The present invention relates to the re-boiling of production fluids, in particular in relation to the thermal recovery of heavy oils and bitumen from an oil reservoir.

Reservoir heating is essential in heavy oil (HO) and bitumen recovery. It is known in the art to recover heavy oils and bitumen from an oil reservoir by various thermal recovery processes. Steam assisted gravity drainage (SAGD) is a proven technique for this purpose which uses a pair of horizontal wells drilled into a formation, approximately 4-6 metres apart. The top, or upper, well forms an injection well for introducing steam, optionally mixed with solvents, to create a steam chamber in the formation. The steam flows towards the perimeter of the steam chamber and condenses. The heat from the steam is transferred by thermal conduction to the surrounding reservoir. The heat reduces the viscosity of the heavy crude oil and bitumen in the chamber allowing it to flow to the lower well, known as the production well, where it is pumped to the surface.

Other approaches include Expanding Solvent SAGD (ES-SAGD) developed by Nasr et al (JCPT, Jan 2003, Vol. 2, No. 1) which co-injects a hydrocarbon additive with the steam at low concentrations, and the injection of solvent and steam, the aim being to improve the reduction in viscosity of the bitumen whilst minimising the amount of steam utilised in the process. Another process developed by N-Solv Corporation injects heated solvent without steam. All these thermal recovery processes vary in efficiency. Improvements in the economics of the processes are continuously being investigated, for example to increase the flow of heavy oils and bitumen to the production well whilst using less steam and/or energy.

It is an aim of the present invention to provide a process for enhanced thermal recovery of heavy oils and bitumen from an oil reservoir.

A further aim of the present invention is to provide a process for producing an even distribution of vapour between a pair of horizontal wells.

According to a first aspect of the present invention, there is provided a process for the recovery of viscous hydrocarbons from a hydrocarbon-bearing formation in which are situated an upper injection well and a lower production well, the process comprising the steps of:

injecting steam and/or one or more solvents into the upper injection well thereby creating a heated chamber within the formation;

mixing of the viscous hydrocarbons and the steam/solvent at the boundary of the chamber so formed, whereby the heated chamber causes a reduction in the viscosity of the hydrocarbons to enable their fluid flow, a mixture of the hydrocarbons and water/solvent draining downwards by gravity and sideways by pressure gradient towards the lower production well; and

producing the hydrocarbons to the surface through the lower production well; the process further comprising electrically heating the lower production well to re- evaporate the steam and/or one or more solvents.

A second aspect of the present invention provides a system for the recovery of viscous hydrocarbons from a hydrocarbon bearing formation, the system comprising: an upper well for injection of steam and/or solvent for the creation of a steam and/or solvent heated chamber within the formation whereby the heated chamber indirectly heats the hydrocarbon formation to cause a reduction in the viscosity of the hydrocarbons to promote their drainage by gravity and pressure gradient;

a lower well for collection of the flow of hydrocarbons and water and/or solvent and producing the hydrocarbons to the surface, the lower well including at least one electric heater for re-boiling the water and/or solvent within the lower well.

The present invention is particularly applicable to steam assisted gravity drainage wherein a heater in the lower production well re-boils the water that collects therein to enhance the steam chamber thereby increasing mobilisation of the viscous hydrocarbons.

To this end, a third aspect of the present invention provides a process for the recovery of viscous hydrocarbons from a hydrocarbon bearing formation in which are situated an upper injection well and a lower production well, the process comprising the steps of:

injecting steam into the upper injection well thereby creating a heated chamber within the formation;

mixing of the viscous hydrocarbons and the steam at the boundary of the chamber so formed, whereby the heated chamber causes a reduction in the viscosity of the hydrocarbons to enable their fluid flow, a mixture of the hydrocarbons and water draining downwards by gravity and sideways by pressure gradient towards the lower production well; and

producing the hydrocarbons to the surface through the lower production well; the process further comprising directly heating the lower production well to re- evaporate the steam for its return to the chamber.

Preferably, one or more electric heaters directly heat the lower production well according to the third aspect of the present invention. However, alternative heating methods may be used in this aspect, such as steam heaters.

More preferably, the lower production well is heated at intervals along its horizontal length. For example, by the provision of multiple individual heaters. Preferably, the heaters are individually controllable.

A fifth aspect of the present invention provides a process for the recovery of viscous hydrocarbons from a hydrocarbon bearing formation in which are situated an upper injection well and a lower production well, the process comprising the steps of: injecting steam and/or one or more solvents into the upper injection well thereby creating a heated chamber within the formation;

mixing of the viscous hydrocarbons and the steam/solvent at the boundary of the chamber so formed, whereby the heated chamber causes a reduction in the viscosity of the hydrocarbons to enable their fluid flow, a mixture of the hydrocarbons and water/solvent draining downwards by gravity and sideways by pressure gradient towards the lower production well; and

producing the hydrocarbons to the surface through the lower production well; the process further comprising electrically heating discrete sections of the lower production well to re-evaporate the steam and/or one or more solvents, the electrical heating of the discrete sections being independently controllable.

A sixth aspect of the present invention provides a system for the recovery of viscous hydrocarbons from a hydrocarbon bearing formation, the system comprising: an upper well for injection of steam and/or solvent for the creation of a steam and/or solvent heated chamber within the formation whereby the heated chamber indirectly heats the hydrocarbon formation to cause a reduction in the viscosity of the hydrocarbons to promote their drainage by gravity and pressure gradient;

a lower well for collection of the flow of hydrocarbons and water and/or solvent and producing the hydrocarbons to the surface, the lower well including multiple spaced apart electric heaters for re-boiling the water and/or solvent within the lower well, each electric heater being independently controllable.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example only, to the accompanying drawings, in which:

Figure 1 is a schematic diagram illustrating the flow and chamber patterns in a dual horizontal well without an electric heater;

Figure 2 is a schematic diagram illustrating the flow and chamber patterns in a dual horizontal well according to one embodiment of the present invention, the production well being provided with an electric heater therein;

Figure 3 illustrates in further detail the fluid flow patterns along and across the horizontal well of Figure 2;

Figure 4 is a schematic diagram illustrating the uneven chamber development in a dual horizontal well enhanced oil recovery process; and

Figure 5 is a schematic diagram illustrating an even chamber development by means of selective heating of the chamber according to a further embodiment of the present invention.

Steam and/or solvent enhanced oil recovery (EOR) processes conventionally rely on heated solvent and/or steam being injected through the top, or upper, horizontal well 2 which then heats the surrounding formation to produce a steam/solvent chamber 4, as shown in Figure 1. The heat reduces the viscosity of the heavy oil and bitumen in the formation enabling it to flow by gravity to the production well 6 where it is pumped to the surface. The vapour flow is illustrated by the white arrows in Figures 1 and 2, with the flow of liquid (oil/bitumen, water and/or solvent) being illustrated by the dark arrows.

The present invention provides one or more electric heaters 8 within the production well 6, as shown in Figure 2. The heater effectively re-boils the solvent and/or water from the flowing water/bitumen/HO or water/solvent/bitumen/HO mixtures to enhance recovery of bitumen and HO from the chamber and to recycle the steam/solvent thereby reducing the processing of steam, produced water and/or solvent at the surface, improving the efficiency of the process and optimizing reservoir sweeping. The re-boiled solvent and/or water are returned to the chamber to drive the recovery process. It is clear that the re-evaporation of the production liquids using the electric heater reduces the amount of steam and/or solvent that is required to be injected into the injection well.

Figure 3 illustrates the fluid flow patterns in the vicinity of the horizontal production well 6 in further detail. The electric heater 8 is positioned towards the base of the well 6 causing vaporisation of water and/or solvent that has flowed into the well from the reservoir 12. The vapour then flows from the wellbore back to the reservoir 12 to recycle the steam and further reduce the viscosity of the bitumen and HO thereby increasing their recovery.

Additionally, it is commonplace to experience uneven chamber development in the dual horizontal well EOR processes of the prior art, as illustrated in Figure 4. Often this occurs due to there being variable spacing between the injection well 2 and the production well 6. As shown in Figure 4, there is an intermediate region along the horizontal wells that has no, or minimal, release of injected vapours 10 into the surrounding formation. The electric heater or heaters 8 may be positioned in a well to create an even flow of vapours above the horizontal wells, as illustrated in Figure 5. In a preferred embodiment of the present invention, multiple individually controlled electric heaters are provided along the entire horizontal section of the production well. Any number and arrangement of heaters may be turned on at any particular stage of the process to provide for even chamber development. Furthermore, the amount of heat produced by the heaters may be controlled depending upon the temperature of that region of the well, for example, a poorly heated horizontal well section may be provided with a higher heat rate compared with a well heated section further along the well.

The process of the present invention is particularly applicable to steam assisted gravity drainage or other steam injection recovery processes. The electric heaters within the production wells generate a steam reflux from the production fluid containing hydrocarbons and water, thereby enhancing the steam chamber and recycling of the water. The production well should ideally be of a large diameter, for example, 8 5/8" (219mm) or larger, to maximise segregation of the vapour and fluid flows in the production well. It should also have a large flow area on the well screen surface to minimise turbulence and avoid pressure build up in the wellbore. It is envisaged that the heater will be provided within the production well to provide the best results. If a production tubing is used within the production well, it will be necessary to install the heaters outside the tubing.