Coupled Damage Mechanisms Of Fracture-Matrix In Tight Gas Reservoirs

Fracturing is an important technical measure to increase production of tight sandstone gas reservoir.Tight sandstone gas reservoir is characterized by low porosity,low permeability and complex pore structure.Water lock damage,sensitivity damage,fracturing fluid residue damage,proppant deformation and embedding damage,fracturing fluid damage are easy to occur in fracturing reconstruction process.These damages greatly reduce the reconstruction effect of tight sandstone gas reservoir.In view of the reservoir damage of tight sandstone gas reservoir during fracturing and reconstruction,this paper has carried out laboratory experiments on the formation damage of tight sandstone gas reservoir.The coupling damage mechanism of block system-fracture system in tight sandstone gas reservoir is studied by numerical simulation and theoretical analysis,and the flow capacity of the block-fracture system after fracturing is evaluated.The main achievements and understandings are as follows:(1)Taking the low permeability tight sandstone of ZJ block in western Sichuan as the research object,the reservoir characteristics and potential damage factors of tight sandstone gas reservoir are analyzed.The reservoir physical parameters are provided for the next study.(2)Combined with the geological characteristics of tight sandstone in ZJ block,the sensitivity damage test evaluation and water lock damage test evaluation of low permeability tight sandstone in ZJ block are carried out.The experimental results show that the water lock damage caused by the fracturing fluid filtrate invading the matrix along the fracturing wall is the main cause of the block system damage in the fracturing process.The damage factors of fracture system include fracture deformation,fracturing fluid residue,proppant embedding and deformation.The experimental results show that the residue of fracturing fluid is one of the main factors of fracture damage,and to a great extent,it affects the effective fracture length in fracturing operation.(3)The calculation model of fracture conductivity considering both proppant deformation and fracturing fluid damage is established,and the influencing factors of fracturing fracture conductivity are analyzed.The theoretical analysis shows that the diameter of proppant,the elastic modulus of proppant,the closure pressure and the concentration of sand cover have a great influence on the fracture conductivity,among which,increasing the diameter of proppant has a significant effect on the enhancement of fracture conductivity.There is a linear relationship between fracture conductivity and proppant diameter.(4)A comprehensive damage evaluation device for drilling-completion-reservoir reconstruction has been developed.The damage of tight sandstone reservoir under actual working conditions has been simulated,and the fracturing damage has been studied experimentally.The calculation model of fracture conductivity is verified by experimental data.The experimental results show that with the increase of the closed pressure,the proppant will deform and even embed into the fracture wall,resulting in the decrease of the fracturing conductivity,in which,with the increase of proppant strength,the proppant particle size increases,and the sand spreading concentration increases.The conductivity of fracturing cracks increases gradually and tends to be stable.(5)The coupling damage mechanism of block system and fracture system in tight sandstone gas reservoir is studied,and the flow capacity of the block fracture system after fracturing is evaluated,which provides a reference for the optimal design of fracturing.