An Investigation into the Effects of Oil-Well Cement Expansion Agent on the Integrity of Cement Sheath

Generally, the so-called expansion agent is very effective in eliminating all the micro-annuli that exist between the casing and the cement sheath or between the cement sheath and the formation. However, this approach can detrimentally affect the sealing ability of cement sheath if the expansion agent is used in an unreasonable way. For these reasons, in the present work, numerical simulations have been conducted to analyze the effect of elasticity modulus of cement sheath, the elasticity modulus of formation, the expansion rate of cement, the geo-stress on the micro-annulus caused by cement expansion, and the cement sheath expansion on the integrity of cement sheath and formation. The micro-annulus between the casing and the cement sheath has been found to decrease according to the ratio between the elasticity modulus of formation and the elasticity modulus of cement sheath. A positive correlation has been observed between the micro-annulus and the cement expansion ratio. The microannulus decreases as the geo-stress increases, but the effect of the geo-stress on the micro-annulus is much smaller. In conclusion, the expansion agent is suitable for the formation in which the elasticity modulus is higher than the cement sheath.