Evaluation on stress sensitivity of multiscale pore and fracture in shale based on LF-NMR

Explosive fracturing of shale with in⁃situ methane is a revolutionary technique.To investigate the stress sen⁃ sitivity of multiscale pore⁃fracture in fractured reservoir，the T2 spectrum tests were conducted on intact shale core Y1， self⁃supported fractured core Y2 and supported fractured core Y3 with the Longmaxi shale based on in⁃situ LF⁃NMR. Besides，NMI was also conducted on core Y2.A new classification method of multiscale pores in shale was put forward based on theoretical analysis.Also，the change of compressibility of multiscale pores with confining pressure were stud⁃ ied.Results show that the volume of pores with different scales decreases with an increase of confining stress.The pores with larger scales relate to more obvious decrease.However，the volume of mesopore increases during compression， which may be caused by water migration from fractures to mesopores.There is an obvious difference among the com⁃ pressibilities of pores with various scales，and a big pore relates to a high compressibility and strong stress sensitivity. Existence of fracture leads to a significant increase in the stress sensitivity of shale，while the introduction of proppant markedly reduces the fracture compressibility.Besides，with the increase of stress，the compressibility of pores with different sizes tends to decrease followed by a negative exponential function.The decrease of micropore compressi⁃ bility is relatively small，followed by mesopores，and the decrease of fracture compressibility is the largest.