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Journal of Mining Sciences

2021 year, number 1

Mechanism of Annular Space Unsealing during Hydraulic Fracturing

A. M. Svalov
Institute of Oil and Gas Problems, Russian Academy of Sciences, Moscow, 119333 Russia
Keywords: Hydraulic fracturing, coal seam drainage, rock stress-strain behavior, annular space unsealing, borehole reaming, bow springs centralizer


The article discusses the mathematical modeling results on formation of concentration zones of failure stresses in annular space of a well during hydraulic fracturing of productive formations from vertical or nearly vertical boreholes. The rigid connection between the cement lining and rocks fails because of a thin clay layer in-between, which leads to unsealing of the annular space and to various troubles, including environmental implications. To prevent annular space unsealing during hydraulic fracturing, it is proposed to ream out borehole in the area of contact with the productive stratum roof, and to install a bow springs centralizer on this level then.