A fully coupled three-dimensional hydraulic fracture model to investigate the impact of formation rock mechanical properties and operational parameters on hydraulic fracture opening using cohesive elements method

摘要

Hydraulic fracturing operation success is critically dependent on pre-operation fracture geometry analysis. Meantime, hydraulic fracture opening determination is crucial because it deals with maintaining sufficient aperture and efficient communication pathways to accomplish proppant placement and avoid screen-outs or proppant bridging. It is well understood that, to efficiently estimate the hydraulic fracture opening, a thorough understanding of the impact of rock mechanical properties as well as operational parameters such as injection fluid viscosity and leak-off are essential. In this study, a three-dimensionalmodel has been developed for parametric study of fracture stiffness, formation elastic modulus, formation Poisson's ratio, tensile strength of the rock, fracturing fluid viscosity and leak-off, and their influences on hydraulic fracture opening. Cohesive elements with traction-separation law have been applied to simulate the fracturing process in a fluid-solid coupling model. The maximum nominal stress criterion has been selected for initiation of damage in the cohesive elements. The results revealed that any change in influential rock mechanical properties as well as operational parameters would significantly lead to increasing or decreasing the hydraulic fracture opening. It was observed from the controllable HF parameters including fracturing fluid viscosity and leak-off, by increasing fracturing fluid viscosity from 10(-3) to 10 Pa.s, fracture width has been moderately increased from 8.83 to 13.3mm; on the other hand, by reducing leak-off coefficient as a polymer-dependent HF parameter from 5 x 10(-9) to 5 x 10(-11) m/kPa.s, fracture width has been gradually risen from 7.27 to 11.52 mm. In addition, all the uncontrollable rock mechanical parameters such as fracture stiffness, Young's modulus, Poisson's ratio, and tensile strength have steeply increased or decreased the hydraulic fracture opening and consequently, all of their analysis will be discussed in detail in this research. The results from this study can be applied to hydraulic fracturing jobs in different conditions of fracture stiffness, formation elastic modulus, formation Poisson's ratio, tensile strength of the rock, fracturing fluid viscosity, and leak-off.