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A process for the recovery of hydrocarbons from a hydrocarbon bearing formation having an extraction chamber where the extraction chamber has an extraction surface. The process has the steps of heating a solvent, such as propane, and then placing the solvent into the extraction chamber at a temperat

A process for the recovery of hydrocarbons from a hydrocarbon bearing formation having an extraction chamber where the extraction chamber has an extraction surface. The process has the steps of heating a solvent, such as propane, and then placing the solvent into the extraction chamber at a temperature and a pressure sufficient for the solvent to be in a vapor state in the chamber and to condense on the extraction surface. The next step is to produce a liquid blend of solvent and heavy oil and then to separate the solvent from said heavy oil. Then the solvent is purified, before being re-injected into the formation again. The purification step removes less condensable fractions from the solvent to ensure a purity that is high enough to support continued heat transfer at extraction conditions. The pressure and temperature are set to levels to cause less condensable fractions to drain away with the liquid bitumen and solvent blend that is produced, thus mitigating heat transfer poisoning.

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1. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation having an extraction chamber, said extraction chamber having an extraction surface, the process comprising the steps of:heating a solvent; placing said solvent into said extraction chamber at a temperature end a press

1. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation having an extraction chamber, said extraction chamber having an extraction surface, the process comprising the steps of:heating a solvent; placing said solvent into said extraction chamber at a temperature end a pressure sufficient for said solvent to be in a vapour state in said chamber and to condense on said extraction surface; controlling said extraction temperature and pressure to achieve bubble point conditions to permit continued solvent condensation at the extraction surface; producing a liquid blend including at least solvent and in situ hydrocarbons; separating said solvent and from said in situ hydrocarbons; purifying said solvent; and reusing said purified solvent in said formation. 2. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1 wherein said step of producing said blend of solvent and heavy oil includes producing a liquid blend including liquefied gases other than said solvent combined in the heavy oil.3. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1, wherein said step of purifying said solvent means removing compounds from said solvent having a different dewpoint temperature from said solvent.4. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1, wherein said step of purifying said solvent comprises removing compounds from said solvent having a lower dewpoint temperature from said solvent at the same pressure.5. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1, wherein said step of purifying said solvent comprises removing compounds from said solvent having a higher dewpoint temperature from said solvent at the same pressure.6. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1, wherein said solvent is purified sufficiently so that when combined with compounds released in said formation from said hydrocarbons being recovered which compounds are less condensable than said solvent at the same pressure, the total mole fraction of any less condensable compounds present is less than an amount which lowers the bubble point temperature of a vapour mixture at said extraction surface below a naturally occurring reservoir temperature at a desired extraction pressure.7. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 6 wherein said desired extraction pressure is a pressure at which said less condensable vapours are removed at about the same rate as they arise at the extraction surface.8. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1, wherein said solvent is purified sufficiently so that when combined with less condensable compounds released in said formation from said hydrocarbons being recovered the total mole fraction of any less condensable compounds present is less than 10 mol %.9. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1 wherein said solvent is purified sufficiently so that when combined with less condensable compounds released in said formation from said hydrocarbons being recovered the total mole fraction of any less condensable compounds present is less than 5 mol %.10. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1 wherein said heating step occurs above grade.11. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1 wherein said heating step occurs below grade.12. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1 wherein said formation has a fracture pressure, and said extraction pressure is selected to be between 75% and 100% of said fracture pressure.13. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation as claimed in claim 1 further including the step of adding a volume of make up solvent generally corresponding to the produced volume of hydrocarbon.14. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface, the process comprising the steps of,injecting solvent in a vapour form into said extraction chamber; managing vapour concentrations of compounds other than said condensing solvent present in the extraction chamber to achieve bubble point conditions at the extraction surface to permit effective heat transfer conditions to be established and to permit said solvent vapour to continue to condense on said extraction surface, and recovering a liquid of blend of solvent and hydrocarbon. 15. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation as claimed in claim 14 wherein the step of managing vapour concentrations of compounds other than said condensing solvent further comprises purifying said solvent prior to placing the same in the extraction chamber.16. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation as claimed in claim 14 wherein said step of managing vapour concentrations of compounds other than said condensing solvent comprises maintaining an extraction pressure sufficiently high to remove enough of said other compounds present in said extraction chamber to prevent the same from inhibiting heat transfer from said solvent to said hydrocarbons being recovered.17. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation as claimed in claim 14, wherein said step of managing vapour concentrations of compounds other than said condensing solvent comprises maintaining an extraction temperature sufficiently high to remove enough of said other compounds present in said extraction chamber to prevent the same from inhibiting heat transfer from said solvent to said hydrocarbons being recovered.18. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation as claimed in claim 14 wherein said step of managing vapour concentrations of compounds other than said condensing solvent comprises maintaining an extraction temperature.19. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface, the process comprising the steps of;injecting a solvent into said extraction chamber in a vapour phase; combining said solvent with naturally occurring vapours emitted by said hydrocarbons at extraction temperature and pressure to form a vapour mixture; and managing one or both of an extraction temperature or an extraction pressure to maintain a bubble point temperature of said vapour mixture above a naturally occurring formation temperature during said recovery process wherein maid extraction pressure is maintained at a level sufficient to permit continued condensation of said solvent vapour at said extraction temperature. 20. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface as claimed in claim 19 wherein a predetermined extraction pressure is within 10% of fracture pressure.21. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface as claimed in 19 wherein said step of managing a pressure and a temperature in said extraction chamber includes the step of maintaining an extraction temperature at a predetermined temperature.22. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface as claimed in claim 21 wherein said predetermined extraction temperature is within 10% of a maximum extraction temperature in degrees centigrade for said solvent at formation fracture pressure.23. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface as claimed in claim 19 wherein said step of managing a pressure and a temperature in said extraction chamber includes the step of maintaining a solvent purity at said extraction face by removing said naturally occurring vapours at a rate which is substantially equal to a rate at which the same are emitted.24. A process for injecting a condensing solvent into an underground hydrocarbon bearing formation having an extraction chamber with an extraction surface, the process including the steps of displacing a heated solvent vapour mixture into said extraction chamber at a temperature sufficient for said solvent to flow through the extraction chamber as a vapor and to condense on said extraction surface at an extraction pressure, and maintaining process conditions in said extraction chamber to keep a temperature difference between a bubblepoint temperature and a dewpoint temperature of said mixture at said interface of less than 30C.25. A process for recovering hydrocarbons from an underground formation using a condensing solvent for heat transfer to a bitumen extraction surface, the method comprising:heating said solvent sufficiently for said solvent to flow through an extraction chamber as a vapor and to condense on said bitumen extraction surface at an extraction pressure; and pressurizing said formation to said extraction pressure, wherein said extraction pressure is sufficient to permit less condensable gases present at said bitumen extraction surface to drain away with a produced liquid at a rate to permit continued condensation to occur at said bitumen extraction surface. 26. A process for recovering hydrocarbons from an underground formation using a condensing solvent for heat transfer to a bitumen extraction surface, as claimed in claim 25, including the step of using purified propane as the solvent.27. A process for recovering hydrocarbons from an underground formation using a condensing solvent for heat transfer to a bitumen extraction surface as claimed in claim 25 wherein said step of pressurizing said formation includes the step of pressurizing the formation enough to cause said less condensable gases to drain at a rate equal to the rate at which said gases arise at said extraction surface.28. A process for the recovery of hydrocarbons from a hydrocarbon bearing formation having an extraction chamber, said extraction chamber having an extraction surface, the process comprising the steps of:heating a solvent; placing said solvent into said extraction chamber at a temperature and a pressure sufficient for said solvent to be in a vapour state in said chamber and to condense on said extraction surface and to achieve bubble point conditions at the extraction surface to permit continued solvent condensation at the extraction surface; producing a liquid blend including at least solvent and heavy oil; separating said solvent from said heavy oil; purifying said solvent to an extent sufficient to permit steady state heat transfer at said temperature and pressure; and reusing said purified solvent in said formation.