Characterization of wellbore casing corrosion product as a permeable porous medium

Abstract

Leakage along wellbores is of concern for a variety of applications, including sub-surface fluid storage facilities, geothermal wells, and CO2 storage wells. We have investigated whether corroded casing is permeable to gas and can serve as a leakage pathway along wellbores. Three specimens were prepared from laboratory steel plates corroded using different mechanisms to reflect different possible field conditions and produce a variety of corrosion rates. Single-phase gas flow measurements were made under a range of gas pressures to investigate flow in both the viscous and visco-inertial flow regimes. Tests were conducted at different confining stresses (range from 3.45 to 13.79 MPa) following both loading and unloading paths. The gas flow test results suggest corroded casing can serve as a significant leakage path along the axis of a wellbore. Transmissivity was found to be sensitive to the variation in confining stress suggesting that the corrosion product is deformable. Gas slip factors and the coefficients of inertial resistance of the corrosion product were comparable to those available in the literature for other porous media. Post-test examination of the corrosion product revealed it to be a heterogeneous, mesoporous material with mostly non-uniform slit type porosity. There was no discernable difference in the composition of corrosion product from specimens corroded by different mechanisms.