Low temperature air injection (LTAI) can be a possibility if injected air diffuses into matrix effectively to oxidize oil in it creating enhanced gravity drainage of lower viscosity oil. However, early breakthrough of air with partial consumption of oxygen due to the highly conductive nature of the reservoirs is a concern. Once it is controlled by proper injection scheme and consumption of air injected through efficient diffusion into matrix, LTAI can be an alternative technique for heavy-oil recovery from deep NFR.
Limited number of studies on light oils showed that this process was highly dependent on oxygen diffusion coefficient and matrix permeability. In this process, oil production is governed by drainage and stripping of light oil components has a greater effect on recovery than the swelling of oil.
In the present study, static laboratory tests were performed by immersing heavy-oil saturated porous media into air filled reactors to determine critical parameters on recovery; diffusion coefficient and gravity drainage rate. A data acquisition system was established for continuous monitoring of pressure at different temperatures. Also analyzed was the possibility of hydrocarbon gas additive to air to enhance diffusion into matrix. A numerical model of air diffusion into a single matrix was created to obtain diffusion coefficient through matching the lab results. Then, sensitivity runs were performed for different matrix properties and composition of injected gas (air and hydrocarbon).
It is imperative that enough timing is required for diffusion process before injected air filling to fracture network breakthrough. This implies that huff and puff type injection is an option as opposed to continuous injection of air. The optimal design and duration of the cycles were also tested experimentally and numerically for a single matrix case.