Study On Methods To Determine The Spatial Distribution Of Fractures Due To Hydraulic Fracturing In Shale Reservoirs

The permeability of shale oil and gas reservoirs is very low and the oil and gas molecules in the reservoirs are very tightly adsorbed by the rock matrix,making it difficult to develop economically and effectively by conventional oil recovery methods.Therefore,the extraction of shale oil and gas requires the use of large-scale hydraulic fracturing modification technology,which injects fracturing fluid into the reservoir to fracture the rock and form a complex fracture network through pressure,thereby releasing the hydrocarbon resources in the reservoir.Hydraulic fracturing is one of the main methods to improve the extraction efficiency of low permeability reservoirs.The hydraulic fracturing process is an extremely complex physical process,and the distribution state of the fractures is influenced by various factors,such as the mechanical properties of the rock,the formation structure,and the hydraulic fracturing parameters.Due to the differences of these factors,parameters such as length,width and depth of hydraulic fractures may also vary,leading to the complexity of the fracture distribution state.Therefore,it is very important to study the quantification of the distribution of hydraulic fractures,which can more accurately predict and control the direction and extent of fracture expansion,help to better understand the mechanism of hydraulic fracturing action and improve the extraction efficiency and economic benefits of hydraulic fracturing technology.Therefore,the quantitative research on the distribution of hydraulic fractures is of great strategic importance for the exploitation and utilization of oil and gas resources in China.The thesis on the distribution quantification method of hydraulic fractures in shale oil and gas reservoirs was carried out in the following four aspects:(1)The expansion mechanism of hydraulic fractures was explored,and analysis of the effect of Young’s modulus and Poisson’s ratio on the extension of hydraulically fractured fractures to provide a theoretical basis for the subsequent research.(2)The distribution modeling study of natural fractures was carried out,and a distribution modeling method based on statistical model was proposed by analyzing the characteristics and distribution law of natural fractures,which provided a basis for the distribution prediction of hydraulic fractures.(3)The volume estimation method of hydraulic fractures was studied,the volume calculation model of hydraulic fractures was analysed,and two volume estimation methods were proposed.(4)The distribution of hydraulically fractured fractures was addressed,and a skeleton-based method for quantifying the distribution of hydraulically fractured fractures was proposed.The following conclusions were obtained:(1)During the fracturing process,rock materials with higher Young’s modulus are more difficult to produce plastic deformation,which is more likely to lead to fracture penetration and expansion.With a larger Poisson’s ratio,the rock is more resistant to deformation,making it difficult to produce large volume changes,and the fracture width formed by hydraulic fracturing is relatively small.(2)By modelling the natural fracture distribution,the more fracture bars there are in the same area,the higher the fracture density,the more intricate the relationship between fractures,and of course the better the inter-connectivity,providing a basis for the design of hydraulic fracturing parameters.(3)For the Monte Carlo algorithm,10 sets of experimental results show that the volume of fractures fluctuates greatly when the number of sampling is small,and tends to stabilise as the number of sampling continues to increase.For the ant-tracking algorithm,10 sets of experiments were also conducted,and the volume of the simulated fractures and the volume of fractures obtained by the Monte Carlo algorithm overlapped,indicating that the simulation of the ant-tracking algorithm is accurate.(4)The skeleton extraction method was verified using actual data to achieve a quantitative description of the distribution of hydraulically fractured fractures.The research results of this thesis provide theoretical and methodological support for the optimization of hydraulic fracturing technology.