Fracture Network Modeling And Water Sealing Parameters Optimization Of Underground Oil Storage Caverns

Along with the economy rapid development,underground water-sealed oil storage for the purpose of market and military demand has been favored by all countries in the world.It is particularly important for oil exploitation,storage and pollutant disposal to carry out in-depth study of fractures.The geometric parameters of fractures not only determine the mechanical properties and permeability characteristics,but also provide important data support for the design,evaluation and safe operation of underground water-sealed oil storage caverns.Therefore,it is the cornerstone of the design and analysis of large underground oil storage to obtain reasonable and accurate geometric parameters of fracture structural planes and establish an effective fracture network model.As the theoretical basis for the safety construction of underground oil storage,water seal evaluation is the key to the success of underground oil storage project.Therefore,it is great scientific and important to study the water seal of underground water-sealed caverns to ensure the safety of oil storage.Aiming at this key scientific problem,the cause of boundary effect in fracture network simulation is revealed and the method of weakening boundary effect is put forward through a large number of simulation and analysis of fracture network.A method for weakening the boundary effect of computer simulation is proposed.Different methods of trace length estimation are analyzed and their applicability rules are revealed based on computer fracture network simulation and field outcrop.The sampling window optimization method is established.The sensitivity of fracture network geometric parameters to permeability is analyzed,and a permeability estimation model directly related to fracture geometric parameters is established.The water sealing performance of underground water-sealed caverns is optimized based on the full factor experimental design.The results are as follows:(1)Different methods of trace length estimation are analyzed based on computer fracture network simulation and field outcrop.The effects of fracture density,real trace length,trace length distribution and sampling window location are considered.The applicability of these methods is revealed.The optimization method of sampling window is established,which has guiding significance for trace length estimation and error correction.(2)The causes of boundary effect are revealed,and the method of weakening boundary effect is proposed,through a lot of simulation and analysis of fracture network.A two-dimensional fracture network generation program considering boundary effect is developed by using MATALB.On the basis of the two-dimensional fracture network,a three-dimensional fracture network generation program is compiled with MATLAB based on the platform of MATLAB WITH COMSOL.COMSOL calls this program to generate a three-dimensional fracture network model.The established model maximizes the use of known information,reduces the boundary effect of computer modeling,ensures the validity of the generated model,and lays a foundation for the study of mechanics and flow of fracture network model.(3)Based on the fracture parameters obtained in the field,the influence of the geometric parameters of the fracture network on the permeability is analyzed by using the established two-dimensional fracture network model.The main controlling factors of the permeability are put forward.The permeability estimation model directly related to the geometric parameters of the fracture network is established.The research results can be applied to the study of underground oil storage,gas storage and other complex fractured rock mass.(4)The main factors affecting the water seal of underground oil storage,such as permeability,water curtain hole pressure,water curtain hole spacing,water curtain hole angle,distance between water curtain tunnel and main cavern,length of water curtain hole and oil and gas pressure,and their second-order and third-order interaction are studied with full factor design and COMSOL numerical simulation.The sensitivity law of different factors is revealed.A regression model for the main effect and the second-and third-order interaction effect of water inflow in caverns is proposed.The results can be used for reference and evaluation in the preliminary design underground water sealed caverns.