Abstract

Five formation tests were undertaken in well 110/8A-5 in the Irish Sea. Pressures within the tested intervals were reduced from 16-17 MPa to c. 10 MPa. The tested intervals, which were subsequently logged by an electrical imaging tool, exhibit zones of low resistivity on opposite sides of the wellbore wall. These zones are restricted to the tested intervals and interpreted as borehole breakouts. It is inferred that the reduction in wellbore pressure associated with testing increased the stress acting on the wellbore wall, leading to failure. This confirms that such wellbore failure can be induced by reducing mud weight. Maximum horizontal stress is inferred to be orientated east-west which has implications for reservoir development, because natural and induced fluid flow will tend to be focused in that direction. With regard to the formation tests, near wellbore fracturing may result in modelled permeabilities exceeding those associated with intact reservoir rocks.

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