Heavy oil occurring in carbonate reservoir, mostly fractured, is an important resource which accounts for one third of the total heavy oil world-wide. However production from such reservoir is challenging, due to very high oil viscosity. The Vapor Extraction (Vapex) process, a newly developed Enhanced Oil Recovery technique, has been studied theoretically and experimentally for conventional heavy oil reservoirs. While applicability of this process in naturally fractured reservoir has not been addressed yet.
In this work, vapor extraction process was studied by using a laboratory cell which consists of a matrix block surrounded by horizontal and vertical fractures. Scaling analysis was used to scale up the Vapex process in fractured reservoirs and compare the involved forces in both experimental model and real reservoir. Moreover, for extrapolating the laboratory results to reservoir condition, a numerical model has been developed by CMG simulation software and was validated with experimental data.
Experimental results indicate significant difference in the pattern of solvent flow in fractured model compared with the conventional model and also presence of fracture network can compensate the low permeability of matrix block and enhance the whole process.
The exploitation of heavy oil and bitumen is one of primary interest to many oil companies due to the decline of conventional oil reserves. The magnitude of these resources worldwide is of the order of 1 trillion m3 (about 6 trillion bbl) of oil in place. Currently, thermal processes are applied as enhanced oil recovery (EOR) processes to recover heavy oil. With thermal recovery processes, the viscosity is reduced by heating the reservoir. The viscosity of heavy oil and bitumen can also be reduced by addition of solvents. The energy losses inherent in the thermal processes may be avoided if a solvent is used instead of steam1.
In Vapex process, light hydrocarbon vapors or their mixtures with non-condensable gases are employed instead of steam to extract heavy oil or bitumen from the formation2. This process is regarded as an alternative EOR method to the Steam- Assisted Gravity Drainage (SAGD) process. Contrary to thermal processes, the Vapex process can be operated at reservoir temperature with no heat loss. Vapex can be used as an alternative method to recover the heavy oil and bitumen from reservoirs where thermal processes are not suitable for heavy oil recovery. These reservoirs include thin reservoirs, carbonate reservoirs with low-permeability, vertical fracture, low porosity and low thermal conductivity where the heat capacity per unit volume of contained oil is high, and reservoirs underlain by aquifers and/or overlaying by gas caps. Such characteristics as low energy consumption, low environmental pollution, in situ upgrading, and lower capital costs compared to thermal processes, make the Vapex process attractive for further investigation and possible field application instead of currently used thermal processes.
A number of experimental studies on the Vapex process have been performed on conventional models so far, of which the works of Butler and Mokrys3, Das and Butler4,5, Jiang6, Boustani7 and Yazdani8 can be mentioned.
