The Steam-Assisted Gravity Drainage (SAGD) process, which usually employs horizontal injection and production wells has been applied successfully in producing heavy oil reservoirs. It allows high recoveries to be obtained, at high rates without significant bypass of steam. However, SAGD process. due to, the heat loss to the overburden and adjacent formations can only be used for thick reservoirs with relatively high porosities and oil saturations if there is to be an economic oil/steam ratio.
The Vapex process, which uses light hydrocarbon vapours 10 extract heavy oil from the reservoir is studied experimentally in the work described in this paper using a new, longer, scaled, packed model. In the process that evolved from the work. liquid solvent (propane, butane or mixtures) is injected with a small amount of non-condensible gas through a horizontal well at the top of the reservoir to contact and mobilize oil by dilution. The diluted oil is produced by a horizontal well. laterally separated from the injector. and located at the bottom of the reservoir. With this configuration. practical production rates can be achieved without appreciable gas bypass. Solvent is separated easily from the produced liquid by distillation and recycled and this results in relatively low net solvent requirements. Gas fills the vacated pores.
The objective of the experiments was to develop process conditions to give high oil production rates with economic solvent requirements. To achieve this major parameters affecting the Vapex performance were investigated: temperature, pressure. solvent injection rates, types of solvent. mixed solvents, well spacing and configurations etc.. The major finding has been that wider lateral well spacings allow higher production rates and make the process more economic. Experimental results indicate that. under suitable conditions. the net solvent injection is about 0.2 B per B of produced oil and that high recoveries and practical rates are achievable. For example. a field prediction based on the experimental data indicates an average oil production rate of450 BID per horizontal well pair. 1000 m long. drilled in a pressure depleted. heavy-oil reservoir that is 10 m thick, to give a recovery of over 50% OOIP for a 70 acre pattern.
The concept of Vapex evolves from the Steam Assisted Gravity Drainage (SAGD) process in which two closely spaced horizontal wells are employed with steam injected from an upper horizontal injector to form a steam chamber in the formation and heated oil drains downwards, driven by gravity, to a horizontal producer located near the base of reservoir. Another form of the process involves the use of multiple vertical injection wells instead of the horizontal injector. In the Vapex process, light hydrocarbon vapours or their mixtures with non-condensible gases are employed instead of steam to extract heavy oil or bitumen from the formation. Compared to thermal processes, the Vapex process can be operated at reservoir temperature with almost no heat loss. Vapex can be used as an alternative to recovery the heavy oil and bitumen from reservoirs which are not suitable for thermal processes such as reservoirs with bottom water and/or high water saturation, vertical fractures, low porosity and low thermal conductivity.