The Nonhomogeneous Flow Character of a Delayed Crosslinked Gel

ABSTRACT Experiments were done using modified Model 50C Fann viscometry and tubular flow tests to study the nonhomogeneous flow character of a delayed cross- linked fracturing fluid. Previous testing showed that a delayed crosslinked fracturing fluid can exhibit two distinct forms of nonhomogeneous flow when tested on the Model 50C Fann viscometer. At low shear stresses, the fluid exhibited apparent slip flow with low viscosities, but when the stress was increased to a critical value, the gel broke up forming a dispersed fluid with a much higher viscosity. However, in the dispersed form, nonhomogeneous flow was still evident. Testing described in this work found that when this fluid is crosslinked at very low shear energies on the Fann viscometer, the resulting gel still exhibits apparent slip flow, but with very high viscosities. In this case, high stresses are required to break up the gel. Flow visualization tests indicate that the stress buildup during gel breakup results from a flocculation process and secondary flows as well as destruction of the low-viscosity slip layer. When tested in a tubular-flow loop, this gel did not exhibit comparable stress buildup behavior. However, retesting of flow-loop generated gels on the Fann viscometer showed that flow-loop data corresponded most closely to the low viscosities observed on the Fann viscome-ter when the gel was in apparent slip-flow. Thus, this gel may slip when tested in tubular flow and perhaps when flowing in fractures.