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Two Failure Mode for Unconsolidaated Rock

Author:Admin  Time:2013-9-14 7:39:56

For the horizontal well in unconsolidated sandstone reservoir, two formation rock failure patterns were put forward,one of which is the pattern of fracture initiation and extension, another is plastic compaction packing. The process and mechanism of outsidecasing plastic packing in horizontal well was analyzed. Based on the formation stress and rock strength distribution near wellbore, a formation rock failure recognition model was developed. With the model, the critical failure flowing pressure profile along the wellbore trajectory can be clarified to predict the initial breakdown point. The results show that the rock failure pattern depends on formation stress distribution, rock strength and job parameters. With bottom hole pressure increasing, when radial principal stress achieves rock anticompressing strength firstly, rock would be broken down by the failure pattern of plastic compaction packing. Contrarily, if the wellbore tangential stress overcomes the rock antitensile strength firstly, the rock fracturing occurs. Under the high pressure squeezing conditions, the strong consolidated rock with high strength tends to be broken down by pattern of fracturing, and the unconsolidated rock with low strength is more easily to failure by the pattern of plastic compaction packing. Due to the nonuniformity of formation stress and rock strength along wellbore, the critical broken pressure of two failure patterns in nonhomogeneous obviously along horizontal wellbore trajectory.

The above study result is published by Journal of UPC(Natural Science Edition).

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