Perforation Friction Pressure of Fracturing Fluid Slurries

Abstract

Abstract Even though pressure drop across perforations for clean fracturing fluids can generally be accurately predicted, it is not well understood for fracturing slurries. In this paper, two wellbore models-one transparent and one high pressure-were used to study the perforation friction pressure behavior of sand laden fluids. The transparent model constructed with cast acrylic allowed visual observation of fluid exchange in the "rat-hole" and flow patterns of the slurries in the wellbore and through the perforations. Critical velocity at which sand begins to screenout at the perforations was also determined. Tests were performed in the high pressure model varying gel concentration, sand concentration, proppant size, and perforation diameter to gather pressure drop data. The effect of the ratio of perforation diameter to the average proppant size on the sand screenout tendency at the perforation was also investigated. A correlation to predict the change of perforation coefficient due to proppant erosion was developed from the laboratory data. This paper presents a field procedure to better estimate the change of perforation coefficient during proppant stages for calculating the change of perforation friction. Incorporating this change of perforation pressure drop during proppant stages in the real-time bottomhole treating pressure calculation will enhance interpretation of the treatment analysis. Introduction During a fracturing treatment, fluid containing proppant is pumped down a tubular string, through perforations, and into a fracture. Without a bottomhole tool or reference string, the bottomhole treating pressure is calculated from the following equation. (1) where: BHTP = Bottomhole Treating Pressure (psi) Pw = Wellhead pressure (psi) Ph = Hydrostatic pressure (psi) Pf = Fluid friction pressure in tubular goods (psi) Ppf = Friction loss across the perforations (psi) Using an on-site computer system to perform real-time fracturing pressure analysis to predict fracture propagation requires reliable estimates of the BHTP. P. 479^