| For the oil and gas wells that have been put into production after fracturing. it is necessary to take the secondary reorientation fracturing to achieve the effective exploitation of the rest of oil and gas and the improvement of per well production and ultimate recovery, since the whole of oil and gas controlled by the initial fracture have been almost extracted. Aiming at the fractured vertical gas well, this paper studies systematically the stress change disciplinarian nearby the wellbore and the initial fracture, the mechanism of new fracture reorientation and the extension trajectory of new fracture. The main achievements and understands are as follows:(1) Based on elasticity theory, the mathematical model of the induced stress caused by the initial artificial fracture is established and solved, and then the factors affecting this induced stress are analyzed, which shows that with the increasement of the net pressure imposed on the fracture surface and the fracture height, the artificial fracture induced stress and the induced stress difference increase; as Poisson’s ratio increases, the artificial fracture induced stress increases. but the induced stress difference decreases.(2) Integrating fluid mechanics in porous medium and rock mechanics, a flow-solid coupling mathematical model is abstractly set up. As solving, the method of finite difference is adopted for filtration model taking permeability orthotropy into consideration, while the finite element method (FEM) is taken for rock-change model. And then the explicit alternate way is used to realize the overall solution. So the quantitative analysis and the simulation of this induced stress field are realized.(3) According to the established flow-solid coupling calculation model, the factors affecting the induced stress field by gas production are analyzed, which shows that the longer production time, smaller bottom hole flowing pressure and the stronger permeability orthotropy are conducive to the formation of greater stress-induced difference around gas well, so the area where the stress field redirects gets lager. The impacts of primary fracture length. Poisson’s ratio and elasticity modulus on production-induced stress are relatively small. And the increasement of Poisson’s ratio and elastic modulus are not beneficial to the stress redirection, while primary fracture length mainly affects the stress redirection of the area away from wellbore in the initial fracture direction.(4) The fracture initiation criterion of maximum circumferential tensile stress is adopted to analyze the new fracture extending track. And then the analysis of the factors affecting new fracture extending trajectory are conducted, which shows that the production time, bottom hole flowing pressure, permeability orthotropy and the original horizontal principal stress difference are the main factors. And the longer production time, smaller bottom hole flowing pressure, stronger permeability orthotropy and the greater original horizontal principal stress difference are conducive to forming a new fracture that has a greater reorientation-distance to communicate the unspent area of reservoir as possible.(5) Based on the theory derived, the calculation procedures of the present stress field and new fracture extending track are worked out in the VB6.0software platform, through which the relevant quantitative analysis and simulation can be done.This study provides certain theoretical basis for the secondary fracturing optimization design and some guidance for the field treatment to improve its technological and economic feasibility, which is of great significance for integrated management and for steady production and stimulation in maturing oil and gas fields. |
