Study On Fluid-Solid Coupling In Multiple Medium And Its Influence On Seepage Law For Shale Gas Reservoirs

Shale gas reservoirs have nano micro pores,microfracture,multi-stage fracturing artificial joints,and have multi-scale and multi-media characteristics.Due to the development mode,there are lots of fracturing fluids in the seams.In the process of development,the interaction between gas liquid and solid interface and pressure change lead to the obvious coupling of flow and solid.Therefore,it is of great theoretical and practical significance to carry out two aspects of fluid solid coupling in stress field and fracturing fluid for shale gas development.In this paper,the mineral composition,micropore structure and pore size distribution of the Lower Silurian Longmaxi Formation in Sichuan gas field were analyzed.Due to the fragility of shale,artificial fractures are made by improving the Brazil splitting experiment accurately,and the characteristics of fractures were described by micro-CT scanning.On the basis of preparatory work,the seepage laws of different types of rock samples(black shale,natural microfracture,artificial fractures)were studied.The experimental study of seepage law has been carried out,and the influence mechanism of different types of pore distribution on gas seepage has been revealed.the permeability model considering the effect of cracks was established,and the effect of fracture characteristics to permeability were analyzed quantitatively.A one-way flow model considering scale effect is also established.Combined with the experimental results of seepage law,the effect of stress on different types of reservoirs is revealed.Based on the understanding of multiple medium core seepage law,the stress field coupling mechanism and influencing factors of multiple medium shale reservoirs are systematically studied.In view of the coupling effect of fracturing fluid and reservoir,the simulation experiment on injection and back of fracturing fluid is designed.Based on the characteristics of the fracture network,the distribution characteristics of the retained fracturing fluid,the main controlling factors of the retained liquid volume and the fracturing fluid backflow law are studied.The concept of "effective area"is introduced,and the effect of fracturing fluid to productivity is analyzed.The seepage characteristics of fracturing fluid in the fracture have great influence on the coupling of fracturing fluid and reservoir,and the fracture opening is the main controlling factor affecting the seepage and retention to fracturing fluid.In the process of fracturing fluid injection,there is an anhydrous zone under the influence of starting pressure gradient.When the fracture opening of the fracture is large,the retained water in the fracture will be the main component.In the process of backflow,fracturing fluid retention is more likely to occur with complex fracture networks with transverse cracks connecting main channels.The effective seepage area in fracture network is the key to productivity.On the basis of the coupling mechanism of stress field and fracturing fluid,a multi scale multilevel fractured horizontal well productivity model is established,and the production capacity is simulated with the field conditions.The results show that fractured shale reservoirs are affected by stress greatly.It is suggested that pressure control should be adopted for fractured reservoirs.The size of matrix block is greatly influenced by the fractured fractured block.When the development of micro fractures in fractured blocks is low and the fracturing effect is poor,the pressure control should be taken to improve the gas recovery.The fracturing fluid in the reservoir is not good for productivity on the whole.In the fracturing process,the injection volume should be controlled as much as possible and the damage to production capacity can be reduced.