Dynamic permeability change of supercritical CO2 fractured shale and its influencing factors

Based on academic thought of non-aqueous fracturing proposed in recent years,the shale cylinder specimen of diameter 100 mm and length 200 mm was fractured by supercritical CO2 first,then it was used to conduct CO2 seep-age experiment at different volume stress and temperature conditions,aiming at revealing the mechanism of permeabili-ty change in supercritical CO2 fractured shale and its influencing factors. The experimental results show that the perme-ability of fractured shale decreased due to the CO2 adsorption induced swelling. The permeability of fractured shale has a negative exponential relationship with effective stress. At the temperature range of 32 -48 ℃ ,the permeability de-creased with the increase of temperature,and the temperature sensitivity of permeability is also decreased with the in-crease of temperature. At the low pore pressure range(1 -3 MPa),Klinkenberg effect exhibits a significant influence on the permeability,which leads to the permeability decreases with the increase of pore pressure,when the pore pres-sure exceeds 3 MPa,permeability increases with the increase of pore pressure as the effective stress is the dominant in-fluencing factor. Therefore,the permeability of shale gas reservoir is commonly affected by the multiple factors such as geo-temperature,geo-stress and the pore structure of shale. Finally,the coupling relationship between shale permeability and geo-temperature,geo-stress field is established according to the experimental results.