Heterogeneity and depth rule out steam injection and in-situ combustion processes for heavy-oil recovery in deep naturally fractured reservoirs (NFR). Once it is controlled by a proper injection scheme and the consumption of air injected through efficient diffusion into the matrix, low temperature air injection (LTAI) can be an alternative technique for heavy-oil recovery from deep NFRs.

Limited studies on light oils showed that this process was strongly dependent on an oxygen diffusion coefficient and matrix permeability, both of which are typically low. A new approach, i.e., the addition of hydrocarbon solvent gases into air is expected to improve the diffusivity of the gas mixture and to accelerate the oxidation reaction to breakdown asphaltenic molecules effectively. This improves the gravity drainage recovery from the matrix. To study this new idea called low temperature air-solvent injection (LTASI), laboratory tests were performed by immersing heavy-oil saturated cores into air¬ solvent filled reactors to determine the critical parameters on recovery, diffusion coefficient, oxidation kinetics, viscosity reduction, and gravity drainage rate.

It is imperative that enough time is given for the diffusion process before injected air filling to fracture network breakthrough. This implies that huff and puff injection is an option as opposed to the continuous injection of air. A high recovery factor was obtained by soaking a single matrix in an air-solvent chamber at static conditions rather than with air only. The period of pressure stabilization was faster for the air-solvent mixture atmosphere than in 100% solvent. The asphaltene content was lowered more in the air-solvent chamber than in a 100% air case.

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