PROCESS OF PREPARING A GAS COMPOSITION AND USE THEREOF

Abstract: The present invention provides a process of preparing of a gas composition suitable for the injection in an oil-containing field to increase the degree of recovery and simultaneously reduce the discharge of CO2 to the atmosphere. However, injection of a gas composition containing large amounts of oxygen will result in a degraded submarine formation which is not desirable. The present invention relates to a process for the production of a gas composition comprising N2, CO2, minor parts of NOx, VOC (volatile organic compounds) and about 0-2,0 mole % O2 from an oxygen containing exhaust gas, wherein a stream of an exhaust gas from the combustion of air and natural gas in a gas turbine containing 18 % by weight O2 or less, is combusted with natural gas, whereupon the desired gas composition is discharged as a flue gas. Further, a process of recovering oil from submarine formations is also described, where said gas composition is compressed and injected into a submarine formation. The use of previous said gas composition for injection in an oil-containing field for the recovery of oil is also disclosed by the present invention.

Description: Process of preparing a gas composition and use thereof. The present invention relates to a process of preparing a gas composition comprising N 2 , CO 2 , minor parts of NO x , VOC (volatile organic compounds) and about 0-2,0mole% O 2 from an oxygen containing exhaust gas and use thereof. It is well-known to inject CO 2 in submarine formations and oil-containing fields to reduce the discharge of CO 2 to the atmosphere. Injection of CO 2 into oil- containing fields simultaneously increases the recovery of oil from said oil- containing field. Further it is also known to produce electrical power from fossil fuel. Increasing the quantity of oil recovery by water injection, nitrogen and CO 2 separated from a oil/gas mixture is also known in the art. Large quantities of gas is required to recover oil in an oil-containing field by injection of a gas. CO 2 can be obtained by separating CO 2 either from the feed gas or from the flue gas of combustion e.g. a gas power plant. Large amounts of flue gas is required when only the CO 2 content in the flue gas from combustion is used for injection in oil-containing fields to recover oil, since the typical contents of CO 2 is in the magnitude of 3-10mole%. The remainder of the combustible constituents are conveyed forward to the combustion for the production of electrical power by purification of the feed gas ( e.g. upstreams to a gas power plant). The remainder of the constituents are conveyed to the atmosphere by purification of the combustion gas (e.g. downstreams to a gas power plant). Due to the large gas quantities, which is required for the injection in oil-containing fields to increase the recovery of oil, will an inert gas composition mainly consists of CO 2 obtained by the separation of CO 2 from a fuel gas or flue gas in a gas fired power plant , the production of large amounts of electrical power is involved. Said production of electrical power may cause problems concerning sales of electrical power and in particular cases transmission capacity of electrical power. The object of the present invention is to provide a process of preparing a gas composition suitable for the injection in an oil-containing field in such a way to increase the degree of recovery and simultaneously reducing the discharge of CO 2 to the atmosphere. However, injection of a gas composition containing large amounts of oxygen will result in a degraded submarine formation, which is not desirable. The present invention thus provides a process for the production of a gas composition comprising N 2 , CO 2 , minor parts of NO x , VOC (volatile organic compounds) and about 0-2,0mole% O 2 from an oxygen containing exhaust gas, wherein a stream of a exhaust gas from the combustion of air and natural gas in a gas turbine containing 18% by weight O 2 or less, is combusted with natural gas, whereupon the desired gas composition is discharged as a flue gas. The content of O 2 in exhaust gas from the combustion of air and natural gas in a gas turbine is in the magnitude of 12-18% O 2 . The gas composition obtained preferably contains about 0 to 1 ,0mole% O 2 , and more preferably about 0,1-0,5mole% O 2 . The present invention may utilise any exhaust gas from a combustion process, but a preferred embodiment of the invention is the production of an inert gas composition from the combustion products from a gas turbine plant. The present invention also comprise a process of recovering oil from submarine formations wherein a gas composition as mentioned above, comprising N 2 ,CO 2 , minor parts of NO x and VOC (volatile organic compounds), and O 2 is further compressed and injected into said submarine formation. Further, the use of a gas composition comprising N 2 , CO 2 , minor parts of NO x , VOC (volatile organic compounds) and about 0-2,0mole% O 2 from an oxygen containing flue gas for injection in an oil- containing field for the recovery of oil is also disclosed by the present invention. The present invention thus comprises a process of preparing a gas composition where said gas composition contains from 0-1 ,0 mole % O 2 , more preferably from 0,1-0,5mole% O 2 . Previous problems concerning the degradation of oil-containing fields are reduced by said amounts of O 2 which also are to be considered as minor. The process comprises eliminating molecular oxygen of the exhaust gases by charging a metered amount fuel sufficient to combust the remaining amounts of oxygen almost completely (stoichiometric or reaction equivalent combustion) in a steam boiler. Steam is generated into the steam boiler, which is utilised for operating a vapour turbine which further operate an electrical generator. One of the objects of preparing an inert gas composition as described herein, is that said process also address an energy economy aspect. Large amounts of an inert gas composition is also provided by preparing a gas composition from any exhaust gas of a combustion process, not only using CO 2 as an inert gas, but wherein also the remaining components except for O 2 are used. The amount of CO 2 prepared from natural gas constitute only 8-10% of the total gas amounts of the present invention. Combustion of exhaust gas from e.g. a gas turbine plant are produced in stoichiometric amounts, whereby the remaining amounts of O 2 is mainly converted to CO 2 . According to the present invention, a smaller gas turbine plant is thus provided including large amounts of exhaust gas per generated amounts of electric power for the preparation of a desired amount of an inert gas composition. The injection of an inert gas in an oil-containing field provides for the reduction of discharge to the atmosphere of CO 2 from the power plant. The present process can be performed in a processing plant onshore or on an offshore installation e.g. a platform or a barge. The production of electric power according to the present invention on a offshore installation or an oil drilling platform, will provide for a contribution to or a coverage of the power demand. A further advantage of such an offshore installation at oil-containing fields is the possibility of moving it from one field to another. The temperature of the flue gases after this combustion is decided by the exploitation ratio and the dimensioning of the steam boiler. The flue gases are dried and compressed to the desired pressure dependent of the character of the reservoir prior to injection. The invention is described in more detail in the following referring to examples and the enclosed figures. Figure 1 is a flowsheet of a combined gas power plant (CCPP - Combined Cycle Power Plant) comprising a device for afterburning. Air (stream 1) and natural gas (stream 2) is fed to a CCPP, from which an exhaust gas (stream 3) is discharged. One part (in figure 1 shown as 20% of the amount of the exhaust gas from the CCPP (stream 4) ) is then fed to an afterburning device to which also fuel in the form of natural gas (stream 6) is fed. The desired gas composition (stream 8) from the afterburning device is further fed to drying and compression prior to the injection of the gas composition into an oil-containing field for recovering oil. The drying and compression devices are omitted in figure 1. Example 1 : Example 1 elucidate the composition and the amount of natural gas (stream 6) which is conveyed into the afterburning device, shown in table 1 , together with the exhaust gas from the combustion of air and natural gas in a gas turbine (stream 4) , as shown in table 2. Further the composition and amounts of the gas composition produced containing N 2 , CO 2 , minor parts of NO x and VOC (volatile organic compounds), and about 0-2,0mole % O 2 from an oxygen containing exhaust gas (stream 8) is shown in the example. The amounts and the composition of stream 8, which moreover is the desired gas composition, is given in table 3. Table 1 : Table 2: Table 3:

Claims: Claims : 1. A process of preparing a gas composition comprising N 2 , CO 2 , minor parts of NO x and VOC (volatile organic compounds), and about 0-2,0 mole% O 2 from an oxygen containing exhaust gas, wherein a stream of an exhaust gas from the combustion of air and natural gas in a gas turbine containing 18% by weight O 2 or less, is combusted with natural gas, whereupon the desired gas composition is discharged as a flue gas. 2. The process of claim 1 , wherein the gas composition obtained contains about 0 to 1 ,0 mole % O 2 . 3. The process of the claims 1-2, wherein the gas composition obtained preferably contains about 0,1-0,5mole % O 2 . 4. The process of claim 1 , wherein the flue gas from the combustion of air and natural gas is used as combustion products from a gas turbine plant. 5. A process of recovering oil from submarine formations, wherein the gas composition according to one of the claims 1-4 comprising N 2 , CO 2 , minor parts of NO x and VOC (volatile organic compounds), and O 2 is compressed and injected into said submarine formation. 6. The use of a gas composition produced according to claim 1 , for injection in an submarine formation for the recovery of oil.

Inventors: ELVESTAD SIMEN, LIA TORBJOERN A, LONT AUKE, ELVESTAD, SIMEN, LIA, TORBJOERN, A., LONT, AUKE
Applicants: ELVESTAD SIMEN, LIA TORBJOERN A, LONT AUKE, NATURKRAFT AS, ELVESTAD, SIMEN, LIA, TORBJOERN, A., LONT, AUKE
Application year: 1999
Main classification: E21B43
IPC codes: E21B43