A New Definition on Fractal Porous Rock Damage Variable and Study on Evolution Characteristics of Porosity-permeability

Considered the fractal characteristic of rock with porosity structure, a rock damage variable which describes rock damage of the reservoir of fractal structure with hydraulic fracturing is defined, and this damage variable that describes the state of rock mass is also the number of the relative reductions as the pore radius is greater than r during arbitrary loading stage. The rock mass constitutive model of fractal pore structure and the damage evolution model of porosity and permeability are established. Taking one block of Daqing oil field as an example, the branch of rock and the variation of fractal dimension coefficient under different loading are determined in experiments, the rock damage variable, the evolution of porosity and permeability during loading process are calculated, and the following conclusions can be made: During loading process, the porosity of rock decreases, the permeability declines and the fractal coefficient descends. The calculated results coincide with the actual site.