Study on Prevention of Micro-Annulus in Cement Sheath by Prestressed Cementing Method

doi:10.3969/j.issn.1006-6535.2021.06.019

Abstract

Abstract: The annulus pressure is more common in deep shale gas horizontal wells, which is mainly caused by the micro-annulus at the interface between casing and cement sheath. To address this problem, the generation and propagation of micro-annulus under prestressed cementing were analyzed by mechanical experimental means and numerical simulation methods, and the number of fracturing-resistant sections of cement sheath under different prestress was determined. The results showed that the lower the pressure inside the casing, the more times that the cement sheath withstood the cyclic loads on the premise of keeping the seal integrity; the micro-annulus width of 30.89 μm under cyclic load was the critical value for gas channeling. The prestressed cementing significantly reduced the initial plastic deformation and increased the plastic deformation increment; taking into account the radial prestrain generated by the casing under prestress, the prestressed cementing technology significantly reduced the micro-annulus width and increased the number of fracturing-resistant sections for cement sheath seal integrity in the multi-stage fracturing process. The higher the prestress value, the more fracturing-resistant sections before the micro-annulus appeared; with the same number of fracturing sections, the higher the prestress the smaller the micro-annulus of cement sheath. The field application results indicated that the annulus pressure of casing in deep shale gas horizontal wells was effectively reduced by prestressed cementing technology and cement slurry with low elasticity modulus. The results of the study provide technical support for the cementing of shale gas horizontal wells.

Key words: cement sheath, sealing, micro-annulus, cyclic load, shale gas, horizontal well

CLC Number:

TE256

Xi Yan, Li Fangyuan, Wang Song, Liu Mingjie, Xia Mingli, Zeng Xiamao, Zhong Wenli. Study on Prevention of Micro-Annulus in Cement Sheath by Prestressed Cementing Method[J]. Special Oil & Gas Reservoirs, 2021, 28(6): 144-150.

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