Fracture initiation pressure and its influencing factors during sliding sleeve fracturing in cemented wells

Key words:  well cementing  sliding sleeve fracturing  fracture initiation pressure  cement sheath  horizontal stress difference  azimuth of valve

Abstract:

The oilfield practice has indicated that high fracture initiation pressure is the main problem for applying sliding sleeve fracturing technique in cemented wells. A 3D model coupled with hydraulics and solid mechanics was established to study the characteristics of the sliding sleeve fracturing in cemented wells. The fracture initiation pressure was calculated using a finite element method and rock tensile strength criteria. A case study of Tao-X well in Changqing Oilfield was conducted to verify the model, and the influence factors of fracture initiation pressure were analyzed. The results indicate that horizontal stress difference and azimuth of valve are the main influence factors to the fracture initiation pressure. The fracture initiation pressure decreases with the increase of the horizontal stress difference and increases with the increase of the azimuth of valve. The elastic modulus of the rock formation also has a significant effect on the fracture initiation pressure, the higher the elastic modulus, the greater the fracture initiation pressure needed. The effect of cement sheath on fracture initiation pressure is related to the elastic modulus of the cement and rock formation. The fracture initiation pressure increases with the increase of the thickness of cement sheath when the elastic modulus of the cement is bigger than that of the rock formation, and vice versa.