Methods for producing fluid migration resistant cement slurries

摘要

Methods including providing a wellbore in a subterranean formation; providing a proposed cement slurry; calculating a fluid migration threshold; manipulating the proposed cement slurry based on the fluid migration threshold so as to produce a fluid migration resistant cement slurry; introducing the fluid migration resistant cement slurry into the wellbore in the subterranean formation; and curing the fluid migration resistant cement slurry in the wellbore in the subterranean formation.

主权项

1. A method comprising:
providing a wellbore in a subterranean formation; providing a proposed cement slurry comprising a base fluid and a cementitious material; calculating a fluid migration threshold pressure, the fluid migration threshold pressure (PC) being the critical pressure required to cause a break in the proposed cement slurry during hydration and based on elastic fracture mechanics due to crack propagation shape, and calculated using the formula:PC=KIC6/5⁢π3/5⁡(1-v2)(12⁢⁢Vbub⁢E)1/5,where KIC is a tensile fracture toughness of the cement slurry, ν is Poisson's ratio, E is Young's modulus, and Vbub is an initial volume of a crack propagation fluid bubble;
manipulating the proposed cement slurry based on the fluid migration threshold pressure to maximize the rate of increase over time of the fluid migration threshold pressure and produce a fluid migration resistant cement slurry, such that the fluid migration threshold pressure exceeds a formation pore pressure and is achieved at or above a time of intersection with a net formation pore pressure (ΔPnet) determined by the formula: ΔPnet=ΔPcement−ΔPob, where ΔPcement is a transient hydrostatic pressure drop in the proposed cement slurry during hydration and where ΔPob is an overburden pressure between initial hydrostatic pressure of the proposed cement slurry and the formation pore pressure, wherein the proposed cement slurry is manipulated by adding, removing, or adjusting an amount of the base fluid, the cementitious material, or a combination of the base fluid and the cementitious material; introducing the fluid migration resistant cement slurry into the wellbore in the subterranean formation; and curing the fluid migration resistant cement slurry in the wellbore in the subterranean formation to form a cement sheath therein.