Friction & Sliding on Fracture Surfaces: A New Mechanism for Increasing Drilling Fluid Leakage in Deep Fractured Reservoirs

Because repetitive leakage in greater volume often occurs in deep fractured reservoirs after the failure of initial plugging, fracture plugging simulation before and after the sliding with friction happens on fracture surfaces (referred to as friction & sliding on fracture surfaces) was designed and carried out. Supported by the friction & sliding experiments of rock plates and blocks in drilling fluid environment, rock mechanics parameter test based on micron indentation and the three-dimensional surface scanning, the inducing effect of drilling fluid intrusion on the friction & sliding on fracture surfaces was analyzed, and the influence on drilling fluid leakage in fractured reservoirs brought by friction & sliding on fracture surfaces was explored. Experiments showed that when the drilling fluid invaded natural fractures, both oil-base and water-base drilling fluids could decrease the friction factors of fractured rock surfaces, and the oil-base drilling fluid could brought a stronger effect, which would induce friction & sliding on fracture surfaces to form dislocated fractures, providing channels and space for the aggravation of drilling fluid leakage. Also, friction & sliding on fracture surfaces can increase the permeability of fractures, resulting in a decrease in the plugging capacity of drilling fluid and increasing drilling fluid leakage. Moreover, fracture surfaces were smoother after friction & sliding, which may further intensify the degree of dislocation. With the huge increase in the length and width of fractures, the leakage of drilling fluid was exacerbated. The research results showed that friction & sliding on fracture surfaces was one of the reasons for the exacerbation of drilling fluid leakage in deep fractured reservoirs. Drilling fluid leakage in deep fractured reservoirs could be controlled by increasing the friction factors of natural fracture surfaces and effectively controlling the friction & sliding on fracture surfaces.