Closed-loop Extraction Method For the Recovery of Heavy Oils And Bitumens Underlain By Aquifers: the Vapex Process

Abstract

Abstract In previous papers(1,2,3) the authors described the results of injecting saturated ethane or propane vapours into a scaled twodimensional model to recover heavy oils and bitumen at or slightly above the reservoir temperature. The results were encouraging. Although the scaled oil production rates were lower than those obtained with SAGD(4), they showed that it may be possible to recover heavy oils and bitumens economically using this method in conjunction with long horizontal wells. Apart from the low heat requirement inherent in the use of saturated propane, additional advantages derived from vapex are a partial in situ deasphalting and a reduction in the content of heavy metals. The resulting oil can be lighter, of a higher quality and better suited for a direct refining. In this paper these ideas are expanded further: a development of a closed-loop extraction is described and a technique for spreading the hydrocarbon vapour underneath the oil bearing payzone is proposed to simulate the performance of a planar well. Using this concept the vapour-oil contact is greatly increased and improved production rates are obtained. The paper discusses scaled physical model results for Peace River bitumen and Lloydminster heavy oil. The mechanism involved is believed to be similar to that which was described earlier on rising fingers of liquid solvent(5). Experiments are presented that show that the rate of mobilization is a function of the areal distribution of the solvent vapour. The results demonstrate that oil production rates exceed those of the SAGD in spite of the fact that no extraneous heat is injected into the reservoir. This strategy may permit the economic production of marginal heavy oil and bitumen reservoirs. Introduction Many heavy oil reservoirs in Alberta and Saskatchewan are thin and underlain by extensive aquifers. Bottom water frequently limits the performance of primary and thermal recovery methods. Primary production is often hampered by rapid water coning, and economic recoveries are limited to about 1 to 5% of the original-oil- in-place. Thermal methods can be inefficient and uneconomical due to excessive vertical heat losses, thin pay zones, high water cuts and steam condensation in bottom water zones. Underlying zones of high water saturation are also common in bitumen reservoirs in Peace River. In Cold Lake, reservoirs fluids tend to migrate through the path of least resistance, i.e., via the bottom water zone, resulting in low recoveries and poor sweep efficiencies. Pilot or commercial thermal recovery operations in these reservoirs are either considered unsuitable or their location is chosen to maximize net pay thickness and to minimize bottom water thickness. As a result, until now reservoirs with an underlying aquifer have been of a lower commercial value to operators because of low productivities and high water cuts. It is believed that when employing a saturated hydrocarbon vapour (typically ethane or propane) in conjunction with horizontal wells to mobilize and recover viscous oils and bitumens from formations, the bottom water zone can serve as a means for providing initial injectivity.