Study on In-Situ Stress Evolution and Its Impact on Infill Well Fractures Propagation- A Case Study from China

Abstract

Hydraulic fracturing of horizontal wells is an effective development mode for low-permeability reservoirs, while new drilling can enhance reservoir recovery. The drilling, fracturing, and production processes all induce changes in reservoir stress, affecting the infill wells’ fracture design. Adoption of finite element-based discontinuous discrete fracture numerical method. The extension of wellbore and fracture is described by dynamic mesh technology during drilling and fracturing, and the discontinuous discrete fracture model can be computed by using a conventional finite element mesh, which can be perfectly matched with the discrete fracture model, so as to realize the integrated numerical simulation of drilling-fracturing-production. Use the construction of infill wells in low-permeability reservoirs in Area 8 as an example, the integrated simulation of drilling-fracturing-production is carried out for the wells to be constructed in the encrypted well area, and the maximization of the exploitation economy of the well area guides the optimization of the infill wells’ fracturing. The simulation results show that the long-term production process of the old well reduces the formation pressure and ground stress in the encrypted well area, and the direction of the maximum horizontal principal stress is deflected. Considering the influence of the old well production, the drilling fluid density during the drilling of the encrypted well can no longer be designed using the original formation pressure profile. With the drilling fluid column pressure not greater than the minimum horizontal principal stress at this stage, the direction of maximum horizontal principal stress around the encrypted well is further deflected after the wellbore is drilled open, causing the initial expansion direction of the fracture to be deflected along the wellbore; injecting water to boost the pressure of the old well prior to the fracturing of the encrypted well can improve the fracturing effect of the encrypted well. The established numerical method can realize the simulation of reservoir stress evolution in the whole process of drilling-fracturing-production and the integrated numerical simulation of fracturing-production, which can optimize the design of fracturing in infill wells and improve the single-well production.