Study On Flow Law Of Shale Gas Under The Influence Of Stratifications And Fractures

By means of core analysis,outcrop observation and logging,it is found that many stratifications and fractures developed in shale gas reservoirs,which have an effect on shale physical properties,rock mechanics properties and gas flow.Through the investigation of literatures,domestic and foreign scholars have established the theory of nonlinear multi-scale flow of shale gas for the complex and changeable shale gas flow space,but these theories do not consider the influence of stratifications and fractures.In addition,domestic and foreign scholars have also carried out a lot of research on the influence of stratifications and fractures on shale rock mechanics anisotropy,so as to provide parameters or theoretical basis for reservoir reconstruction of shale gas reservoir.On the whole,the study on the influence of stratifications and fractures on shale gas flow is less and to be strengthened.This paper uses the combination of experiment and theory to carry out research.Based on the previous study,the multi-scale apparent permeability model of-shale gas considering desorption and stress sensitivity is established based on the seepage mechanism of shale gas reservoir under formation conditions.Secondly,the shale flow experiments with different stratifications and fractures characteristics is conducted.Finally,based on the apparent permeability model and the flow experiment results,the mathematical model of the fracturing horizontal well of the gas-water two-phase shale gas reservoir is established.After validating the model,the basic parameters of shale gas reservoir,the characteristics of stratifications and fractures and the reservoir reconstruction parameters on the perfomance of fractured horizontal well were analysed.The main work and conclusions of this paper are as follows:(1)The basic physical properties,microcosmic pore structure,stratification fracture development characteristics,shale gas reservoir mechanism and migration mechanism of shale gas reservoir were analyzed.The shale gas reservoir has the characteristics of ultra low pore and ultra low permeability,the shale gas is usually stored as free gas,adsorption gas and dissolved gas in nanosphere pores and cracks.The flow mechanism of shale gas is complex,showing the obvious non-Linear multi-scale features.(2)Based on the Beskok-Karniandakis model,the apparent permeability model of shale considering stress sensitivity and desorption was established.The influence of stress sensitivity and desorption on apparent permeability of shale was analyzed by this model.When the pore radius is less than 5 nm,the apparent permeability of shale increases with the decrease of pressure,and the apparent permeability of shale increases with the decrease of pressure when the pore radius is less than 5 nm.(3)Shale stress flow experiments with different stratification directions and different stress characteristics of shale stress are carried out.The experimental results show that the permeability of the shale in the parallel stratification direction is greater than that in the vertical stratification direction(up to an order of magnitude),and the parallel stratification direction slip effect is stronger than the vertical permeability direction.The stress sensitive experiment results show that the existence of the fracture Which is the main seepage channel of shale gas,but the fracture permeability is sensitive to effective stress and shows strong stress sensitive characteristics.(4)Based on the calculation model of apparent permeability of shale and the shale flow characteristics of different stratification and fractures,the mathematical model of gas-water two-phase in shale gas reservoir is established,and the finite difference method is used to solve The numerical solution of the model is analyzed and the reliability analysis and sensitivity analysis are carried out.The stratigraphic development increases the heterogeneity of shale reservoirs,and the horizontal stratification leads to significant differences in lateral and vertical permeability of shale,and fracture development also makes the permeability of different locations in reservoirs uneven,but From the results of numerical simulation,for strong heterogeneity,can be achieved through the reservoir transformation technology to effectively increase production.