Effect of Reservoir Porosity and Clay Content on Hydraulic Fracture Height Containment

The technique of hydraulic fracturing is an essential way for reservoir stimulation. Prediction of hydraulic fracture geometry has been a difficult challenge in petroleum engineering. A 3D non-linear model is established for simulating hydraulic fracturing processes based on the ABAQUS code. The fluid-solid coupling equations consist of rock stress equilibrium, porous fluid mass conservation, Darcy’s law and effective stress principle. The differential equations are discretized in finite element form and solved. The cohesive elements based on damage mechanics are adopted to model the fracture initiation and propagation. A typical hydraulic fracturing process of a horizontal well in Daqing Oilfield, China is simulated with this model. Variation of proppant concentration during the fracturing procedure is taken into account by the user-subroutine we developed. The bottomhole pressure evolution obtained from the simulation is consistent with the field-measured data. Thus the model is verified. For vertical fracture, the effect of formation porosity and clay content on fracture height containment is investigated and discussed. The rock properties are connected to porosity and clay content by a set of formulae. The results show that larger porosity and clay content could confine the fracture height. As the porosity of the pay layer increases, the permeability increases while the elastic modulus decreases. Since the fracturing fluid leaks off into the reservoir more easily for larger porosity formations, the fracture height decreases and the bottomhole pressure drops. With the increase of the clay content of barrier layers, the elastic modulus decreases and the tensile strength of rock material increases. And the fracture height will decrease as the material is more difficult to be damaged for larger clay content formations. Our work can provide a new understanding of fracture height containment and could benefit the design and practice of hydraulic fracture treatment.