EP0089986B1 - Extraction from oil fields with reinjection of separated materials - Google Patents

Description

The present invention relates to a process intended to maximize the recovery of fluids from liquid hydrocarbon deposits and to facilitate their exploitation with application, in particular, to heavy and / or viscous hydrocarbon deposits, and to hydrocarbon deposits having a high freezing point.

In general, crude oils are made up of a wide variety of hydrocarbons, which can range from methane to heavy parafinics, sometimes mixed, in extremely variable amounts, to cyclic or aromatic hydrocarbons, or even to solids, such as asphaltenes associated with metalloid, metal or other atoms, with possible association of non-hydrocarbon chemicals.

As soon as the graying is a little deep, the exploitation is done by well, and the recovery of the oil in place is a function, more particularly, of the number of wells, their spacings, the speed of withdrawal, and the means used to keep the graying pressure or to move the fluids in place in the deposit towards the withdrawal wells.

As soon as the crude oil in place in the deposit is a little heavy and its viscosity or plasticity is high, the amount of crude oil that we can hope to recover, compared to the amount of oil in place in the deposit, is relatively small. The means to be used to assist production being costly in equipment and in operation.

Furthermore, it often happens that the height of the crude oil column in the production well generates a pressure at the level of the deposit, close to / or greater than the pressure of the deposit. We then have to use pumps of different types to transport, or help transport, the crude oil to the surface, or to produce wells at an acceptable rate. Another method consists in using gas which is remixed with crude oil in the well, in order to decrease the average density of the gas-oil mixture and thus cause or improve the flow rate of the well (gas lift).

In addition, as soon as the oil is too viscous, a heating fluid is injected into the deposit and sometimes, correlatively or not, fluids helping to move the crude oil in the deposit.

Other methods use electrical, electrolytic or high frequency wave processes to obtain the displacement of oil in the deposit.

Finally, another way of proceeding consists in injecting air or an oxidizer in the deposit and causing the combustion of part of the oil in the deposit, and thus benefiting from the effects resulting from this process.

Depending on the type of deposit, these methods, always expensive, give results which are often questionable and sometimes random, and do not always facilitate the separation of effluents returned to the surface.

Thus, from US-A-3 352 355, a washing process at high temperature, alternating and cyclic, is known which is applied to a bituminous shale deposit, after fracturing of said deposit and acidification. But such a method must involve at least three wells to be usable. In addition, it only uses the liquid phase of the effluent. This liquid phase is reheated to very high temperatures before being reinjected into the well in order to provide the deposit with the heat necessary to thin the very viscous oil.

US-A-4008764 relates to a method which consists in injecting gas from an external source, saturated with a solvent, in gaseous form, which also comes from an external source. This process therefore requires at least two sources, which increases operating costs.

Finally, US-A-3,780,805 relates to a process involving a fuel generator which distills the effluent to produce fuel used for equipment. The use of such a fuel generator complicates the installation and makes it more expensive. In addition, the gaseous phase of the effluent does not take place in the production well but in an annex well.

The invention therefore aims to eliminate all or part of the drawbacks or hazards mentioned above.

To this end, the process for producing the hydrocarbon deposit, in particular with the aim of improving the recovery of the effluent, of facilitating its transportation to the treatment installations, as well as its treatment, consists in condensing, at least partly, leaving the production well, after separation of the liquid and gaseous phases, the condensable gases from the effluent, even if they represent only a small percentage of the flow rate of the effluent, and reinjecting the condensate, liquid phase, in the above production well, or possibly the other production wells and / or the deposit.

According to another characteristic of the invention, this process can also comprise, successively, a reheating of the effluent coming from the well, to a temperature favorable to the separation of the liquid and gaseous phases of the effluent if the latter leaves the well at a temperature unfavorable for separation, the separation of the phases of the effluent in at least one separation unit, the compression, the cooling and possibly the dehydration of the gas phase with recovery of the hydrocarbon condensates and the reinjection of the condensates in the liquid phase , in the well or in the deposit.

The invention also relates to an installation for implementing the method according to the invention, this installation comprising at least one well for connecting the river ment to surface installations, at least one effluent heating installation, at least one separator of the gaseous, liquid and solid phases of the effluent, at least one compression-cooling unit allowing partial condensation of the gas phase and optionally a unit for dehydrating the gas phase, with recovery of the hydrocarbon condensates and at least one unit for reinjecting the condensates into the well.

• La figure unique est le schéma-blocs de principe d'une installation pour l'exploitation d'un gisement d'hydrocarbure avec réinjection des fractions légères de l'effluent.

An embodiment of the invention will be described below, by way of nonlimiting example, with reference to the appended drawing in which:

• The single figure is the block diagram of an installation for the exploitation of a hydrocarbon deposit with reinjection of the light fractions of the effluent.

In this drawing, block 1 represents the deposit from which the effluent is withdrawn thanks to the production well represented by block 2. The effluent emanating from this well is reheated in at least one reheating unit 3 at a temperature favorable to separation of the liquid and gas phases and the segregation of the oil, water and possibly solid constituents in at least one separation unit 4. In at least one compression unit 5, the gas phase is then cooled and compressed in one or more stages. In addition, the gas, during this process, is dehydrated to a pink point such that its residual water content does not generate difficulties in the treatment plants located downstream. The condensates collected at various points in unit 5 are recovered and separated from the water associated therewith in a purifier 6 and optionally stored in an auxiliary storage unit 7.

The residual gas recovered at the outlet of unit 5 is then refrigerated in at least one unit 8 using external refrigeration means, at a temperature making it possible to optimize the recovery of light and cold condensates.

At the outlet of the units 8, the light and cold condensates are recovered (block 9) and stored in at least one thermally insulated unit 10.

At the outlet of the units 8, the residual gases are injected into well 2 or into any other well participating in the production of the deposit, directly if their pressure is sufficient, or via at least one additional compression 11 if their pressure is insufficient to be reinjected at the optimum depth provided in the well or wells, or directly in the deposit 1.

Depending on the type and conditions of deposit 1 envisaged, one or the other or the two units 8 and 11 will not necessarily be installed, all or part of the gases being either sold or used to meet energy or operating or detection fluid, field installations.

The condensates recovered in the purifier 6 are then injected into well 2 or into any other well participating in the production of the deposit, directly if their pressure is sufficient, or via at least one pump if their pressure is insufficient to be reinjected at the optimum depth provided in the / or wells, or directly in the deposit.

The cold condensates recovered by the units 9 are then injected, mixed or not mixed in whole or in part with the condensates recovered by the purifier 6, after pumping and reheating (block 13), to satisfy the pressure conditions provided for the injection of the condensates recovered by the purifier 6.

Even if the hydrocarbons naturally found in the deposit have only a weak cut in gas and in parts which can be condensed by the means described above, provided that the installations described above do not cause any loss of substance exceeding the top-up caused by the mother production, a virgin hydrocarbon / recycled light hydrocarbon mixture is created in the / or wells 2 or in the deposit 1, the light hydrocarbon content of which will increase over time.

It thus establishes a growing steering wheel of condensates and gas. As soon as the flow rate from / or wells 2 reaches the desired level, the excess light hydrocarbons can then be injected into one or more wells which can thus be put into production or which will be used to sweep the hydrocarbons in place towards / or producing wells and reinforcing the pressure of the deposit (s). This surplus of condensable hydrocarbons may also be remixed in variable proportions to the crude marketed in order to improve its characteristics or value, or else be marketed directly.

The start-up of the first wells 2 may possibly be carried out by a charge of light hydrocarbons (block 14), condensed or not, coming from a source external to the wells. The water associated with production, and separated by units 4 and 5 can be eliminated on the surface (block 15), but if this water generates pollution or a gene in the environment, it will be after skimming of the residual oil. (block 16), reinjected into / or the deposits 1, in order to maintain the pressure thereof to a certain extent. This residual water can be associated with adjuvants (block 17) modifying its viscosity or causing a swelling effect of the admixture mixture, to move the hydrocarbons in place in the / or the deposits towards the / or producing wells.

An advantage of the process according to the invention consists in that by reinjecting into the / or the production wells or directly into the / or the deposits of light, liquid and / or gaseous hydrocarbons, jointly or not, originating from the / or well, with possible external contribution to facilitate certain operations such as starting production of the well (s), a weight reduction effect of the column of fluid in the well (s) is obtained as well as a reduction which can be considerable of the viscosity of the effluent, this in order to improve the produc activity of the well (s) and reduce the difficulties in separating the phases constituting the natural effluent from the wells.

The injection into the deposit of excess light hydrocarbons, gaseous or not, produced by the deposit will contribute to increase the recovery of hydrocarbons from the deposit by washing the matrix (reservoir rock), decrease in density, the viscosity or plasticity of native hydrocarbons, without generating incompatibility problems such as those which can be created by the addition of fluids foreign to the deposit.

Even if the content of light hydrocarbons in the natural effluent of the deposit is low, after a more or less long period of time, a flywheel is created which ensures regular flow from / or the wells, by recycling permanent.

Even if the facilities described above are relatively high cost, they allow, for certain conditions of isolation of fields, a significant saving, compared to the supply of foreign fluids.

Claims (6)

1. A process for the production of a hydrocarbon field, in particular for the purpose of improving recovery of the effluent and facilitating the transfer thereof to the treatment installations and the treatment thereof, characterised in that it comprises condensing, at least in part, the condensable gases of the effluent, when they leave the production well, after separation of the liquid and gaseous phases, even if such gases represent only a small percentage of the effluent flow, and re-injecting the condensate, in liquid phase, into said production well or possibly other production wells and/orthe field.

2. A process according to claim 1 characterised in that it comprises successively heating the effluent (block 3) from the well to a temperature which is favourable to separation of the liquid and gaseous phases of the effluent if the latter issues from the well at a temperature which is unfavourable to separation, separation of the phases of the effluent in at least one separation unit (block 4), compression, cooling and possibly dehydration of the gaseous phase (block 5), with recovery of the hydrocarbon condensates (block 8) and re-injection of the condensates in liquid phase into the well (2) or into the field.

3. A process according to claim 2 characterised in that it further comprises treatment of the oily water resulting from separation of the gaseous, liquid and solid phases of the effluent (block 4) and treatment of the water which is accidentally oily or polluted by condensates from dehydration of the gaseous phase (block 5) so as to skim off the oil and the residual condensates of the water.

4. A process according to one of the preceding claims characterised in that it further comprises refrigeration of the residual gases (block 8) from compression, cooling and possible dehydration of the gaseous phase (block 5), recovery of the cold condensates from said refrigeration step (block 9) and injection, after optional heating (block 13), into the well or wells (2) and/or the field (1

5. A process according to one of the preceding claims characterised in that it further comprises complementary compression of the residual gases (block 11) remaining after refrigeration of the residual gases (block 8) and injection of said residual gases into the wells (2) and/or the field (1).

6. A production installation for carrying out the process according to one of the preceding claims characterised in that it comprises at least one well permitting the field to be connected to the surface installations, at least one installation for heating the effluent, at least one separator for the gaseous, liquid and solid phases of the effluent, at least one compression-cooling unit for producing partial condensation of the gaseous phase and possibly a unit for dehydration of the gaseous phase, with recovery of the hydrocarbon condensates, and at least one unit for re-injecting the condensates into the well.

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