Petroleum Engineering 405 Drilling Engineering 1 Well Drilling Engineering Prediction of Fracture Gradients Dr DO QUANG KHANH 2 Prediction of Fracture Gradients Well Planning Theoretical Fracture[.]
Well Drilling Engineering Prediction of Fracture Gradients Dr DO QUANG KHANH Prediction of Fracture Gradients Well Planning Theoretical Fracture Gradient Determination Hubbert & Willis Matthews & Kelly Ben Eaton Comparison of Results Experimental Frac Grad Determination Leak-off Tests Lost Circulation Read: Applied Drilling Engineering, Ch HW # Well Planning Safe drilling practices require that the following be considered when planning a well: Pore pressure determination Fracture gradient determination Casing setting depth selection Casing design Mud Design, H2S considerations Contingency planning Fig 7.21 Formation Pressure and Matrix Stress Given: Well depth is 14,000 ft Formation pore pressure expressed in equivalent mud weight is 9.2 lb/gal Overburden stress is 1.00 psi/ft Calculate: Pore pressure, psi/ft , at 14,000 ft Pore pressure, psi, at 14,000 ft Matrix stress, psi/ft Matrix stress, psi Formation Pressure and Matrix Stress S =S = PP+ σ + σ overburden stress (psi) pore = pressure (psi) + matrix stress (psi) Formation Pressure and Matrix Stress Calculations: Depth = 14,000 ft Pore Pressure = 9.2 lb/gal equivalent Overburden stress = 1.00 psi/ft Pore pressure gradient = 0.433 psi/ft * 9.2/8.33 = 0.052 * 9.2 = 0.478 psi/ft Pore pressure at 14,000 ft = 0.478 psi/ft * 14,000 ft = 6,692 psig Formation Pressure and Matrix Stress Calculations: Matrix stress gradient, S =P+σ psi S P σ or = + psi/ft D D D σ S P i.e., = − = (1.000 − 0.478 ) psi / ft D D D σ / D = 0.522 psi/ft 10