Borehole failure resulting from formation integrity (leak-off) testing in upper marine sediments offshore

Document Type

Article

Publication Date

1-1-1998

Abstract

This paper presents the results of a theoretical study, supported with the finite element analysis, into potential loss of external integrity around a casing shoe resulting from leak-off testing (LOT) in upper marine sediments (UMS). Three types of possible failures from LOTs were considered: vertical fracture, horizontal fracture, and a chcmnel outside cemented annulus. It is proved in the paper that vertical fracture is the most unlikely failure of the three. The other two types of failurecan be distinguished by different values of propagation pressures. Although horizontal fractures are initiated at low pressure in the plastic zone around the wellbore, they cannot propagate beyond the plastic zone until wellbore pressures exceed overburden pressures. Annular channels, on the other hand, may propagate upwards at pressures lower than overburden pressure. The paper shows that these channels are initiated at pressures equal to the contact stress between cement and rock and their propagation pressures are on average 3.5-fold greater than contact stress. It is also explained how to identify the UMS with high risk of annular channeling during LOTs. © 1998 by ASME.

Publication Source (Journal or Book title)

Journal of Energy Resources Technology, Transactions of the ASME

First Page

111

Last Page

117

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