For these two failure modes, the mudcake strength is an important factor controlling the critical wellbore pressure for mudcake rupture and thus FLP, although it has a small influence on FIP.
The rupture of the mudcake over the fracture mouth may have two distinguishing failure modes (Cook et al. 2016): (1) tensile failure the mudcake is pulled apart by the opening fracture as shown in Fig. 15b, and (2) shear failure the mudcake is pushed into the fracture by wellbore pressure as shown in Fig. 15c.
The present work is devoted to understand the effects of MCSAs on the physical and chemical alteration of the mudcake and provide a new insight into the microstructure of ITZ between the cement and mudcake.
However, the mudcake can transmit part of the radial stress exerted by the wellbore fluid on the inner surface of mudcake to the wellbore wall, depending on the yield strength and thickness of the mudcake.
Despite very low permeability of the mudcake (e.g., 10−3 mD), neglecting the permeable nature of the mudcake, i.e., assuming the mudcake is impermeable, may lead to substantial overestimation of FIP.
Permeability of the mudcake is another important parameter, controlling fluid flow through the mudcake and pore pressure variation around the wellbore.
However, despite the low permeability of the mudcake, e.g., 10−3 mD, the FIP with a permeable mudcake is still much lower than that of an impermeable wellbore.
The permeabilities of the mudcake and formation are (K_{1}) and (K_{2}) ((K_{2} > K_{1})), respectively.
(5) Despite very low permeability of the mudcake (e.g., 10−3 mD), neglecting the permeable nature of the mudcake, i.e., assuming the mudcake is impermeable, may lead to substantial overestimation of FIP. (6) FLP is different from FIP when a mudcake exists on the wellbore wall.
