Stress Sensitivity Characteristic And Mechanism Of Fractured Reservoir Under The Action Of Temperature And Fluid

With the development of global economy,unconventional oil and gas resources have been developed vigorously and become a necessary way to relieve the pressure of energy demand in many countries.Along with the advancement of exploration and fracture modification technology for low-permeability reservoirs worldwide,the production and development of fractured oil and gas reservoirs are becoming more and more common.Due to the presence of natural fractures in reservoirs,fractured reservoirs are more inhomogeneous than conventional ones,and the mechanisms of temperature and fluid factors are more complex.Therefore,based on previous studies,this thesis takes the fractured sandstone reservoir of Ahe Formation in Kuqa Depression as the research object and conducts stress sensitivity experiments based on artificial seam-making treatment rock samples as well as a series of experiments such as XRD,mercury pressure and low-temperature liquid nitrogen to reveal the characteristics and microscopic mechanism of stress sensitivity of rocks under the action of temperature and fluid,and analyze its impact on oil and gas exploration and development.The results show that(1)the fractured reservoirs of the Jurassic Ahe Formation in the Kucha Depression are strongly stress-sensitive reservoirs,and the permeability of fractured sandstone reservoirs will be irreversibly damaged when subjected to effective stress.(2)Temperature affects the stress sensitivity of fractured reservoirs,and the permeability changes of rock samples under different temperature conditions show obvious non-linear variation characteristics when subjected to effective stress.In the range of room temperature～100℃,the higher the temperature,the greater the permeability damage of rock samples,and the lower the temperature,the smaller the permeability damage of rock samples;when the temperature exceeds 100℃,the higher the temperature,the less the permeability of rock samples lost,and the lower the temperature,the more the permeability of rock samples lost.(3)At room temperature～105℃,only weak thermal expansion of mineral components in the rock will occur.After the temperature reaches 105℃,a large amount of water is dissipated,the permeability damage rate and irreversible permeability damage rate are obviously reduced,and the stress sensitivity of the rock is enhanced.(4)Mineralized fluids affect stress sensitivity of fractured reservoirs.Rock samples under different mineralized fluid conditions show obvious non-linear variation characteristics of permeability change when the effective stress is applied.The higher the mineralization degree of fluid in the pure water and low mineralization degree water(50g/L and 100g/L)stages,the smaller the permeability damage of rock samples;the higher the mineralization degree of fluid in the high mineralization degree water(200g/L and 300g/L)stages,the larger the permeability damage of rock samples.High mineralization stage of water treatment on rock samples when the role of the most obvious.(5)Pure water action on the rock mainly through the clay minerals hydrated swelling with the formation of water film on the grain surface to reduce the permeability of the rock.Low mineralization fluid stage,some mineral components are separated,exfoliated and redissolved,so that the rock shows the change pattern of lower damage rate with increasing mineralization.In the high mineralization fluid stage,minerals crystallize and then remain or block among the pores,throats or fractures,forming a higher permeability damage rate and irreversible permeability damage rate,and showing strong stress sensitivity.There are 31 figures,16 tables and 125 references in the thesis.