Engineering Charts Development for Poroelastic Stress Analysis of Horizontal/Inclined Borehole and Its Application for Breakdown Pressure Prediction

Abstract

Summary This paper develops a set of engineering charts for the time-dependent stress and pore pressure responses at the wellbore surface under ramp-type, finite-length fluid-injection conditions, based on a semianalytical approach with the use of Laplace-Fourier integral transform technique, to facilitate the prediction of borehole breakdown pressure (BDP) for hydraulic fracturing operating practice. The charts are presented in a nondimensionalized form to cover a wide range of borehole/rock parameters, which, in combination with the approximate solution for the impermeable borehole drilling problem for small and large times, can be conveniently utilized to gain a rapid estimation of the lower and upper bounds for the desired BDP. It is found that the generated charts can be significantly affected by both the ramp time and the fluid discharge length but only slightly influenced by the poromechanics parameters of the rock formation. The potential applications of the produced engineering charts in the hydraulic fracturing breakdown analysis are shown in clear detail through an example demonstration. The new BDP model is deemed to be advantageous over the previous models, given that it can more realistically reflect the time-dependent nature of the pore pressure at the borehole surface during fluid injection and also that it has the capability of predicting the essential breakdown time. Comparisons have also been conducted for the BDP between the presently proposed chart-based analytical approach and the available experimental data from the laboratory studies of hydraulic fracturing by fluid injection, and the two results show an overall satisfactory agreement.