For shale gas reservoirs with the characteristics of bedding planes developed, hydrated easily and strong anisotropy of the mechanical properties, this paper couples conventional logging, image logging and real-time drilling data with laboratory rock mechanical and in-site stress tests, and establishes a wellbore stability analysis model for shale reservoirs. This analysis covers weak bedding planes, mechanical anisotropy and time effects. Besides, the effect of these above factors on the wellbore stability for horizontal wells in shale reservoirs is studied, and wellbore collapse mechanism for the shale reservoirs in Sichuan Basin is also analyzed.

Based on the established wellbore stability analysis model, this paper analyses the well W-H1, the analysis results are in good agreement with real drilling data.

Study and field application results indicate that weak bedding plane effects mainly affect wellbore collapse of horizontal wells for shale reservoirs, which differs from conventional sand reservoirs and carbonate reservoirs, even for the vertical wells in the shale reservoirs.

The study provides a theoretical basis for W-H1 well drilling and completion design, such as drilling fluid design, wellbore structure optimization and completion method optimization, etc.

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