ABSTRACT:

Hydraulic fracturing is an important stimulation treatment to create an enhanced geothermal system. Accurate interpretation of the breakdown pressure (the critical pressure at which “breakdown” takes place in hydraulic fracturing) can assist engineers to better performing hydraulic fracture treatment designs. The breakdown pressure is known to exhibit a dependence on wellbore size, pressurization rate, fluid viscosity, fluid infiltration, and fluid compressibility. Determination of breakdown pressure has been the subject of intense study for several decades. However, little attention has been drawn to effect of non-linear fluid compressibility on breakdown pressure. Here, we modified the Ito’s tensile failure criterion by replacing the Terzaghi effective stress with a general effective stress and developed a breakdown criterion that accounts for fluid type and state. The present model gives good agreement with experimental data. Sensitivity studies are conducted to investigate the influences of fluid compressibility, fluid viscosity, and pressurization rate on the breakdown pressure. It indicates that 1) the non-linear compressibility effect inhibits the propagation of pore pressure perturbation, and 2) for inviscid fluid, the breakdown pressure is a constant, which corresponds to the lower limit of the breakdown pressure. The proposed model can provide some theoretical support in hydraulic fracturing treatment design.

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