Optimization of the horizontal-well multiple hydraulic fracturing operation in a low-permeability carbonate reservoir using fully coupled XFEM model

摘要

Pre-analysis of the geometry and deviation of multiple hydraulically induced fractures is a decisive factor in the successful multiple hydraulic fracturing operations. Besides, fracture spacing should be optimal for obtaining desired results such as maintaining sufficient aperture for proppant placement, avoiding screen-outs and also preventing fracture closure or crossing multiple fractures. In fact, the final geometry and deviation of multiple hydraulic fractures are dramatically influenced by the interaction of multiple hydraulic fractures on each other known as stress shadow effect which is caused by fracture spacing and pore pressure change. Predicting the geometry and deviation of multiple hydraulic fractures is a challenging part of conducing this technology in Ilam reservoir due to low matrix permeability and naturally fractured nature of the reservoir. Accordingly, a fully coupled stress-diffusion XFEM model for initiation and propagation of multiple hydraulic fractures with five injection zones was prepared to optimize the effect of fracture spacing and pore pressure change on the multiple hydraulic fractures' deviation and geometry. Additionally, the XFEM model was verified by three approaches including field data, Stress Intensity Factor and KGD zero toughness solution wherein a very good agreement with negligible error was obtained for SIF, field data and KGD M-vertex solution. However, this study has confirmed that both pore pressure and stress shadows contribute to change the fracture geometry and its deviation significantly in Ilam reservoir. Also, increasing pore pressure between fractures, may affect the fracture geometry to be tighter in width and shorter in length. In addition, considering optimized fracture spacing about 75 m resulted in creation of very smooth, uniform and deeper multiple hydraulic fractures; so, there will be no closed fractures in DPH-02 horizontal wellbore and the possibility of crossing the furthest fracture by the second fracture significantly reduced when the fracture spacing was higher than 5 m.