Study On Fluid - Solid Coupling Seepage Mechanism Of Fractures

The fractured reservoirs generally is deeply buried, and the safe density window is narrow. The wellbore pressure and large fluctuation in the process of drilling are often faced with drilling problems, such as spills with the deposits, well control risks and other issues. For the fracture samples, this article described the mathematical description of the fracture surface morphology and studied on extraction and reconstruction of the fracture space, then, established the fracture space seepage mathematical model and studied on the seepage mechanism and fluid-solid coupling analysis of fracture in wellbore. By comprehensive utilization of fine surface shape measurement, three-dimensional reverse reconstruction, this article takes advantage of theoretical research, laboratory experiments and numerical simulation methods to reveal the mechanism of fracture flow solid coupling. It mainly has the following contents and conclusions:(1) Through using XSM-LC non-contact precision measurement systems, this article researched natural fracture surface of three-dimensional surface features, asperity distribution laws and the surface shape parameters of fractures, and reconstructed the surface of fractures and three-dimensional space model;(2) The experimental results show that fracture width, differential pressure and drilling fluid properties are the sensitive factors affecting fluid flow velocity in a single ideal parallel fracture. Studied on the impact on the fracture seepage of rough fracture waviness and revised the fracture cube law by adopt the roughness coefficient (JRC), the research results show that the bigger asperity density, the greater the pressure is at the same asperity height and the inlet velocity and the cube law amended proved to be better comply with the experimental data;(3) Fractures seepage vary widely under the different roughness coefficient and fractures flow and velocity decreases with increasing roughness coefficient. Because the experimental fractures are the same size, fractures waviness increased along with the increase of roughness coefficient, and fluid seepage path in the fracture becomes longer, the flow is reduced. For the same roughness coefficient, with the fracture width increases, the larger of flow channel, the greater the seepage flow is;(4) Fluid flow within the fracture decreases rapidly in the initial stages of fracture closure, and the changes of fluid flow and velocity within the fracture are not obvious near the end stages of the fracture closure. Fracture seepage space decreases with the closure of fractures, and decreasing amplitude of seepage space is closely related to the degree of fluctuation and fracture surface morphology;(5) Pressure is an important controllable parameter in the fracture seepage and deformation process regardless of near-balanced drilling or underbalanced drilling. Pressure transmission speeds are quite different between the fracture and the rock matrix. Fractures can quickly re-distribute the pressure field, wellbore instability risks become great and permeability changes significantly in larger fracture width of wellbore. Stress concentration phenomenon exists in fracture closure area and fracture width smaller areas and stress is generally larger in these areas. Fracture width is an important parameter affecting the fractures and seepage deformation, an important factor in the process of effectively transformation of fractured reservoirs and leaking stoppage of fractured leakage.(6) The research of fluid solid coupling seepage mechanism of fractures can elucidate the rule of crack leakage which is usually meet during drilling and do the quantitative calculation according to the rule. The research is the basic research of plugging technology, transformation of fractured reservoir and analysis of reservoir parameters of drilling in underbalanced drilling.