As the pore pressure increases so does the fracture

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Unformatted text preview: the above equations, Hubbert & Willis apparently consider only the variation in pore pressure gradient. Matthews & Kelly also consider the changes in rock matrix stress coefficient, and in the matrix stress ( Ki and σ i ). Fracture Gradients 1.11- 28 Summary of Results 4 Ben Eaton considers variation in pore pressure gradient, overburden stress and Poisson’s ratio, and is probably the most accurate of the three methods. The last two methods are actually quite similar, and usually yield similar results. Fracture Gradients 1.11- 29 Similarities Ben Eaton: P S −P γ + F= * D 1− γ D σ Ki P F= + D D Matthews and Kelly: Fracture Gradients 1.11- 30 Fracture Gradients 1.11- 31 Experimental Determination of Fracture Gradient The leak-off test 4 Run and cement casing 4 Drill out ~ 10 ft below the casing seat 4 Close the BOPs 4 Pump slowly and monitor the pressure Fracture Gradients 1.11- 32 Fracture Gradients 1.11- 33 Fracture Gradients 1.11- 34 Fracture Gradients 1.11- 35 Fracture Gradients 1.11- 36...
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