文档介绍：Lesson 4B Fracture Gradients - cont’d Harold Vance Department of Petroleum Engineering Fracture Gradients - cont’d Radial and Tangential Stresses near the Wellbore Stresses in Rock near Wellbore Effect of Anisotropic Stresses Onshore vs. Offshore Fracture Gradients Fracture Gradients in Inclined Wellbores Oil Based and Water Based Drilling Fluids Harold Vance Department of Petroleum Engineering Fracture Gradients - cont’d Read: Ch. 4 AWC to Page 50 Harold Vance Department of Petroleum Engineering Stress concentrations around a borehole in a uniform stress field Tension pression Harold Vance Department of Petroleum Engineering Combined effect of overburden stress and wellbore pressure Harold Vance Department of Petroleum Engineering Example Given: Formation depth = 10,000’ Poisson’s ratio = Pore pressure grad = .433 psi/ft Hole diameter = in Mud density = ppg Harold Vance Department of Petroleum Engineering Example Estimate the horizontal stress if the rock behaves in an elastic manner Solution: Eq sH = [m/(1-m)](sob-pp)+pp sH= [/(1-)](1**10000)+4330 sH=5929 psi Harold Vance Department of Petroleum Engineering Example Effective horizontal stress (a = ) seH = sH - a*pp = 5929 - 4330 seH = 1599 psi Harold Vance Department of Petroleum Engineering Example 2. Estimate the tangential and radial stresses at the borehole wall if the horizontal stresses are equal. sr = pw sr = 4330 psi st = sH1 - sH2 - pw -2(sH1 - sH2)cos2q = 5929+5929-4330-0 = 7528 psi Harold Vance Department of Petroleum Engineering Example The corresponding effective stresses are: ser = 4330-4330 = 0 psi set = 7528-4330 = 3198 psi Harold Vance Department of Petroleum Engineering