Experimental and Numerical Study of Steam Flooding in Fractured Porous Media

Abstract

Abstract Extra heavy oil and bitumen reservoirs constitute a huge proportion of total world oil reserves. Thermal recovery and steam based methods are the most widely used recovery methods in these kinds of reservoirs. Steam injection into fractured heavy oil reservoirs to recover matrix oil has been considered as an efficient EOR method. However, mechanism of steam injection is more complex in fractured reservoirs than in conventional reservoirs. Evaluation of steam injection in fractured porous media requires good understanding of the physical processes between rock and fluids in matrix and fracture. In fact recovery could be a combination of several mechanisms such as viscous forces, capillary imbibition, thermal expansion and gravity drainage. This paper presents experimental and simulation study of steam flooding in fractured porous media that contains Athabasca heavy oil. Some PVT properties of Athabasca crude oil have been measured experimentally and simulation study was accomplished using a numerical thermal reservoir simulator. A single horizontal fracture and two surrounding matrix blocks have been defined to verify the performance of steam injection in a 20 cm long sandstone core with a permeability of 640 mD saturated with Athabasca heavy crude. Considering a fractured system, sensitivity analyses were focused on the effect of injection rate, fracture permeability and steam quality. The most important conclusion is that there is an optimum steam temperature and quality for most efficient steam injection. The permeability of the fracture should be low considering both oil production and steam oil ratio (SOR), which is a measure of economy. Matrix permeability of 640 mD in sandstone core provides satisfactory recovery and SOR. Higher matrix permeability can cause very high SOR and affect the economy of the process. Results also clearly show that higher injection rate improve the oil recovery. However, SOR should also be considered at the same time. There is a trade-off between recovery and SOR. It is also clear that lower fracture width shows better recovery while causing high injection pressure at the inlet.