Near-Well Nonlinear Flow Identified by Various Displacement Well Response Testing

The impact of nonlinear flow phenomena on well response tests is still not completely understood today. With the present paper, a set of 10 well response tests is investigated. The tests were conducted in a fractured Devonian limestone formation close to the western national border of Germany. The test design incorporates a packer as well as different solid cylinders to initiate a series of slug-injection and slug-withdrawal tests by various initial displacements. Nonlinear response characteristics were observed in the course of the tests, which cannot be explained by tubing-controlled flow inside the cased well. The analysis shows that the nonlinear response characteristics are likely to be either formation controlled according to non-Darcian flow developing in a high-conductivity fracture compartment of the tested limestone formation or a consequence of a severe well inefficiency caused by some sort of screen clogging. This inference is obtained from analyzing the data by a nonlinear well response test model, which differentiates between wellbore internal hydraulic head losses and a generalized rate-dependent skin effect accounting for nonlinear flow processes in the vicinity of the well. The potential of identifying near-well nonlinear flow by various displacement well response testing may indicate this methodology to be a valuable complement to modern high-resolution borehole imaging techniques used when characterizing fractured reservoirs and the tightness of fractured reservoir cap rocks.