Research On The Refracturing Stress Field Based On Damage Theory

The refracturing technology is the main treatment to increase production and injection, which has been widely applied in the low permeability oil-gas field development. It has made important contribution to keeping production stable. The previous research of refracturing stress re-orientation obtained total stress field before refracturing based on the different stress field linear superimposition. The previous research only focuses on the initiation and extension of single crack and ignores the damage of rock mass in effective action sphere. Damage characteristics and micro cracks forming process of hydraulic fracture rock are studied based on damage mechanics in this paper. The study of stress distribution around wellbore rock is carried on based on damage mechanics. The research method of the description of hydraulic fracturing rock mass destruction and micro crack formation is built up, and the new study and calculation method is provided for making up for a deficiency of fracture mechanics research hydraulic fracturing. Main work and research results are as follows:Systematic research on refracturing in-situ stress field of rock around borehole has been done based on damage mechanics theory in this paper. Double medium rock seepage effects is considered in this paper, wellbore area is divided into breach zone, the damage zone and the elastic zone, the model and calculation of rock stress distribution breach radius and damage radius are built up based on damage theory. Calculation model of total stress before refracturing has been established using principle of virtual work in damage zone. Calculation model of stress before refracturing has been established based on linear superposition principle in the elastic range, which lays a foundation for hydraulic fracturing rock damage mechanics model and nonlinear damage evolution.In this paper hydraulic fracturing rock damage and micro cracks formation are studied by innovative use of damage mechanics theory, a new research direction is opened up for hydraulic fracturing rock damage characteristic and fracture distribution status. The more mature and reliable scientific evidence is provided for more profoundly understanding the rock fracture mechanism in the hydraulic fracturing process, the vigorous theoretical guidance and technical support are provided for further improving hydraulic fracturing design, which has great academic value and practical significance.