WO2015118444A1 - Method for the simultaneous re-injection, without compressors, of low-pressure gas and water into partially exhausted reservoirs with the generation of electric energy by the re-pressurized gas - Google Patents

Method for the simultaneous re-injection, without compressors, of low-pressure gas and water into partially exhausted reservoirs with the generation of electric energy by the re-pressurized gas Download PDF

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Publication number
WO2015118444A1
WO2015118444A1 PCT/IB2015/050814 IB2015050814W WO2015118444A1 WO 2015118444 A1 WO2015118444 A1 WO 2015118444A1 IB 2015050814 W IB2015050814 W IB 2015050814W WO 2015118444 A1 WO2015118444 A1 WO 2015118444A1
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WO
WIPO (PCT)
Prior art keywords
gas
low
water
associated gas
injection
Prior art date
Application number
PCT/IB2015/050814
Other languages
French (fr)
Inventor
Giambattista De Ghetto
Original Assignee
Eni S.P.A.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eni S.P.A. filed Critical Eni S.P.A.
Publication of WO2015118444A1 publication Critical patent/WO2015118444A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • E21B43/166—Injecting a gaseous medium; Injecting a gaseous medium and a liquid medium
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • E21B43/18—Repressuring or vacuum methods

Definitions

  • the present invention relates to a method for the re-injection and use of gas associated with the production of oil in partially exhausted or depleted reservoirs, that can be particularly but not exclusively used in the oil industry.
  • a reservoir is considered partially exhausted or depleted when the pressure inside the reservoir is lower than its initial value.
  • the extraction of crude oil from a reservoir is done through production plants which normally comprise a plurality of wells drilled in the reservoir.
  • the extraction of crude oil is always accompanied by the production of water, which is generally collected in tanks and subsequently disposed of with known technologies, and by the so-called associated gas, i.e. gas dissolved in the oil which separates once it rises to the surface.
  • Said associated gas generally contains methane, ethane, butane and other hydrocarbons and small fractions of inerts.
  • the gas thus produced can be treated in order to obtain gas suitable for being introduced into gas pipelines or for feeding turbines for the generation of electric energy.
  • the turbines are generally combustion turbines, but at times can also be expansion turbines.
  • Part of the associated gas produced is also normally used for the energy consumption of the production plant.
  • the associated gas exits at pressures which are sufficiently high for its entry, without re ⁇ compression, into the pipelines. During its productive life, however, the reservoir becomes depleted, and consequently the outlet pressure of the associated gas drops down to values lower than 20 bar.
  • the gas cannot normally be introduced into the pipelines and, except for the portion used for the energy consumption of the plant, the remaining fraction of associated gas is generally sent to a torch to be burnt.
  • Torches contribute to increasing the pollution rate in the areas where the production plants are present, also representing a waste of resources, as the energy associated with the combustion of the gas is not utilized.
  • compressors are normally installed, which re- pressurize the gas. Once a sufficiently high pressure has been reached, the gas can be re-injected into the reservoir to favour the additional recovery of residual oil or introduced into the pipelines.
  • Compressors however, often require long installation times, they are bulky and costly machines and require continuous maintenance. Considering the fact that the sites where they are installed are often difficult to reach, the maintenance and transport costs are very high.
  • An objective of the present invention is to overcome the drawbacks mentioned above and propose a method for the re-injection and utilization of low- pressure associated gas in depleted reservoirs whose implementation is less costly with respect to known methods .
  • FIG. 1 is a schematic representation of a production plant associated with a reservoir to which a system for the re-injection and use of low-pressure associated gas is applied, according to a first embodiment of the present invention
  • figure 2 is a schematic representation of a production plant associated with a reservoir to which a system for the re-injection and use of low-pressure associated gas is applied, according to a second embodiment of the present invention
  • figure 3 is a schematic representation of a production plant associated with a reservoir to which a system for the re-injection and use of low-pressure associated gas is applied, according to a third embodiment of the present invention.
  • these show a reservoir 10 to which a production plant is associated, comprising a plurality of production wells 11, 12, 13 drilled in the rock formation 14 down to the reservoir 10.
  • the reservoir 10 is, in particular, of the oil type and is normally situated at a depth ranging from 1,000 to 4,000 metres; said reservoir 10 contains oil, associated gas and water.
  • the method for the re-injection and use of low- pressure associated gas comprises the phase in which the low-pressure associated gas, extracted from at least a first extraction well 12 of the above plurality of wells 11, 12, 13, is brought to the inlet of a mixer 21, and the phase in which said low-pressure associated gas is mixed with water at the surface; according to said method, the mixture of associated gas and water is subsequently injected into an injection well 11 of the plurality of wells 11, 12, 13 so as to generate a hydrostatic head which re-pressurizes and conveys the associated gas into said partially exhausted reservoir.
  • the low-pressure gas can therefore be re ⁇ injected without the help of compressors.
  • the necessary pressure is, in fact, supplied by the hydrostatic head which is generated by exploiting the transformation of the potential energy of the water into pressure energy; the greater the depth of the injection well 11, the higher this pressure energy is, and the lower the pressure of the depleted reservoir, the more effective such energy is in pushing the gas.
  • the quantity of water injected into the injection well 11 preferably ranges from 1,000 to 15,000 cubic meters per day.
  • the amount of low-pressure associated gas injected into the injection well 11 is less than 50,000 normal cubic meters per day.
  • the mixer 21 preferably consists of a T-shaped ej ector .
  • the mixing water is preferably the same production water extracted from the reservoir which is collected in tanks 15 and is sent to the mixer 21 through a pump 22.
  • the mixing water is common water mixed with chemical additives so as to be chemically compatible with the reservoir.
  • the re-injected and re-pressurized associated gas is available for being re-produced at a higher pressure than that at which it was produced and is extracted from at least one second extraction well 13 of the plurality of wells 11, 12, 13.
  • the second extraction well 13 is, in particular, separate from the first extraction well 12 from which the low-pressure associated gas exits.
  • At least a part of the re-pressurized gas extracted is sent to a gas turbine 24 for the generation of electric energy. Said electric energy is then stored or distributed according to techniques known per se. In this case, once the gas has passed through the turbine 24, it is decompressed until it returns to pressures lower than 20 bar; the gas leaving the turbine can therefore be re-mixed with water and re-injected into the reservoir 10 to be again re- pressurized and re-used.
  • the re-pressurized gas can be sent to a treatment station 25 to reduce the impurities and make the gas suitable for entering the distribution network.
  • the characteristics of the method, object of the present invention are evident from the above description, as also the relative advantages.
  • the method described in the present invention in fact, allows low-pressure gas to be rapidly and economically re-injected into a depleted reservoir to re-pressurize it, avoiding the use of costly and bulky compressors.
  • the re-injection of associated gas can also be done using the production water deriving from the reservoir itself and consequently will not need to be disposed of with alternative costly methods.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Geology (AREA)
  • Mining & Mineral Resources (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Fluid Mechanics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Jet Pumps And Other Pumps (AREA)

Abstract

Method for the re-injection and use of low-pressure associated gas in a partially exhausted reservoir (10) with which a production plant comprising a plurality of production wells (11,12) is associated, the method comprising the following steps: conveying the low- pressure associated gas extracted from at least one first extraction well (12) of the plurality of wells (11, 12, 13) to the inlet of a mixer (21); mixing the low-pressure associated gas with water at the surface; injecting said mixture of associated gas and water into an injection well (11) selected from the plurality of wells (11, 12) so as to generate a hydrostatic head which re-pressurizes and sends said associated gas into the partially exhausted reservoir.

Description

METHOD FOR THE SIMULTANEOUS RE-INJECTION, WITHOUT COMPRESSORS, OF LOW-PRESSURE GAS AND WATER INTO PARTIALLY EXHAUSTED RESERVOIRS WITH THE GENERATION OF ELECTRIC ENERGY BY THE RE-PRESSURIZED GAS
The present invention relates to a method for the re-injection and use of gas associated with the production of oil in partially exhausted or depleted reservoirs, that can be particularly but not exclusively used in the oil industry.
For the purposes of the present description, a reservoir is considered partially exhausted or depleted when the pressure inside the reservoir is lower than its initial value.
The extraction of crude oil from a reservoir is done through production plants which normally comprise a plurality of wells drilled in the reservoir. The extraction of crude oil is always accompanied by the production of water, which is generally collected in tanks and subsequently disposed of with known technologies, and by the so-called associated gas, i.e. gas dissolved in the oil which separates once it rises to the surface. Said associated gas generally contains methane, ethane, butane and other hydrocarbons and small fractions of inerts.
The gas thus produced can be treated in order to obtain gas suitable for being introduced into gas pipelines or for feeding turbines for the generation of electric energy. The turbines are generally combustion turbines, but at times can also be expansion turbines. Part of the associated gas produced is also normally used for the energy consumption of the production plant. In the first phases of oil extraction, the associated gas exits at pressures which are sufficiently high for its entry, without re¬ compression, into the pipelines. During its productive life, however, the reservoir becomes depleted, and consequently the outlet pressure of the associated gas drops down to values lower than 20 bar.
At these low pressures, the gas cannot normally be introduced into the pipelines and, except for the portion used for the energy consumption of the plant, the remaining fraction of associated gas is generally sent to a torch to be burnt.
Torches, however, contribute to increasing the pollution rate in the areas where the production plants are present, also representing a waste of resources, as the energy associated with the combustion of the gas is not utilized. In order to allow the utilization of low- pressure associated gas, i.e. at pressures lower than 20 bar, compressors are normally installed, which re- pressurize the gas. Once a sufficiently high pressure has been reached, the gas can be re-injected into the reservoir to favour the additional recovery of residual oil or introduced into the pipelines.
Compressors, however, often require long installation times, they are bulky and costly machines and require continuous maintenance. Considering the fact that the sites where they are installed are often difficult to reach, the maintenance and transport costs are very high.
An objective of the present invention is to overcome the drawbacks mentioned above and propose a method for the re-injection and utilization of low- pressure associated gas in depleted reservoirs whose implementation is less costly with respect to known methods .
These and other objectives of the present invention are achieved by providing a method for the re-injection and use of low-pressure associated gas in partially exhausted reservoirs as specified in claim 1.
Further characteristics of the method for the re- injection and use of low-pressure associated gas in partially exhausted reservoirs are object of the dependent claims.
The characteristics and advantages of the method, object of the present invention, will appear even more evident from the following illustrative and non- limiting description, referring to the enclosed schematic drawings, in which:
- figure 1 is a schematic representation of a production plant associated with a reservoir to which a system for the re-injection and use of low-pressure associated gas is applied, according to a first embodiment of the present invention;
figure 2 is a schematic representation of a production plant associated with a reservoir to which a system for the re-injection and use of low-pressure associated gas is applied, according to a second embodiment of the present invention;
figure 3 is a schematic representation of a production plant associated with a reservoir to which a system for the re-injection and use of low-pressure associated gas is applied, according to a third embodiment of the present invention.
With reference to the figures, these show a reservoir 10 to which a production plant is associated, comprising a plurality of production wells 11, 12, 13 drilled in the rock formation 14 down to the reservoir 10.
The reservoir 10 is, in particular, of the oil type and is normally situated at a depth ranging from 1,000 to 4,000 metres; said reservoir 10 contains oil, associated gas and water.
When the wells 11, 12, 13 are put into production, the oil, associated gas and water exit under the thrust of the pressure to which they were subjected in the subsoil. The water extracted from the wells 11, 12 is normally collected in storage tanks 15.
The method for the re-injection and use of low- pressure associated gas according to the present invention comprises the phase in which the low-pressure associated gas, extracted from at least a first extraction well 12 of the above plurality of wells 11, 12, 13, is brought to the inlet of a mixer 21, and the phase in which said low-pressure associated gas is mixed with water at the surface; according to said method, the mixture of associated gas and water is subsequently injected into an injection well 11 of the plurality of wells 11, 12, 13 so as to generate a hydrostatic head which re-pressurizes and conveys the associated gas into said partially exhausted reservoir.
By exploiting the potential energy supplied by the water, the low-pressure gas can therefore be re¬ injected without the help of compressors.
The necessary pressure is, in fact, supplied by the hydrostatic head which is generated by exploiting the transformation of the potential energy of the water into pressure energy; the greater the depth of the injection well 11, the higher this pressure energy is, and the lower the pressure of the depleted reservoir, the more effective such energy is in pushing the gas.
The quantity of water injected into the injection well 11 preferably ranges from 1,000 to 15,000 cubic meters per day.
Preferably, the amount of low-pressure associated gas injected into the injection well 11 is less than 50,000 normal cubic meters per day.
The mixer 21 preferably consists of a T-shaped ej ector . The mixing water is preferably the same production water extracted from the reservoir which is collected in tanks 15 and is sent to the mixer 21 through a pump 22.
Alternatively, the mixing water is common water mixed with chemical additives so as to be chemically compatible with the reservoir.
According to a first embodiment of the present invention, the re-injected and re-pressurized associated gas is available for being re-produced at a higher pressure than that at which it was produced and is extracted from at least one second extraction well 13 of the plurality of wells 11, 12, 13.
The second extraction well 13 is, in particular, separate from the first extraction well 12 from which the low-pressure associated gas exits.
According to a second embodiment of the present invention, at least a part of the re-pressurized gas extracted is sent to a gas turbine 24 for the generation of electric energy. Said electric energy is then stored or distributed according to techniques known per se. In this case, once the gas has passed through the turbine 24, it is decompressed until it returns to pressures lower than 20 bar; the gas leaving the turbine can therefore be re-mixed with water and re-injected into the reservoir 10 to be again re- pressurized and re-used.
According to a third embodiment of the present invention, the re-pressurized gas can be sent to a treatment station 25 to reduce the impurities and make the gas suitable for entering the distribution network.
The characteristics of the method, object of the present invention, are evident from the above description, as also the relative advantages. The method described in the present invention, in fact, allows low-pressure gas to be rapidly and economically re-injected into a depleted reservoir to re-pressurize it, avoiding the use of costly and bulky compressors.
The re-injection of associated gas can also be done using the production water deriving from the reservoir itself and consequently will not need to be disposed of with alternative costly methods.
Finally, the method thus conceived can obviously undergo numerous modifications and variants, all included in the invention; moreover, all the details can be substituted by technically equivalent elements. In practice, the materials used, as also the dimensions, can vary according to technical requirements .

Claims

1. Method for the re-injection and use of low-pressure associated gas in a partially exhausted reservoir (10) with which a production plant comprising a plurality of production wells (11,12,13) is associated, said method comprising the following steps:
conveying the low-pressure associated gas extracted from at least one first extraction well (12) of said plurality of wells (11,12,13) to the inlet of a mixer (21);
mixing at the surface said low-pressure associated gas with water;
injecting said mixture of associated gas and water into an injection well (11) selected from said plurality of wells (11,12,13) so as to generate a hydrostatic head which re- pressurizes and conveys said associated gas into said partially exhausted reservoir.
2. Method according to claim 1 wherein said water is that extracted from said reservoir.
3. Method according to claim 1 or 2 comprising the following step:
extracting said re-pressurized gas from at least one second extraction well (13) of said plurality of wells (11,12,13) .
4. Method according to claim 3 comprising the following step:
sending said extracted re-pressurized gas to the inlet of a gas turbine (24) for the generation of electric power.
5. Method according to claim 3 comprising the following step: sending said extracted re-pressurized gas to the inlet of a treatment station (25) .
6. Method according to one of the previous claims wherein the amount of water injected into said injection well (11) ranges from 1,000 to 15,000 cubic meters per day.
7. Method according to one of the previous claims wherein the amount of low-pressure associated gas injected into said injection well (11) is lower than 50,000 normal cubic meters per day.
PCT/IB2015/050814 2014-02-04 2015-02-03 Method for the simultaneous re-injection, without compressors, of low-pressure gas and water into partially exhausted reservoirs with the generation of electric energy by the re-pressurized gas WO2015118444A1 (en)

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Application Number Priority Date Filing Date Title
ITMI20140162 2014-02-04
ITMI2014A000162 2014-02-04

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2875833A (en) * 1954-02-04 1959-03-03 Oil Recovery Corp Process of recovering oil from oil fields involving the use of critically carbonated water
US6325147B1 (en) * 1999-04-23 2001-12-04 Institut Francais Du Petrole Enhanced oil recovery process with combined injection of an aqueous phase and of at least partially water-miscible gas
WO2003022409A1 (en) * 2001-09-07 2003-03-20 Exxonmobil Upstream Research Company Downhole gas separation method and system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2875833A (en) * 1954-02-04 1959-03-03 Oil Recovery Corp Process of recovering oil from oil fields involving the use of critically carbonated water
US6325147B1 (en) * 1999-04-23 2001-12-04 Institut Francais Du Petrole Enhanced oil recovery process with combined injection of an aqueous phase and of at least partially water-miscible gas
WO2003022409A1 (en) * 2001-09-07 2003-03-20 Exxonmobil Upstream Research Company Downhole gas separation method and system

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