Successful fracture treatments that utilize crosslinked fluids are dependent on the fluid maintaining viscosity at down-hole conditions. Pre-job testing of the crosslinked fluids is a critical step in knowing how the fluid will perform during the treatment. Using proper testing guidelines and contingencies in place, the service company can provide operators useable, predictable fracturing fluid test data. Without such guidelines, extraneous testing, unusable data, and job delays can result.
Crosslinked fracturing fluids are tested using a rotational viscometer designed for testing at elevated temperatures and pressures under a constant shear environment. Such viscometers are among the most economical and readily available approximations to the down-hole environment experienced by fracturing fluids. By setting the rotational viscometer to approximated job conditions, and utilizing treatment-specific water and chemicals, it is possible to produce data that predicts the rheological properties a crosslinked fluid will exhibit during fracture treatment.
Before rheological testing begins, the operator and service company must agree upon parameters that are acceptable for the testing procedure. While the ISO-13503-1 document outlines standard practices for measuring the viscous properties of completion fluids, there are job-specific factors that are not addressed in this document. First, the operator may want to specify the exact rheological requirements expected in order to categorize fluid as effective for the treatment. Next, the temperature and shear rate settings must be agreed upon to ensure the viscometer is run at the most probable down-hole conditions for the given job. Finally, the operator or service company may pre-determine the range of chemical additive loadings for several of the crosslinked fluid components (i.e., an optimization path). This paper will outline areas the of a crosslinked fluid test that need to be clearly defined prior to testing, and will show the potential time and financial costs associated with the lack of concise guidelines.