The behaviour of minerals in Cold Lake oil sands under dry combustion conditions

In the in situ or underground combustion oil recovery process, ignition is initiated at an air injection well and a combustion zone is propagated underground from this well to the production well. Under these conditions, the reservoir minerals undergo structural changes, new mineral phases are synthesized and their grain sizes are altered. These reactions control the porosity and the permeability of the reservoir. Cold Lake whole tar sand was subjected to air flow thermal conditions encountered under fire flood. The very fine-grained minerals were separated from the burnt oil sand as well as from the sand fraction from which bitumen had been removed with organic solvents. These mineral fractions were examined by 9.4 and 34 GHz electron paramagnetic resonance (EPR), Fourier transform infra-red (FTIR) and X-ray diffraction (XRD) spectroscopy. The EPR results indicate the presence of Mn²⁺ impurity ions in carbonates and Fe³⁺ impurity ions in kaolinite and illite clays. A broad transition at g ≈ 2 is attributed to the presence of Fe₂O₃ and a very broad transition at g 12 is attributed to the presence of Fe₃O₄. In addition, the EPR and FTIR results indicate that the bitumen is adsorbed on the mineral fraction. XRD shows that combustion produces a significant amount of Fe₂O₃ and reduces the quantity of kaolinite, illite and smectite clay. Treatment of both mineral fractions with dilute H₂SO₄ and HCl acids showed that the organic fraction adsorbed on minerals is immune to the acid attack while Fe₂O₃ and Mn²⁺ are removed.