Fluid-solid Couping Simulation Of Leak-off For Fracturing Fluid Of Fractured-vuggy Carbonate Rocks In Gao-mo Block

With the in-depth exploration and development of oil and gas reservoirs in China,fractured-vuggy carbonate reservoirs have played an important role in the field of 0il and gas reservoir development because of their rich oil and gas resources.At present,the acid fracturing is widely used in fractured-vuggy carbonate reservoirs,and there are good results.However,because of the high burial depth and temperature in reservoir,some reservoirs9 acid fracturing effect is poor,then hydraulic fracturing is being gradually carried out in recent years.Fracture-cave carbonate reservoir has high elastic modulus,natural fractures are also well developed,and karst caves of different scales make a large amount of fracturing fluid leak into natural fractures or karst caves in the process of fracturing,resulting in poor stimulation effect or job failure.Based on the reservoir characteristics of Gaoshiti-Moxi block in Anyue gas field,this paper studies the fracturing fluid leak-off characteristics by using percolation mechanics theory,fi'acture mechanics theory and finite element method,this paper establishes fracturing fluid leak-off models of matrix,fracture and fracture-cavity reservoirs respectively,and simulates the fracturing fluid leak-off process under various models,at the same time,this paper analyses the influence of different factors when the fracturing fluid leaks in each leak-off process.The research results provide theoretical basis for the optimal design of hydraulic fracturing in target block.The main research results are as follows:(1)According to the characteristics of fractured-vuggy carbonate reservoirs in target blocks,starting with the physical model of fractured fluid leak-off,a fluid-solid coupling mathematical model of fractured fluid leak-off is established,and the simulation calculation and analysis of fractured fluid leak-off in fractured-vuggy reservoirs are completed by using the basic theory of finite element and the relevant method of ABAQUS.(2)For fracturing fluid leak-off in matrix reservoirs,the leak-off rate of fracturing fluid increases with the increase of permeability and porosity,decreases with the increase of viscosity,increases with the increase of displacement,and the influence of elastic modulus and Poisson's ratio is negligible.(3)For fracturing fluid leak-off model of fractured reservoirs,small-scale natural fractures are considered on the basis of matrix reservoirs.The existence of natural fracture greatly increases the leak-off of fracturing fluid.The invasive velocity of fracturing fluid increases with the increase of natural fracture length,and decreases with the increase of approximation angle and horizontal principal stress difference.(4)For fracturing fluid leakoff model of fractured-vuggy reservoirs,the existence of natural fractures and karst caves is also considered.The simulation results show that there are two abrupt changes in the leak-off rate of fracturing fluid to karst cave,one is that fracturing fluid invades natural fracture,the other is that fracturing fluid invades karst cave.The larger the size of the cave,the faster the fluid intrudes into the cave;the smaller the pressure in the cave,the faster the fluid intrudes into the cave;the number of natural fractures in the fracture-cave area will change the speed of the fracturing fluid intruding into the natural fracture and the time of the fluid intruding into the cave,which has little effect on the speed of the fluid intruding into the cave.