Influence of Shale Bedding Plane on Wellbore Stability for
Horizontal Wells

doi:10.11885/j.issn.1674-5086.2013.06.30.03

Abstract

Abstract:

Brittle shale formation developed a lot of bedding plane and microfissuring in marine shale gas region of South
China. Borehole collapse problem of horizontal well in bedding plane formation has seriously hampers the development process.
Therefore based on the linear elastic mechanics model of borehole stability and the single weak-plane strength theory，the
borehole stability model for horizontal wells in bedding plane formationis is established. It considers influence of the attitude
of bedding plane，strength of weak bedding plane，rock strength，horizontal azimuth，weakening of bedding plane（water
cuts）and etc. Based on these，this paper quantitatively analyzed the effects of attitude of bedding plane and water cuts. The
results show that collapse pressure is controlled by attitude of bedding plane and horizontal azimuth，and that the borehole
stability of horizontal well is better when dip angle of bedding is 0°<θDIP<15° and 75°<θDIP<90°. Bedding weakening is one
of the important factors，which lead to borehole collapse.No matter how attitude of bedding plane change，with water cuts of
bedding increase，borehole collapse pressure increases rapidly，and the increase range of collapse pressure is about 12～18 MPa.
When the water cuts is 20%，collapse pressure increases by 37.9%.

Key words: shale gas, bedding plane, horizontal well, wellbore stability, weak plane, collapse pressure

Ma Tianshou, Chen Ping. Influence of Shale Bedding Plane on Wellbore Stability for
Horizontal Wells[J]. 西南石油大学学报(自然科学版), DOI: 10.11885/j.issn.1674-5086.2013.06.30.03.

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