and operating variables. Solving multiwell field problems necessitates estimating this variable influx. Yet no simple approach allows us to discriminate this differential influx commensurate with well characteristics. Direct application of analytical aquifer models, being applicable to the entire reservoir, is nondiscriminating, particularly when inferring individual well influx is concerned. In contrast, numerical models allow flexibility with the use of pore-volume multipliers in the aquifer cells; however, actual experience shows that approach to be less than satisfactory. This paper outlines a method for modeling differential aquifer influx received at each well; the combined use of capacitanceresistance model (CRM) and analytic aquifer model underpin the proposed approach. This study presents an unsteady-state aquifer formulation, without the need for dimensionless aquifer-function tables. The formulation allows treatment of both unsteady-state and pseudosteady-state flow behaviors with the simplified form of the van Everdingen and Hurst (vEH) formulation. This aquifer model is then coupled with CRM on an individual-well basis. In other words, because each well is attached to a different aquifer model, appropriate water influx can occur commensurate with rock properties, fluid withdrawal rate, aquifer size, etc. A synthetic example verifies and a field example validates the proposed method.