An Investigation of Fluid Leakoff Phenomena by Use of a High-Pressure Simulator

This paper describes the results of fluid-loss tests conducted with various hydraulic fracturing fluids through the use of a large-scale, high-temperature, high-pressure simulator (HPS) that has several unique capabilities. Among these capabilities is the ability to perform dynamic fluid-loss experiments over a large surface area under 1,000 psi differential pressure. Nearly all fluid-loss studies previously reported in the literature have described laboratory tests involving small-core plugs with a surface area of approximately 1.7 in.(2).. In contrast, the fluid-loss data collected in the HPS are over a significantly larger surface area, approximately 606 in.(2). Results from the HPS were compared to laboratory data, and significant differences in spurt-loss values were found. Surface texture was also found to be a significant factor in determining the extent of filter cake formation. The paper provides insight into the differences between fluid-loss control mechanisms displayed by Linear polymer solutions and crosslinked gels. Experiments specifically designed to evaluate various hypotheses were performed to determine the significance of external filter cake on fluid-loss control of crosslinked fluids. Conventional fracturing fluids and additives were found to be inefficient in controlling fluid loss to natural fractures in a rock matrix.