Effect of faults on hydraulic fracture propagation in coal seam

Key words:  coal seam  slump fault  hydraulic fracturing  crack propagation

Abstract:

Considering the influence of sub-fault or slum fault in the coal seam on the fracture propagation of hydraulic fracturing, the effects of approximation angle, horizontal principal stress difference, and coal and rock elastic modulus difference on hydraulic fracture propagation direction were investigated using the theoretical analysis and numerical simulation in a two-dimensional physical model. The judgment criterion of forming effective fracture through the cracking passing the fracture was established. And the critical curve for the approaching angle-horizontal principal stress difference of the coal penetrating crack, which was formed by the hydraulic fracture passing the fault, was fitted out under given coal-rock mass parameters. It is found that the approximation angle, horizontal principal stress difference, and elastic modulus of coal-rock mass play the major roles on fracture direction. Under the circumstance of low principal stress difference, smaller approaching angle, and higher roof elastic modulus, the fault is easy to produce plane tensile failure. When the approaching angle-stress difference coordinate point is above the curve, the crack will pass through the fault plane into the roof. When the angle-stress difference coordinates of point is under the level curve, cracks will be extended to the lower coal seam forming upper and lower coal seam cracks.