| Popis: |
ABSTRACT: Refracturing is an effective way to drain the unstimulated rock through diversion treatment. The refrac geometry is determined by the reorientation and change in the magnitude of the in-situ stress. However, the comprehensive impact of primary fracturing, water injection and oil production in well group on the stress redistribution has not been well understood. A three-dimensional heterogeneous geomechanical model coupled with unconventional fracturing and reservoir simulation was established. Following the primary hydraulic fracturing and water injecting according to the pumping and injection schedule of an inverted nine-spot well group, an automatic gridding algorithm was run. In addition, history match and 10-year production prediction were conducted through reservoir simulation. A 3D geomechanical finite element solver was utilized to compute the spatial and temporal change in the in-situ stress and deformation during fracture propagation and reservoir depletion, providing updated stress profiles. Refrac simulation scenarios were run after production of 1 year, 3 years, 5 years and 9 years to identify the most opportune time to refrac the well group. Results indicate that the impact of water injection on stress is consistent with hydraulic fracturing while opposite to that of the reservoir depletion. The magnitude of horizontal principal stresses increases around the injection well, while the stress contrast decreases during the water injection. Hydraulic fracturing induces tensional and compressional stress perturbation around the producing well in the vicinity of fracture tips and fracture walls while the stress is released as the well produces. In addition, the magnitude of stress variation in the well group increases with the depletion at the beginning, followed by a decrease. It is beneficial to refrac the well group 3 years after the first treatment. The impact of water injection, primary hydraulic fracturing and well depletion on the variation of in-situ stress was clarified through an integrated modeling in this study, providing insights for the design and evaluation of refracturing treatments to enhance the field development of the low permeable reservoirs. |
