Real-Time Treating Pressure Analysis Aided by New Correlation

Abstract

ABSTRACT A scale-up correlation derived from laboratory experimentation and calibrated with field tubing data provides improved real-time estimates of bottomhole treating pressure (BHTP) during displacement of delayed-crosslink HPG fluids with or without proppant. Current real-time hydraulic fracturing pressure analysis requires knowledge of BHTP throughout treatments. Measurement of this pressure indirectly at the surface through a live annulus or directly by a downhole gauge is not always feasible, practical, or economically justifiable. In these situations, this pressure is estimated by adjusting measured surface treating pressure to downhole conditions. Hydrostatic head is added and friction pressure losses subtracted from surface treating pressure to adjust to downhole conditions. Friction pressure loss estimates typically depend on laboratory, yard test, or field annular flow based, semi-empirical correlations. Correlations developed from data collected by these methods are shown not to be applicable to friction loss predictions for flow of these particular fluids down long vertical tubing strings. Verification of this point is presented in the form of comparison of directly measured values to values predicted by correlations based on these methods presented in this paper and in the literature. A laboratory correlation developed in this paper was found to possess some unique characteristics which lend themselves readily to field calibration with actual tubing friction loss data. Field calibration, combined with a capacity to consider various tubing diameters, flow rates, and gel/proppant concentrations creates a powerful tool for estimating tubing friction pressure loss and hence BHTP when injecting these fluids on a real-time basis.