Method and system for determining fluid pressures in wellbores and

Abstract

Friction pressure losses are obtained for non-Newtonian or generalized Newtonian fluids being pumped through conduits at high flow rates, such as in hydraulic fracturing of subterranean formations, by measuring friction pressure losses in a pipe viscometer under laminar flow conditions. The pipe viscometer includes a pump which supplies fluid to a continuous loop having three pipe sections of different diameter for measuring pressure drop at different flow velocities. Sets of data points of generalized shear stress and shear rate are measured for determining the consistency index (K') and the Power Law or flow behavior index (n'). The generalized Reynolds number of the fluid being pumped is determined using the values of consistency index and flow behavior index and this Reynolds number is maintained in a second pipe viscometer section arranged in parallel with the laminar flow loop by pumping the same fluid wherein the second pipe viscometer section has the same roughness as the conduit through which friction pressure loss is to be determined. The Fanning friction factor (f) is determined for the pipe viscometer section from known values of friction pressure drop over a predetermined length of the pipe viscometer section at a known flow velocity, known fluid density and known hydraulic radius of the pipe viscometer section. The actual pressure drop over a predetermined length of conduit is determined using the calculated value of friction factor (f) and measured values of fluid density, flow velocity and conduit dimensions.