THEORETICAL MODEL ABOUT FRACTURE POROSITY, PERMEABILITY AND STRESS FIELD IN THE LOW-PERMEABILITY SANDSTONE

Aiming at low-permeability sandstone, based on the principles of geological mechanics, using relationship between fracture parameters and stress field as a bridge, on the premise of reasonable preference of fracture criteria, through methods of tests and theoretical derivation, this paper establishes mechanical model between stress-strain and fracture parameters(porosity and permeability)to develop a set of quantitative methods. Results show that combining energy method with fracture criteria is effective approach to confirm the relationship between stress field and fracture parameters, after inner stress state reaching or exceeding failure conditions the fracture aperture, density will increase with strain energy density. At the same time, it is found that fractures in rock commonly formed under palaeostress field and their aperture and density were much larger than the present. Consequently, we can understand that current stress field goes against producing fractures and fracture aperture can be figured out through positive stress and shear stress acting on fracture face. Finally, Great success has been achieved in middle reservoirs of the third Shahejie Formation of Block Shishen100 in Shinan Oilfield by applying the program.