A New Method for Determining the Rheology of Crosslinked Fracturing Fluids using Shear History Simulation

Abstract

ABSTRACT A new method which incorporates shear history simulation has been developed for measuring the rheological properties of crosslinked fracturing fluids. This proven method can provide the true rheology of the working fluid which enters the fracture. These data are essential when designing and conducting treatments in low-permeability formations, in order to obtain the desired fracture geometry. Recent research has shown that the rheological properties of crosslinked gels are dependent on the method of preparation and testing. A single formulation of a fluid prepared by two different methods can have resulting viscosity profiles which differ by several hundred percent. The new method of measuring rheology overcomes many of the previous discrepancies resulting from preparation and testing by incorporating a shear history into the procedure. This shear history is similar to the tubular shear history a fluid experiences before it enters a fracture. The shear history apparatus is a capillary viscometer consisting of a series of tubes and additive pumps for the addition of crosslinkers. The length of the tubing as well as the pump rate can be adjusted to match laminar shear rates and shear histories encountered in fracturing treatments. The paper describes a field scale-up model which verified the results of the laboratory tests. Correlation of field data from bottom-hole tubing pressures on several fracture treatments further substantiates the validity of the laboratory apparatus. Results are presented which show that laboratory data can now be used to predict friction pressure exerted by fracturing fluids. Perhaps more important, though, is the insight now available into the true rheology of the fluid that enters the fracture and the development of techniques for controlling this rheology.