Figure G-35a shows the failure envelope of a tight (low-permeability) sandstone, which is a petroleum reservoir rock. If 1 = 72 MPa and

Figure G-35a shows the failure envelope of a ‘‘tight’’ (low-permeability) sandstone, which is a petroleum reservoir rock. If σ₁ = 72 MPa and σ₃ = 42 MPa, determine the amount of pore pressure that would be necessary to fracture this reservoir hydraulically.

Figure G-35a

a 20 10 20 MPa -10 -10 -20 10 20 30 40 50 60 70 80 MPa