The invasion of fracturing fluid into shale formations has a significant influence on the magnitude of permeability stress sensitivity
ultimately affecting shale gas well productivity. However
there remains a lack of mature theoretical evaluation methods for the influential mechanisms and characterization of stress sensitivity in water-invaded shale. To address this
novel physical simulation experiments and theoretical characterization methods were established to investigate the influence of fracturing fluid invasion on stress sensitivity in different shale flow regions
thus clarifying the relationship between shale stress sensitivity
effective stress
and water invasion degree. Results show that the initial stress sensitivity coefficient of shale exhibits a linear positive correlation with the degree of water invasion
while showing a linear negative correlation with effective stress. When the fracture water saturation reaches 0.90
the initial stress sensitivity coefficient can increase linearly by approximately 100 %
and decrease linearly by 17.86 % under the high stress of 55 MPa
accompanied by a five-order-of-magnitude permeability loss. Furthermore
the variation rate of the initial stress sensitivity coefficient with respect to water saturation and that of stress sensitivity with respect to effective stress are linearly correlated with clay mineral content and clay water absorption capacity.
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references
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