54th U.S. Rock Mechanics/Geomechanics Symposium,
28 June - 1 July,
physical event cancelled
2020. American Rock Mechanics Association
6 in the last 30 days
23 since 2007
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Mechanical and filtration properties of the rock are important parameters for sand production studies. In this paper, we investigate permeability of the plastic zone around borehole using experiments and numerical simulations. Experiments on cylindrical samples with central through hole made of artificial sandstones of large size were conducted to study the plastic zone permeability. Numerical modelling of the experiment was performed on DEM software. The experimental and numerical results clearly indicate the formation of a plastic zone around a hole. Plastic zone permeability is much less than the intact zone permeability, and dependent on the applied stresses and fluid pressures.
Poroelastoplasticity analysis of stresses around a hole in a cylindrical sample suggests that the material behaves elastically until the effective stresses fulfill the failure criterion. After that the material state changes from elastic to plastic, and plastic zone around a hole is formed. Plastic zone properties such as porosity, permeability, strength may significantly differ from the elastic zone properties.
There were few previous researches on the plastic zone permeability. According to Bratli and Risnes (1981), the plastic zone has varying permeability, while its value is considered to be ten times less than intact zone permeability in Risnes et al., (1982). Daigle et al., (2017) conducted numerical analysis of the depleted North Sea reservoir, and found that the permeability in the near-wellbore area is reduced by 3% compared to the reservoir permeability.
A typical shearing behavior of a weak sandstone can be characterized as volumetric contraction followed by expansion (Kozhagulova et al., 2019). In addition, bond breakage precedes particle breakage in weak sandstones composed of strong particles and weak cement. This bond breakage is associated with plastic deformation and thus by formation of the plastic zone. The initial contraction implies reduction in both porosity and permeability of the plastic zone. According to Zhu and Wong (1997), particle breakage and pore collapse can be considered as a possible reason of the permeability reduction in weak sandstones at around peak stress values. Pore collapse mechanism due to bond breakage is applicable for sandstones with strong particle and weak cement.
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