The normal primary source of crude (unrefined) oil is a well that is bored from a surface wellhead into an underground reservoir, which may be under land or sea. Oil is'produced' (taken from an underground reservoir via a well) either as substantially water-free oil, or as an oil/water mixture, and some reservoirs alternatively or additionally produce hydrocarbons as gas, or as gas/oil mixtures. The hydrocarbon gas, or the gaseous hydrocarbon component of a gas/oil mixture, may be at a combination of temperature and pressure that result in at least partial liquefaction of the hydrocarbon gas or gaseous hydrocarbon component, and liquefied natural hydrocarbon gases are herein referred to as'condensate' (or'condensates').

Condensate (s) revert to a gaseous state upon a suitable increase in temperature and/or a suitable decrease in pressure. (Some reservoirs produce non-hydrocarbon gases, e'. g. carbon dioxide, sulphur oxides, hydrogen sulphide, and/or nitrogen oxides, but such gases are generally reckoned to be commercially worthless since they are not fuel hydrocarbons but rather they are contaminants of fuel hydrocarbons and of the environment; accordingly produced non-hydrocarbon gases are not contemplated as being concerned in the present invention).

Where the produced oil is heavy oil (i. e. where the oil molecules include a relatively high number of carbon atoms per molecule), the oil is relatively thick and has a relatively high density together with a relatively high viscosity. The high viscosity of heavy crude oil and of associated oil/water emulsions, combined with the high density of the heavy oil, give rise to problems in transport of the oil from reservoir to final point of sale. The rate of production from a given well bore is dependent upon reservoir conditions. When the hydrostatic pressure within the well bore exceeds the reservoir pressure, the natural flow of liquids from the well may cease. When flowing through the well bore from the reservoir to the surface, the high viscosity of heavy oil

and/or associated emulsions causes substantial hydraulic losses within the tubing that conventionally lines the well bore, and these losses limit the production rate of the well. Tubing diameters can be increased in order to limit pressure losses, and thus to improve production rates, but at substantial extra cost. Alternatively, artificial lift devices can be employed, e. g. gas lift equipment or downhole pumps. However, such artificial lift devices incur high capital expenditure and high operating costs, take up valuable space within the wellhead facilities, can require extensive maintenance, and be unreliable.

Hydraulic losses resulting from the high viscosity of heavy oil also affect the infrastructure required to transport the oil and its derivatives from a marine wellhead to a final point of sale. If required, seabed pipelines of large diameter can be installed in conjunction with large export pumping facilities as a means of continuously transporting heavy oil. As an alternative, a floating storage unit can be moored adjacent to a marine oil well (or, more usually, adjacent to a cluster of marine oil wells), the floating storage unit receiving produced oil from the wells, and intermittently transferring accumulated oil to marine tankers for batch transport of the oil to a land-based facility. However, both pipeline transport of oil and tanker transport of oil incur high capital and operating expenditure. Large export pumping facilities also increase the consumption of energy at the marine wellhead (e. g. a platform mounted on the seabed), and such energy consumption usually requires the combustion of hydrocarbon fuels which results in the emission of environmentally harmful combustion products.

Where heavy crude oil is mixed with water, the high viscosity and high density of the heavy oil make water separation difficult. Extended residence times for water separation in separation equipment for separating oil from water imply that the separation equipment is correspondingly large, with the separation equipment having a consequentially high capital cost. Heating of heavy crude oil to reduce its viscosity and density can aid separation, but incurs adverse effects of capital cost, energy consumption and consequential environmental pollution. Oil/water mixtures may be chemically treated to improve the separation of oil and water, by means of coalescing water droplets or coalescing oil droplets, and thereby increasing settling velocities,

but large quantities of chemicals are necessary with consequent high operating costs additional to the capital cost of chemical treatment equipment.

Condensate is produced from wells bored into gas condensate reservoirs in gas fields.

Prior to export by pipeline, condensate well fluids require to be treated at the wellhead so as to ensure that export specifications are met with respect to gases and liquids.

Difficulties can arise in meeting the specifications for both gases and liquids in typical produced well fluid streams due to the quantity of mid-range hydrocarbons, i. e. hydrocarbons having from two to four carbon atoms per hydrocarbon molecule. Too many heavy components in the gas stream may lead to a final gas product that is'wet' (i. e. a gas containing excessive amounts of liquid), whereas too many light components in the liquid product stream may cause capacity constraints in the downstream export and onshore treatment systems. It is therefore essential that the more volatile components are removed from produced condensate, and hitherto the requisite removal process has involved low pressure separation of the volatile components followed by compression of the separated gas stream and pumping of the condensate stream to export. Such removal processes have required equipment having a high capital cost.

The commercial values of heavy crude oil and condensate are low in comparison to standard crude oils, due to their compositions. Heavy crude oil is low in its content of lighter hydrocarbons (i. e. hydrocarbons typically having two to five carbon atoms per hydrocarbon molecule), and condensate consists only of light hydrocarbons (i. e. hydrocarbons typically having three to six carbon atoms per hydrocarbon molecule).

It is therefore an object of the invention to provide a process which obviates or mitigates these problems associated with the production, transportation, refining, and product market value of heavy crude oils.

According to a first aspect of the present invention there is provided a process for treating heavy crude oil in a manner tending to reduce the viscosity and/or density of the heavy crude oil in a well bore, the process comprising the step of injecting a liquid into the oil at or near the lower end of the well bore, the liquid being volatile and/or

miscible with the heavy crude oil, whereby the hydrostatic head in the well bore is reduced and hydraulic losses associated with lifting the oil to the wellhead are reduced. The liquid that is volatile and/or miscible with heavy oil is preferably hydrocarbon condensate. A consequence of adopting the process according to the first aspect of the present invention is that the sizes of in-well tubing, export pipelines, and export pumps can be reduced for a given throughput of well fluids; additionally, the resultant lower viscosity of the heavy oil may allow shoreward export by pipeline rather than by a combination of floating storage vessel and marine tanker.

According to a second aspect of the present invention there is provided equipment for carrying out the process according to the first aspect of the invention wherein the viscosity and/or density of produced heavy crude oil in a well bore are reduced, said equipment comprising a source of liquid that is volatile and/or miscible with heavy crude oil, liquid injection means, conduit means coupling said liquid source to said liquid injection means for delivering liquid from said source to said liquid injection means during operation of said equipment, said liquid injection means being mounted to inject said liquid into the heavy crude oil at or near the lower end of the well bore whereby the hydrostatic head in the well bore is reduced and hydraulic losses associated with lifting the oil to the wellhead are reduced. Said source of liquid that is. volatile and/or miscible with heavy crude oil is preferably a source of hydrocarbon condensate.

According to a third aspect of the present invention there is provided a process for reducing the viscosity and/or density of a stream of heavy crude oil at or prior to the entry of the stream to separation means for mutually separating the oil and water also contained in the same stream, the process comprising the step of injecting a liquid into the oil stream at or prior to entry of the stream into said separation means, the liquid being volatile and/or miscible with the heavy oil, whereby the settling velocity of droplets of oil or of water is increased. The liquid that is volatile and/or miscible with heavy oil is preferably hydrocarbon condensate. The liquid may be injected into the oil stream prior to entry of the oil stream into said separation means by injecting said liquid into the oil stream at or adjacent the lower end of a well from which the water- containing stream of heavy oil is produced, whereby the process according to the third

aspect of the present invention is combined with the process according to the first aspect of the present invention.

According to a fourth aspect of the present invention there is provided equipment for carrying out the process according to the third aspect of the present invention wherein the viscosity and/or density of a stream of heavy crude oil are reduced at or prior to the entry of the stream into separation means for mutually separating the oil and water also contained in the same stream, said equipment comprising a source of liquid that is volatile and/or miscible with heavy crude oil, liquid injection means, conduit means coupling said liquid source to said liquid injection means for delivering liquid from said source to said liquid injection means during operation of said equipment, said liquid injection means being mounted to inject said liquid into the heavy crude oil at or prior to the entry of the stream of heavy crude oil to said separation means, whereby the settling velocity of droplets of oil or of water is increased. Said liquid that is volatile and/or miscible with heavy oil is preferably hydrocarbon condensate.

Said liquid injection means may be mounted to inject said liquid into the oil at or adjacent the lower end of a well from which the water-containing stream of heavy oil is produced, whereby the equipment according to the fourth aspect of the present invention is combined with the equipment according to the second aspect of the present invention.

According to fifth aspect of the present invention there is provided a process including mixing a stream of heavy crude oil and produced hydrocarbon condensate at or prior to export of the oil and condensate from a wellhead location, the process comprising the step of injecting the hydrocarbon condensate into the stream of heavy crude oil at or prior to its export, whereby to obviate the requirement for provision of equipment for separately treating oil and condensate prior to export. The hydrocarbon condensate may be injected into the oil stream at or prior to entry of the stream into separation means for separation of the oil from water also contained in the stream, whereby the process according to the fifth aspect of the invention is combined with the process according to a preferred form of the third aspect of the invention. The hydrocarbon condensate may be injected into the oil at or adjacent the lower end of a

well producing the oil, whereby the process according to the fifth aspect of the present invention is combined with the process according to a preferred form of the first aspect of the present invention.

According to a sixth aspect of the present invention there is provided equipment for carrying out the process according to the fifth aspect of the present invention wherein a stream of heavy crude oil and produced hydrocarbon condensate are subjected to a process including mixing at or prior to export of the oil and condensate from a wellhead location, said equipment comprising hydrocarbon condensate injection means, conduit means coupling produced hydrocarbon condensate to said hydrocarbon condensate injection means for delivering hydrocarbon condensate to said hydrocarbon condensate injection means during operation of said equipment, said hydrocarbon condensate injection means being mounted to inject said hydrocarbon condensate into the heavy crude oil at or prior to export of the stream of oil, whereby to obviate the requirement for provision of equipment for separately treating oil and condensate prior to export. Said hydrocarbon condensate injection means may be mounted to inject hydrocarbon condensate into the oil stream at or prior to entry of the stream into separation means for separation of the oil from water also contained in the stream, whereby the equipment according to the sixth aspect of the invention is combined with the equipment according to a preferred form of the fourth aspect of the invention. Said hydrocarbon condensate injection means may be mounted to inject hydrocarbon condensate into the oil at or adjacent the lower end of a well producing the oil, whereby the equipment according to the sixth aspect of the present invention is combined with the equipment according to a preferred form of the second aspect of the present invention.

According to a seventh aspect of the invention, there is provided a process for improving the product market value of a stream of heavy crude oil, the process comprising the step of injecting hydrocarbon condensate into the stream of oil in such proportion as to form a blend wherein the product market value is increased with respect to the product values of the unblended oil stream and condensate. The hydrocarbon condensate may be injected into the oil stream prior to the export of the oil from a wellhead, whereby the process according to the seventh aspect of the

present invention is combined with the process according to the fifth aspect of the present invention. The hydrocarbon condensate may be injected into the oil stream at or prior to entry of the stream into means for separation of the oil from water also contained in the stream, whereby the process according to the seventh aspect of the invention is combined with the process according to a preferred form of the third aspect of the invention. The hydrocarbon condensate may be injected into the oil at or adjacent the lower end of a well producing the oil, whereby the process according to the seventh aspect of the present invention is combined with the process according to a preferred form of the first aspect of the present invention.

According to an eighth aspect of the present invention there is provided equipment for carrying out the process according to the seventh aspect of the present invention wherein the product market value of a stream of heavy crude oil is improved, said equipment comprising a source of hydrocarbon condensate, hydrocarbon condensate injection means, conduit means coupling said source of hydrocarbon condensate to said hydrocarbon condensate injection means for delivering hydrocarbon condensate to said hydrocarbon condensate injection means during operation of said equipment, said hydrocarbon condensate injection means being mounted to inject said hydrocarbon condensate into the heavy crude oil in such proportion as to form a blend wherein the product market value is increased with respect to the product market values of the unblended oil stream and condensate. Said hydrocarbon condensate injection means maybe mounted to inject hydrocarbon condensate into the heavy crude oil stream prior to the export of the oil from a wellhead, whereby the equipment according to the eighth aspect of the present invention is combined with the equipment according to the sixth aspect of the present invention. The hydrocarbon condensate injection means may be mounted so as to inject the hydrocarbon condensate into the oil stream prior to entry of the oil stream into means for separation of the oil from water also contained in the stream, whereby the equipment according to the eighth aspect of the invention is combined with the equipment according to a preferred form of the fourth aspect of the invention. The hydrocarbon condensate injection means may be mounted to inject the hydrocarbon condensate into the oil at or adjacent the lower end of a well producing the oil, whereby the equipment according to the eighth aspect of the present invention is combined with

the equipment according to a preferred form of the second aspect of the present invention.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawing wherein sole figure is a schematic diagram of equipment for processing oil, and of procedures for operating the equipment to process oil.

Referring to the drawing, the sole Figure of the drawing schematically illustrates an oil production facility 10 comprising a well 12 together with wellhead equipment 14 serving the well 12 and its produced output. The well 12 is bored into an underground reservoir 16 of heavy oil. The bore of the well 12 is lined in known manner with casing 18 which is internally fitted in known manner with stepped- diameter tubing 20.

A hydocarbon condensate source 22 is linked by a small-bore conduit 24 to a hydrocarbon condensate injection means in the form of a condensate injector 26 mounted at or adjacent the lower end of the well 12 (i. e. at or adjacent the end of the well 12 that has penetrated the reservoir 16). The small-bore conduit 24 can be coiled. tubing (known per se), which is particularly suitable for retro-conversion of a pre- existing oil well to carry out the oil treatment processes of the present invention. The conduit 24 can, however, take any other suitable form, e. g. rigid tubing forming part of a permanent in-well installation. As shown in the schematic drawing, the conduit 24 is located within the tubing 20, but in suitable circumstances, the conduit 24 could be located in the annulus between the tubing 20 and the casing 18, provided the condensate injector was mounted at a location which permitted condensate to be injected into oil at or adjacent the lower end of the well 12.

The condensate source 22 can be any suitable local source of hydrocarbon condensate (e. g. surplus hydrocarbon condensate that is recycled from later stages of the oil treatment processes that take place in the wellhead equipment 14 as will subsequently be detailed), but in a preferred mode of carrying out the invention, the condensate source 22 is a temporary storage tank receiving hydrocarbon condensate from a

gas/condensate production facility (not shown) that may, for example, be a further well (not shown) producing hydrocarbon condensate, or producing hydrocarbon gas that is pressurised and/or cooled until liquefied. The exact means of providing condensate to the source 22 will normally be selected to optimise the capital costs and operating expenditure involved in sourcing, treating, and transporting the condensate to the wellhead equipment 14. Such costs and expenditure will depend, in turn, upon the operating conditions and configurations of both the gas/condensate production facility and the oil production facility 10.

Heavy crude oil (not separately depicted) that was originally held in the geological material of the reservoir 16 flows under the influence of inherent natural forces into the lower end of the tubing 20 to constitute produced oil; such oil may be mixed with water also present in the reservoir 16 so as to form an oil/water mixture that constitutes the produced well fluid. (The water may have been naturally present in the reservoir 16, or the water may have been injected into the reservoir through one or more other wells (not shown) in order to encourage the flow of oil into the well 12.) In operation of the facility 10, condensate from the source 22 is transferred through the conduit 24 to the condensate injector 26 which injects the transferred condensate ihto the oil at or adjacent the lower end of the tubing 20. As the oil and condensate intermingle, the relatively lighter condensate mixes with the relatively heavier oil with the consequence that both the viscosity and density of the combined stream 28 become lower than the viscosity and density of unmixed heavy crude oil. As the combined stream 28 ascends the well 12 towards the surface above the well 12, at least some of the injected condensate will tend to volatilise, in dependence upon the local conditions for vapour/liquid equilibrium. Consequential upon volatilisation, gas breakout will further reduce the bulk density of the fluid stream 28 rising up the well 12. This reduction in static pressure and fluid viscosity will have the effect of increasing the upflow of well fluids through the tubing 20.

Immediately above the well 12, the stream 28 of mixed oil and condensate is passed through a choke control valve 30 that serves to control the flow rate of fluids produced from the well 12. After passing through the choke valve 30, the stream of oil/condensate mixture (or of oil/water/condensate mixture) is passed along choke

outlet line 32 and then fed into a first-stage separator 34 that constitutes part of a separation means for mutually separating the oil and water also contained in the same stream. In the separator 34, evaporated condensate is separated from the inflowing stream as gas and discharged via first-stage separator outlet 36. (Non-evaporated <BR> <BR> condensate remains in the oil, for a purpose detailed below. ) If any water is present in the stream flowing through the line 32, such water is also separated from the inflowing mixture and discharged via first-stage separator outlet 38. Due to the injected condensate having reduced the viscosity of the oil or oil/water mixture produced from the well 12 and fed to the first-stage separator 34, the process of water separation is much improved over conventional water separation processes (wherein condensate injection is not utilised), and the produced well fluids need not require either heating or chemical treatment for effective separation of water. Separated water is taken from the first-stage separator outlet 38 by way of a flow-controlling valve 40 and dispatched via discharge line 42 to equipment (not shown) for treating produced water (i. e. equipment for purifying water produced from a well until the water is sufficiently clean for re-use or for discharge into the environment). Separated gas is taken from the first-stage separator outlet 36 and dispatched for conditioning and/or compression in suitable equipment (not shown). Re-liquefied gas can be recycled to the condensate source 22.

The stream of dewatered/degassed oil/condensate mixture is discharged from the first- stage separator 34 by way of a first-stage separator outlet 44 and a flow control valve 46 to the inlet 48 of a second-stage separator 50 wherein further separation of gas and water (if any) takes place in like manner to the separation process that took place in the first-stage separator 34. (The second-stage separator 50 constitutes another part of a separation means for mutually separating the oil and water also contained in the same stream. ) Gas separated in the second-stage separator 50 is discharged via second-stage separator outlet 52, either to the same gas-processing equipment as gas from the first-stage separator outlet 36, or to any other suitable destination. Re- liquefied gas can be recycled to the condensate source 22. (Non-evaporated <BR> <BR> condensate remains in the oil stream, for a purpose to be detailed below. ) Similarly, any water separated in the second-stage separator 50 is discharged via second-stage separator outlet 54, flow-controlling valve 56 and discharge line 58, either to the same

water-processing equipment as water from the first-stage separator 34, or to any other suitable destination.

It is to be particularly noted that neither the first-stage separator 34 nor the second- stage separator 50 remove all of the condensate that was injected by the injector 26 into the produced oil in the well 12.

Heavy oil is dewatered in the second-stage separator 50 to an extent that meets the specification for export from the facility 10. The stream of dewatered heavy oil is discharged from a second-stage separator 50 outlet 60 to an export pump 62 which boosts the oil pressure to an extent sufficient to propel the oil along an export pipeline 64 and out of the facility 10 to a predetermined destination (not shown) which may, for example, be an on-shore oil storage and refining plant. A valve 66 enables mutual isolation of the facility 10 and the export pipeline 64 when required. Since the viscosity of the stream of oil leaving the second-stage separator 50 has been reduced by the condensate remaining in the oil, oil can readily be exported from the facility 10 without undue consumption of energy by the pump 62 because of hydraulic losses that would be excessive without viscosity reduction, and without the pump 62 or the export line 64 being unduly large.

The stream of oil/condensate mixture in the export pipeline 64 contains a full range of hydrocarbons, and therefore has a product market value that is greater than the sum of the individual product market values of unmixed heavy crude oil and condensate, even before considering the other economic benefits (detailed above) that arise from mixing of oil and condensate. The proportion of condensate to oil in the stream of exported oil/condensate mixture can be adjusted as required to meet operating requirements and/or product market value specifications, e. g. of purchasers. The proportion of condensate to oil can be controllably varied by controllably varying the rate at which condensate is injected into produced oil in the well 12, and/or by controllably varying the internal operating parameters of either or both of the separators 34 and 50.

The benefits of condensate injection have been provided in all the in-well and wellhead processes detailed above by means of condensate injection at or adjacent the lower end of the well 12, but benefits can be obtained in fewer than all these processes by injecting condensate at one or more points downstream of the well 12, e. g. at the first-stage separator inlet 32 and/or at the second-stage separator inlet 48, and/or at the line 62 feeding the inlet of the pump 62, or even (for product market value improvement only) at the end of the export pipeline 64 within the facility 10.

Where appropriate, condensate can be substituted by any other suitable liquid that is volatile and/or miscible with heavy crude oil.

Other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended claims.