US20140008064A1

US20140008064A1 - Use of crude glycerol (cg) for production of formulations for mineral oil production and process for producing mineral oil from mineral oil deposits having inhomogeneous permeability

Info

Publication number: US20140008064A1
Application number: US13/933,519
Authority: US
Inventors: Vladimir Stehle; Liubov Altunina; Vladimir Kuvshinov
Original assignee: Wintershall Holding GmbH; Institute of Petroleum Chemistry of Siberian Branch of Russian Academy of Sciences; Institute of Petroleum Chemistry of Siberian Branch of Russian Academy
Current assignee: Wintershall Dea GmbH; Institute of Petroleum Chemistry of Siberian Branch of Russian Academy of Sciences; Institute of Petroleum Chemistry of Siberian Branch of Russian Academy
Priority date: 2012-07-04
Filing date: 2013-07-02
Publication date: 2014-01-09

Abstract

The present invention relates to the use of crude glycerol (CG) as a constituent of a formulation for mineral oil production and to a process for producing mineral oil from mineral oil deposits having inhomogeneous permeability. The inventive use of crude glycerol (CG) makes it possible to modify the rheological properties of the inventive formulations (F) within wide ranges, and makes it possible to adjust them to the geotechnical parameters, the environmental conditions and the nature of the mineral oil in different mineral oil deposits.

Description

This patent application claims the benefit of pending U.S. provisional patent application Ser. No. 61/667,962 filed on Jul. 4, 2012, incorporated in its entirety herein by reference.
The present invention relates to a process for producing mineral oil from mineral oil deposits having inhomogeneous permeability. The inventive use of crude glycerol (CG) makes it possible to modify the rheological properties of the inventive formulations (F) within wide ranges, and makes it possible to adjust them to the geotechnical parameters, the environmental conditions and the nature of the mineral oil in different mineral oil deposits.
In natural mineral oil deposits, mineral oil occurs in cavities of porous reservoir rocks which are closed off from the surface of the earth by impervious overlying strata. In addition to mineral oil, including proportions of natural gas, a deposit further comprises water with a higher or lower salt content. The cavities may be very fine cavities, capillaries, pores or the like, for example those having a diameter of only approx. 1 μm; the formation may additionally also have regions with pores of greater diameter and/or natural fractures, however. In a mineral oil deposit, one or more oil-bearing strata may be present.
After the well has been sunk into the oil-bearing strata, the oil at first flows to the production wells owing to the natural deposit pressure, and erupts from the surface of the earth. This phase of mineral oil production is referred to by the person skilled in the art as primary production. In the case of poor deposit conditions, for example a high oil viscosity, rapidly declining deposit pressure or high flow resistances in the oil-bearing strata, eruptive production rapidly ceases. With primary production, it is possible on average to produce only 2 to 10% of the oil originally present in the deposit.
Mineral oil production is differentiated into primary, secondary and tertiary production.
In order to enhance the yield, what are known as secondary production processes are therefore used. The most commonly used process in secondary mineral oil production is water flooding. This involves injecting water through injection wells into the oil-bearing strata. This artificially increases the deposit pressure and forces the oil out of the injection wells to the production wells. By water flooding, it is possible to substantially increase the yield level under particular conditions.
It is additionally possible to increase the mineral oil yield further by measures of tertiary oil production. In tertiary oil production, suitable chemicals are used as assistants for oil production. This includes what is called “polymer flooding”. Polymer flooding involves injecting an aqueous solution of a thickening polymer into the mineral oil deposit through the injection wells instead of water. These aqueous solutions are also referred to as flooding compositions for tertiary mineral oil production. As a result of the injection of the polymer solution, the mineral oil is forced through said cavities in the formation from the injection well proceeding in the direction of the production well, and the mineral oil is finally produced through the production well. Due to the elevated viscosity of the polymer solution, which is matched to the viscosity of the mineral oil, the polymer solution is thus able to break through cavities at least not as easily as is the case for pure water, if at all. Parts of the deposit not accessible to the water are reached by the polymer solution.
The flooding compositions used for tertiary mineral oil production are aqueous solutions of a multitude of different thickening water-soluble polymers, both synthetic polymers, for example polyacrylamide or copolymers of acrylamide and other monomers, especially monomers having sulfo groups, and polymers of natural origin, for example glucosylglucans, xanthans or diutans.
The above-described polymers, however, are costly, and so the use thereof as a constituent of a flooding composition in tertiary production processes leads to a significant increase in cost of the mineral oil produced.
In the ideal case of water flooding, a water front proceeding from the injection well should force the oil homogeneously over the entire mineral oil formation to the production well. In practice, a mineral oil formation, however, has regions with different levels of flow resistance. In addition to oil-saturated reservoir rocks which have fine porosity and a high flow resistance for water, there also exist regions with low flow resistance for water, for example natural or synthetic fractures or very permeable regions in the reservoir rock. Such permeable regions may also be regions from which oil has already been recovered. In the course of water flooding, the flooding water injected naturally flows principally through flow paths with low flow resistance from the injection well to the production well. The consequences of this are that the oil-saturated deposit regions with fine porosity and high flow resistance are no longer flooded, and that increasingly more water and less mineral oil is produced via the production well. In this context, the person skilled in the art refers to “watering out of production”. The effects mentioned are particularly marked in the case of viscous mineral oils.
For production of mineral oil from deposits with high mineral oil viscosity, the mineral oil can also be heated by injecting steam in the deposit, thus reducing the oil viscosity. As in the case of water flooding, however, steam and steam condensate can also strike undesirably rapidly through high-permeability zones from the injection wells to the production wells, as a result of which the efficiency of the production is reduced.
It is customary at present to conduct both steps when developing deposits containing viscous oil: water flooding followed by steam flooding.
The prior art discloses measures for closing such high-permeability zones between injection wells and production wells by means of suitable measures. As a result of these, high-permeability zones with low flow resistance are blocked and the flooding water or the flooding steam flows again through the oil-saturated, low-permeability strata. Such measures are also known as “conformance control”. An overview of measures for conformance control is given by Borling et al. “Pushing out the oil with Conformance Control” in Oilfield Review (1994), pages 44 ff.
For conformance control, it is possible to use comparatively low-viscosity formulations of particular chemical substances which can be injected easily into the formation, and the viscosity of which rises significantly only after injection into the formation under the conditions which exist in the formation. To enhance the viscosity, such formulations comprise suitable inorganic, organic or polymeric components. The rise in viscosity of the injected formulation can firstly occur with a simple time delay. However, there are also known formulations in which the rise in viscosity is triggered essentially by the temperature rise when the injected formulation is gradually heated to the deposit temperature in the deposit. Formulations whose viscosity rises only under formation conditions are known, for example, as “thermogels” or “delayed gelling systems”. However, these formulations can be employed efficiently only in deposits whose temperature is above 60° C.
SU 1 654 554 A1 discloses processes for producing oil, in which mixtures comprising aluminum chloride or aluminum nitrate, urea and water are injected into the mineral oil formations. At the elevated temperatures in the formation, the urea is hydrolyzed to carbon dioxide and ammonia. The ammonia which forms significantly increases the pH of the water, as a result of which high-viscosity aluminum hydroxide gel precipitates out, which blocks the high-permeability regions.
RU 2 339 803 C2 describes a process for blocking high-permeability regions in mineral oil deposits, in which the volume of the high-permeability region to be blocked is first of all determined. Subsequently, an aqueous formulation comprising carboxymethylcellulose and chromium acetate as a crosslinker is injected into the region to be blocked, the volume of the injected mixture being 15%, based on the total volume of the region to be blocked. In the next step, an aqueous formulation comprising polyacrylamide and a crosslinker is injected.
L. K. Altunina and V. A. Kushinov, Oil & Gas Science and Technology—Rev. IFP, Vol. 63 (2008), pages 37 to 48 and Altunina L. K., Kuvshinov V. A., Stasyeva L. A.//Thermoreversible Polymer Gels for Increased Efficiency of Cyclic-Steam Well Treatment,—2006—1 CD-ROM,—68th EAGE Conference & Exhibition “Opportunities in Marine Areas”, Paper D030 describe various thermogels and the use thereof for oil production, including thermogels based on urea and aluminum salt, and thermogels based on cellulose ethers.
The above-described gel-forming formulations are “thermogels”, i.e. formulations whose viscosity rises with increasing temperature. A disadvantage of these thermogels is that they can be used only in mineral oil deposits which have deposit temperatures of at least 60° C.
It was therefore an object of the present invention to provide a formulation for production of mineral oil which has the above-described disadvantages of the prior art only to a reduced degree, if at all. The formulation is to be suitable for blocking of highly permeable zones in mineral oil deposits having deposit temperatures below 60° C. The formulation is additionally to be suitable as a flooding composition for tertiary mineral oil production. The rheological and physical parameters of the formulation are to be modifiable within wide ranges and to allow efficient profile modification of the flood front.
It was a further object of the present invention to provide a process for producing mineral oil from mineral oil deposits having inhomogeneous permeability using these formulations.
This object is achieved by the process for tertiary production of mineral oil from underground mineral oil deposits having a deposit temperature T_D, into which at least one injection well and at least one production well have been sunk, comprising at least the following process steps:
i) injecting a flooding composition through at least one injection well into the mineral oil deposit, using, as the flooding composition, a formulation (F) having a temperature T_Fhigher than the temperature T_D,
ii) cooling the flooding composition from step i) in the mineral oil deposit and
iii) injecting a further flooding composition through at least one injection well into the mineral oil deposit and withdrawing mineral oil through at least one production well, wherein the formulation (F) comprises crude glycerol (CG) has the following composition:

- 80 to 90% by weight of glycerol,
- 10 to 20% by weight of water,
- 0 to 10% by weight of inorganic salts and
- 0 to 1% by weight of organic compounds,
- where the percentages by weight are each based on the total weight of the crude glycerol (CG).

It has been found that, surprisingly, crude glycerol (CG), which is inexpensive and not of ecological concern, is suitable for production of formulations (F) suitable as flooding compositions for tertiary mineral oil production or as compositions for blocking of highly permeable zones in mineral oil deposits.
The rheological and physical properties of the formulation (F) can be modified and adjusted easily by simple variation of the component concentrations, especially of the concentration of crude glycerol (CG).
It is thus possible to adjust the formulations (F) in a simple manner to the geotechnical parameters and environmental conditions, i.e. more particularly to the deposit temperature and the viscosity of the oil present in the deposit. The inventive formulations (F) are especially suitable for use in mineral oil deposits having relatively low deposit temperatures (cold mineral oil deposits). The use of crude glycerol (CG) allows the rheological and physical properties of the formulation (F) to be varied within wide ranges, such that the formulation (F) can also be used in the development of mineral oil deposits having relatively high deposit temperatures (hot mineral oil deposits). A further advantage of the inventive formulation (F) is that the freezing temperature can also be regulated within wide ranges. By varying the component contents, especially the concentration of crude glycerol (CG), it is possible to significantly reduce the freezing temperature. This enables the use of the formulation (F) in the development of mineral oil deposits in cold regions of the earth too, for example in permafrost regions. The density of the formulation (F) can be adjusted such that it is greater than the density of the deposit water and/or mineral oil which occurs in the mineral oil deposit. It is thus possible to enhance the efficiency of the oil displacement.
In the context of the present invention, cold mineral oil deposits are understood to mean deposits having temperatures<60° C. Hot mineral oil deposits are understood to mean deposits having a temperature of at least 60° C.
The viscosity of the formulations (F) decreases with rising temperature and increases with decreasing temperature. In other words, the formulations (F) have a low viscosity at relatively high temperatures, whereas the viscosity of the formulation (F) rises when the temperature is lowered. The formulation (F) thus differs from the conventional thermogels described in the prior art, where the viscosity rises when the temperature increases. The conventional thermogels have a low viscosity at low temperatures, whereas the viscosity thereof rises significantly with increasing temperature.
Glycerol is a trihydric alcohol ( IUPAC name 1,2,3-propanetriol) having the formula CH₂(OH)—CH(OH)—CH₂(OH). Glycerol is produced by petrochemical means from propene via the allyl chloride and epichlorohydrin intermediates. Crude glycerol (CG) shall be understood in the context of the present invention to mean all mixtures comprising glycerol, water, inorganic salts and organic compounds (other than glycerol). Preference is given, however, to crude glycerol (CG) which is obtained from natural fats or oils. Glycerol is a constituent of all animal and vegetable fats/oils. Crude glycerol (CG) is obtained in large amounts as a by-product of biodiesel production. For production of biodiesel, vegetable oils, for example rapeseed oil, are transesterified with methanol. A fat/oil molecule (triacyl glyceride) is reacted with three methanol molecules to give glycerol and three fatty acid methyl esters. Thus, 10 liters of vegetable oil and 1 liter of methanol give approx. 10 liters of biodiesel and 1 liter of crude glycerol.
Crude glycerol (CG) preferably has the following composition:

- 80 to 90% by weight of glycerol,
- 10 to 20% by weight of water,
- 0 to 10% by weight of inorganic salts and
- 0 to 1% by weight of organic compounds,

where the percentages by weight are each based on the total weight of the crude glycerol (CG).
Particular preference is given to crude glycerol (CG) having the following composition:

- 80 to 82% by weight of glycerol,
- 10 to 15% by weight of water,
- 5 to 7% by weight of inorganic salts comprising sodium chloride and
- 0.01 to 0.5% by weight of methanol,

where the percentages by weight are each based on the total weight of the crude glycerol (CG).
The inorganic salts are also referred to as ash. Ash constitutes the ignition residue of the crude glycerol (CG).
The crude glycerol (CG) may of course comprise further components which are obtained as impurities in the production of crude glycerol (CG). Preferably, the content of further components in the crude glycerol (CG), however, is below 1% by weight, more preferably below 0.5% by weight and especially below 0.1% by weight, based in each case on the total weight of the crude glycerol (CG).
Crude glycerol (CG) at 20° C. has a density of 1.23 to 1.27 g per cm³. The viscosity of crude glycerol (CG) at 20° C. is in the range from 700 mPa*s to 1200 mPa*s. The viscosity of the crude glycerol (CG) depends on the water content and any inorganic salts present in the crude glycerol (CG). The organic compounds present in crude glycerol (CG) are preferably methanol, especially in concentrations in the range from 0.01 to 0.5% by weight, based on the total weight of the crude glycerol (CG). The inorganic salts present are preferably sodium chloride and/or potassium chloride, especially in concentrations in the range from 5 to 7% by weight, based on the total weight of the crude glycerol (CG). Crude glycerol (CG) has the advantage that it is not of toxicological concern and is biodegraded. Crude glycerol (CG) can therefore also be used in ecologically sensitive areas as a constituent of a formulation for production of mineral oil.
In the last few years, the production of biodiesel, particularly in the European Union, has risen rapidly. The production of crude glycerol (CG) in the European Union has reached a volume of approximately 1 million tonnes. A viable use for the crude glycerol (CG) obtained in biodiesel production is a great economic problem which has not been solved to date. The invention enables a viable use of the wastes obtained in biodiesel production (crude glycerol (CG)). Crude glycerol (CG) additionally has the advantage of being available inexpensively and in large volumes.
Use of the Formulation (F) as a Composition for Mineral Oil Production
Particularly suitable formulations (F) are those which comprise at least 10% by weight of crude glycerol (CG), based on the total weight of the formulation (F). The invention thus also provides for the use of a formulation (F) comprising at least 10% by weight of crude glycerol (CG), based on the total weight of the formulation, as a composition for mineral oil production. In addition, the invention also provides for the use of an aqueous formulation (F) comprising at least 10% by weight of crude glycerol (CG), based on the total weight of the formulation (F), as a composition for mineral oil production.
Additionally particularly suitable are formulations (F) which, as well as crude glycerol (CG), comprise water. The invention thus also provides for the use of a formulation (F) comprising 10 to 99% by weight of crude glycerol (CG), 1 to 90% by weight of water and 0 to 20% by weight of at least one inorganic salt, where the percentages by weight are each based on the total weight of the formulation (F), as a composition for mineral oil production.
Preferred inorganic salts are sodium chloride and/or calcium chloride, particular preference being given to calcium chloride.
The viscosity, density, freezing temperature and final viscosity of the formulations (F) can be matched to the geological conditions in the mineral oil deposit. If, for example, the deposit water (also called formation water) has a density (D_D), increasing the concentration of the crude glycerol (CG) present in the formulation (F) can increase the density (D_F) of the formulation (F) such that D_D<D_F. This achieves effective displacement of the deposit water and ultimately of the mineral oil. To further increase the density (D_F) of the formulation (F), inorganic salts, preferably sodium chloride and/or calcium chloride, can be added thereto.
If the mineral oil deposit is within cold regions of the earth and has a deposit temperature (T_D) and the outside temperature above ground is (T_OT), the freezing temperature (T_FF) of the formulation (F) can be reduced by the increase in the concentration of crude glycerol (CG) such that (T_D) is greater than or equal to (T_FF). It is also possible to reduce the freezing temperature (T_FF) such that (T_OT) is greater than or equal to (T_FF). This enables the use of the formulation also in regions where prevalent temperatures above ground are below freezing point, for example in the range from minus 50 to 0° C. This enables the use of the formulation (F) also in permafrost regions.
Freezing temperature is understood to mean the temperature at which the formulation (F) solidifies, i.e. forms a solid.
If the formulation (F) is used as a flooding composition for displacement of mineral oil from the mineral oil deposit, the viscosity, the density and the final viscosity of the formulations (F) can be matched to the viscosity and density of the mineral oil in order to optimize the displacement thereof.
The formulation (F) may further comprise further additives, for example surfactants, urea or water-soluble thickening polymers, such as cellulose ethers, glucosylglucans, xanthans or diutans, and synthetic polymers, such as polyacrylamide, or copolymers of acrylamide with monomers containing sulfo groups.
However, the formulation (F) preferably comprises not more than 1% by weight, more preferably not more than 0.5% by weight and especially not more than 0.1% by weight of further additives, based in each case on the total weight of the formulation (F).
The percentages by weight of the individual components of the formulation (F) are generally selected such that the sum thereof adds up to 100% by weight. Preference is given to formulations (F) which consist of the above-described components, i.e. crude glycerol (CG), optionally water, optionally inorganic salts.
The percentages by weight of water and optionally of sodium chloride and/or calcium chloride in the formulation (F) do not include the amount of the water and any amounts of sodium chloride and/or calcium chloride already present in the crude glycerol (CG). The percentages by weight of water and sodium chloride and/or calcium chloride in the formulation (F) should be understood as additional amounts of water and sodium chloride and/or calcium chloride. To calculate the total amount of the amount of water present in the formulation (F), the amount of water present in the crude glycerol (CG) and the amount of water additionally added should thus be added up. To calculate the total amount of sodium chloride and/or calcium chloride in the formulation (F), the amounts of sodium chloride and/or calcium chloride present in the crude glycerol (CG) and the amounts of sodium chloride and/or calcium chloride additionally added should likewise be added up.
In addition, particularly suitable formulations (F) are those which comprise at least 80% by weight, preferably at least 90% by weight and more preferably at least 99% by weight of crude glycerol (CG). The invention thus also provides for the use of a formulation (F) which comprises at least 80% by weight, preferably at least 90% by weight and more preferably at least 99% by weight of crude glycerol (CG), where the percentages by weight are each based on the total weight of the formulation (F), as a composition for mineral oil production.
In addition, particularly suitable formulations (F) are those which consist essentially of crude glycerol (CG). This is understood in the present context to mean formulations (F) comprising not more than 0.5% by weight and especially not more than 0.1% by weight of further components other than crude glycerol (CG).
Formulations (F) having concentrations of crude glycerol (CG) of at least 80% by weight have a growth-inhibiting effect on the microbiological fauna in the mineral oil deposit. It has been found that the growth of microorganisms is accelerated at concentrations of crude glycerol (CG) in the range from 1 to 25% by weight, preferably in the range from 10 to 25% by weight, of crude glycerol (CG). The present invention thus also provides for the use of a formulation (F) comprising 10 to 25% by weight of crude glycerol (CG), based on the total weight of the formulation (F), as a composition for mineral oil production, especially for acceleration of the growth of microorganisms.
Oil production processes using microorganisms have been described in the prior art as MEOR (microbial enhanced oil recovery) processes. In the case of the inventive use, the microorganisms can be added to the formulation (F).
It has been found that the inventive formulation (F) can be used as a flooding composition for tertiary mineral oil production. The present invention thus also provides for the use of a formulation (F) as a flooding composition for tertiary mineral oil production.
In the case of use of the formulation (F) as a flooding composition for tertiary mineral oil production, preference is given to formulations (F) which comprise, as well as at least 10% by weight of crude glycerol (CG), additionally water and optionally sodium chloride and/or calcium chloride and optionally additional additives, where the above remarks apply correspondingly to the concentrations.
In addition, it has been found that the inventive formulation (F) can be used as a formulation for blocking high-permeability zones in a mineral oil deposit. The present invention thus also provides for the use of a formulation (F) as a composition for blocking high-permeability zones in a mineral oil deposit. In the case of use of the formulation (F) as a composition for blocking high-permeability zones in a mineral oil deposit, preference is given to formulations (F) having concentrations of crude glycerol (CG) of at least 80% by weight.
The inventive formulation (F) is advantageously used in mineral oil deposits having temperatures in the range from 0 to 180° C. Particular preference is given to the use of the formulation (F) in mineral oil deposits having a deposit temperature (T_D) below 60° C. Especially preferred is the use of the formulation (F) in mineral oil deposits having a deposit temperature (T_D) in the range from 0 to 40° C., more preferably in the range from 2 to 30° C. The present invention thus also provides for the use of the formulation (F) in a mineral oil deposit having a deposit temperature below 60° C., preferably in the range from 0 to 40° C., more preferably in the range from 2 to 30° C., as a composition for mineral oil production from mineral oil deposits.
The use of the formulation (F) enables balancing of the profile of the flood front (also referred to as profile modification). The present invention thus also provides for the use of the formulation (F) as a composition for balancing the profile of the flood front in a mineral oil deposit.
The inventive formulation (F) does not form a gel when the temperature is altered. When the temperature rises, the viscosity of the formulation (F) is lowered; when the temperature is reduced, the viscosity of the formulation (F) rises.
The inventive formulations (F) can be produced by simple processes, for example by simple mixing of the liquid components, and optionally by dissolution of solid components in the liquid components.
If the formulation (F) comprises water, it is possible to use fully demineralized water, tapwater, seawater, partially demineralized seawater or water which has been produced from the mineral oil deposit (called deposit or formation water). If the formulation (F) comprises inorganic salts, preference is given to using seawater or formation water.
The viscosity of the undiluted crude glycerol (CG) at a temperature of 20° C. is in the range from 700 to 1200 mPa*s and is much higher than the viscosity of the flood water which is used in conventional flooding. The viscosity of the formulation (F) depends particularly on the concentration of crude glycerol (CG) and water. The higher the crude glycerol (CG) concentration, the higher the viscosity of the formulation (F). Conversely, the viscosity of the formulation (F) decreases with increasing water concentration, i.e the higher the water concentration of the formulation (F), the lower the viscosity of the formulation (F). By varying the aforementioned concentrations, it is thus possible to adjust the viscosity of the formulation (F).
A further advantage of the inventive formulation (F) is that the viscosity of the formulation (F) increases with falling temperature. The viscosity of the formulation (F) can be adjusted such that it is higher by a factor of 10 to 100 than the formation water present in the deposit. Formation water in the present context is also understood to mean the flooding water which may have been injected in a preceding step into the deposit, for example in the course of secondary production processes. As a result of the higher viscosity of the formulation (F), possibly in conjunction with an elevated density, the formation water, which has a much lower viscosity and density, is effectively displaced, as a result of which a profile modification of the flood front and mobilization of mineral oil in stagnation zones are achieved.
The formulation (F) can be injected into the mineral oil deposit in large volumetric masses, for example in amounts of 500 to 50 000 m³.
Since the viscosity of the formulation (F) decreases at high temperatures, it has been found to be advantageous to use the formulation (F) with a temperature (T_F) higher than the deposit temperature (T_D).
At the temperature (T_F), the viscosity of the formulation (F) is lower than at the temperature (T_D). As a result of this, the formulation (F) can penetrate deep into the mineral oil deposit and fills especially zones therein which have been washed out, i.e. zones with high permeability. In the mineral oil deposit, the formulation (F) cools down, as a result of which the viscosity of the formulation (F) rises and the mobility of the formulation (F) decreases significantly.
Crude glycerol (CG) dissolves readily in water, as a result of which the concentration of crude glycerol (CG) decreases relatively rapidly, especially at the edge and at the flood front. In the core region of the volumetric zone, the mobility of the formulation (F) is much lower, ideally virtually 0.
Process for Producing Mineral Oil from an Underground Mineral Oil Deposit:
The present invention also provides a process for tertiary production of mineral oil from underground mineral oil deposits having a deposit temperature T_D, into which at least one injection well and at least one production well have been sunk, comprising at least the following process steps:

- i) injecting a flooding composition through at least one injection well into the mineral oil deposit, using, as the flooding composition, a formulation (F) having a temperature T_Fhigher than the temperature T_D,
- ii) cooling the flooding composition from step i) in the mineral oil deposit and
- iii) injecting a further flooding composition through at least one injection well into the mineral oil deposit and withdrawing mineral oil through at least one production well.

The process according to the invention for producing mineral oil is a process for tertiary mineral oil production, i.e. it is employed after primary mineral oil production has stopped due to the autogenous pressure of the deposit and the pressure in the deposit has to be maintained by injection of water and/or steam (secondary production) or by injection of an aqueous polymer solution (tertiary production).
For the formulations (F) used in the process according to the invention, the remarks and preferences expressed above regarding the use of the formulation (F) apply correspondingly.
The use of the formulation (F) in a process for producing mineral oil from an underground mineral oil deposit allows watering-out of production to be reduced and the level of oil recovery from the mineral oil deposit to be enhanced.
The process according to the invention has the advantage that, even in deposits with low temperature, high-permeability zones can be blocked selectively by means of the formulation (F). The process enables blockage even of washed-out rock zones in the deposit which have been cooled (for example by water flooding). The distance between the borehole (the injection well) and the zone in which the mobility of the formulation (F) decreases due to the viscosity rise can be regulated in the process according to the invention particularly through the amount of crude glycerol (CG) and the temperature T_Fwith which the formulation (F) is injected into the mineral oil deposit. This achieves efficient blocking of high-permeability zones, reduces watering-out of production and increases the level of oil recovery.
In a preferred embodiment, the process according to the invention is employed in mineral oil deposits having a deposit temperature T_Dbelow 60° C., more preferably in the range from 0 to 40° C. and especially in the range from 2 to 30° C.
The deposits may be deposits for all kinds of oil, for example those for light or heavy oil. In one embodiment of the invention, the deposits are heavy oil deposits, i.e. deposits comprising mineral oil having an API gravity of less than 22.3° API.
The optimal area for the use of the formulation (F) is in what are called “mature” deposits comprising oils having moderate or low viscosity.
The viscosity of the formulation (F) used as the flooding composition depends predominantly on the concentration of the crude glycerol (CG) used and on the deposit temperature. It should be matched to the viscosity of the mineral oil present in the mineral oil deposit and can be determined more accurately with the aid of the ratio (A) between the flooding composition mobility (Mw) and the mineral oil mobility (Mo).
A=Mw/Mo=(krw/μw)/(krw/μo),
krw—relative permeability of the mineral oil deposit for the flooding composition,
kro—relative permeability of the mineral oil deposit for mineral oil,
μo—mineral oil viscosity,
μw—viscosity of the flooding composition.
μw relates here to the viscosity of the flooding composition under the conditions in the mineral oil deposit. Ideally, the viscosity of the flooding composition (under the conditions in the mineral oil deposit) is adjusted so as to result in A values of <1. At A<1, the person skilled in the art expects piston-like displacement of the oil. The optimal ratio (A) between the flooding composition mobility (Mw) and the mineral oil mobility (Mo) is unattainable in some cases particularly for high-viscosity oils, since unrealistically high injection pressures have to be developed. It is therefore also necessary to work with A values of >1. However, even a relatively small increase in the viscosity of the flooding composition tends to improve the mineral oil yield.
In the case of optimization of the properties of the flooding composition comprising crude glycerol (CG), the viscosity of the flooding composition (μw) entered into the formula A=Mw/Mo is the viscosity after cooling in the deposit (final viscosity). The permeability is measured in darcies. The viscosity is measured in mPa*s.
The process according to the invention can be employed as soon as production in secondary production processes experiences excessive watering-out, or what is called a water breakthrough is registered. This is generally the case when a mixture comprising more than 70% by weight, particularly more than 90% by weight, of deposit water is withdrawn from the production well, based on the total weight of the mixture withdrawn from the production well. In the event of a water breakthrough, water flows through high-permeability zones from the injection well to the production well. Highly permeable zones, however, need not necessarily be obtained as a result of the water flooding, but may also be present naturally in a formation. In addition, it is possible that permeable zones have already been created in a process step preceding the process according to the invention.
For preparation for the process according to the invention, it may be advantageous to measure the temperature in the region of the injection well and to determine the temperature range of the deposit in the region under the influence of flooding. Methods for determining the temperature range in a mineral oil deposit are known in principle to those skilled in the art. The temperature distribution is generally undertaken from temperature measurements at particular sites in the formation in combination with simulation calculations, and the simulation calculations take account of factors including amounts of heat introduced into the formation and the amounts of heat removed from the formation. Alternatively, each of the regions may also be characterized by the average temperature thereof. It is clear to the person skilled in the art that the analysis of the temperature range outlined constitutes merely an approximation of the actual conditions in the formation.
In the course of the process according to the invention, highly permeable zones of the mineral oil deposit in the region between the injection wells and the production wells are blocked by injecting the formulation (F) through the at least one injection well.
Process Step i)
According to the invention, at least one formulation (F) is used for this purpose. It is also possible to successively inject two or more formulations (F) of different composition.
According to the invention, the formulation (F) is injected into the mineral oil deposit through one or more injection wells. The injection of the formulation (F) may optionally be followed by further water flooding in order to displace the formulation (F) further into the mineral oil deposit. In the context of the present invention, further flooding refers to the water volume which is injected directly after the injection of the formulation (F) in order to bring the formulation (F) to the desired site in the mineral oil deposit underground. However, due to the low viscosity of the formulation (F), this is not absolutely necessary. In one embodiment, no further flooding follows process step i).
To execute the process, at least one production well and at least one injection well are sunk in the mineral oil deposits. In general, a deposit is provided with several injection wells and with several production wells.
The deposit temperature can be altered through the use of the process according to the invention, typically at least within the region between the injection wells and the production wells.
In process step i), one or more flooding compositions are injected through the at least one injection well into the mineral oil deposit.
Preferably, T_F, with which the formulation (F) is injected into the mineral oil deposit in process step i), is at least 5° C. above T_D, preferably at least 15° C., more preferably at least 20° C. and especially at least 25° C. above T_D. It is also possible to use the formulation (F) with higher temperatures T_D. The temperature T_F, however, is preferably below the boiling point of the formulation (F) under the pressure conditions in the mineral oil deposit. The final viscosity of the formulation (F) in the deposit depends on the concentration of the formulation (F) and on the deposit temperature. The final viscosity of the formulation (F) is understood to mean the viscosity of the formulation (F) under deposit conditions (possibly after cooling). The greater the difference between T_Fand T_D, the deeper the formulation (F) penetrates into the deposit (for a given T_D). The effect of temperature on the viscosity is shown in FIG. 3.
The temperature of the formulation (F) used depends on the deposit temperature T_D. In order to satisfy the above temperature conditions, it may be necessary to heat the formulation (F) prior to injection. This can be effected by means of suitable heating elements which may be arranged above ground or within the injection well. The heating of the formulation (F) lowers the viscosity of the formulation (F). The formulation (F) can penetrate far into the mineral oil deposit as a result and fill particularly zones of high permeability therein. After deep penetration in the deposit, the formulation (F) cools down and the viscosity of the formulation (F) rises. This also increases the efficiency of the profile modification and the level of oil recovery.
The aims of heating the formulation (F) prior to injection are as follows:

- deep injection of the formulation (F) into the deposit,
- injection of heat into the deposit,
- facilitation of the pumping of the formulation (F).

When the formulation (F) is used as a flooding composition, for example in the case of development of the deposits with relatively homogeneous permeability, the optimal concentration of the formulation (F) is defined according to formula (A), and the formulation (F) is injected into the deposit without preheating.
Process Step ii)
In process step ii), the formulation (F) used as a flooding composition is cooled in the mineral oil deposit. This is preferably effected as a result of the formulation (F) releasing heat to the surrounding rock formations, the formation water, and possibly the mineral oil.
In a preferred embodiment, the formulation (F) in process step ii) is cooled to such an extent that T_Fis not more than 10° C. above T_D. As described above, the viscosity of the formulation (F) increases as a result of the cooling, as a result of which the mobility of the formulation (F) decreases and highly permeable zones are blocked.
Prior to the performance of process step iii), a further composition for blocking of high-permeability zones can be injected into the mineral oil deposit. This further composition for blocking of high-permeability zones is different than the formulation (F) in process steps i) and ii). The injection of the further composition for blocking of high-permeability zones may precede or follow the cooling of the formulation (F).
Suitable further compositions for blocking of high-permeability zones are formulations (F1) which have a high viscosity under the conditions in the mineral oil deposit. The further composition for blocking of high-permeability zones preferably forms a gel bank in the mineral oil deposit.
The further composition for blocking of high-permeability zones thus delimits the formulation (F) injected in process step i). The injection of a further flooding composition in process step iii) thus prevents subsequent dilution of the formulation (F) for example by water flooding. This delimits the formulation (F) from the further flooding composition.
As a further composition for blocking of high-permeability zones, particular preference is given to formulations (F1) comprising 10 to 40% by weight of crude glycerol (CG), 0.1 to 40% by weight of cellulose ether and 2 to 40% by weight of urea, where the percentages by weight are each based on the total weight of the formulation (F1). Under the action of the deposit temperature, the formulations (F1) form gels having viscosity well above the viscosity of the crude glycerol (CG).
As a further composition for blocking of high-permeability zones in deposits having temperatures below 60° C., it is also possible to use known inorganic aqueous mixtures based on urea, aluminum hydrochloride and urotropin.
The formulation (F1) forms a gel under the conditions in the mineral oil deposit.
The ending of process step ii) and injection of the formulation (F1) may be followed by a wait for one to three days. This is advantageous in order to promote gel formation in formulation (F1).
Process Step iii)
In process step iii), one or more further flooding compositions are injected into the mineral oil deposit and the production of mineral oil through at least one production well is continued. The further flooding compositions used may, for example, be nitrogen, carbon dioxide, water, and water comprising the customary additives known to those skilled in the art, such as thickeners and surfactants, preferably water or water comprising additive.
The “further flooding composition” may be a conventional flooding composition which is used predominantly for displacement of the mineral oil (water flooding, polymer flooding, crude glycerol flooding). In order to enhance the yield, the mobility of the formulation (F) which is used in step i) should be less under deposit conditions (final mobility) than the mobility of the mineral oil, and less than the mobility of the further flooding composition which is used in step iii). The mobility of the further flooding composition in step iii) should be less than or equal to the mobility of the mineral oil in the deposit. This enables efficient displacement of the mineral oil and minimal disruption of the deposit zones filled with formulation (F) from i). The mobility of the formulation (F) from i) is controlled by the crude glycerol concentration and the salt content, and the mobility of the formulation (F) from iii) is controlled, for example, by the concentration of the corresponding thickener. The dependence of the viscosity (mobility) on crude glycerol concentration studied is shown in FIG. 3.
The present invention thus also provides a process wherein the mobility of the formulation (F) used in process step i) under deposit conditions (final mobility) is less than the mobility of the mineral oil and less than the mobility of the further flooding composition from process step iii), the mobility of the further flooding composition from process step iii) being less than or equal to the mobility of the mineral oil.
The term “mineral oil” in this context does not of course mean single-phase oil, but means the customary emulsions which comprise oil and formation water and are produced from mineral oil deposits.
The injection of the further flooding composition results in formation, in the region between the injection well and production well, of a zone in which the mineral oil is displaced.
The oil production in process step iii) can be performed by customary methods, for example by injection of one or more further flooding compositions through at least one injection well into the mineral oil deposit, and mineral oil is withdrawn from the at least one production well.
As a further flooding composition, preference is given to using a formulation (F) having a lower crude glycerol concentration (CG) than the formulation (F) used in step i). The present invention therefore also provides a process in which the further flooding composition used in step iii) is a formulation (F) having a lower crude glycerol concentration (CG) than the formulation (F) used in step i).
The formulation (F) used in step iii) preferably comprises at least 10% by weight less crude glycerol (CG) than the formulation (F) used in step i).
The at least one injection well through which the further flooding composition is injected in process step iii) may be the injection well already used for injection of the formulation (F) in step i). It is also possible to inject the further flooding composition in process step iii) through another suitable injection well.
The mineral oil production can of course also be continued by means of other methods known to those skilled in the art. For example, the further flooding composition used may also be aqueous solutions of silicate-containing substances or thickening polymers (tertiary production). These may be synthetic polymers, for example polyacrylamide or acrylamide-comprising polymers. In addition, it is also possible to use biopolymers, for example polysaccharides.
It is also possible, after process step iii), to perform process steps i), ii) and iii) once again. This can be effected at regular intervals, for example once per year. In general, the process according to the invention is repeated when a water breakthrough is registered in mineral oil production in process step iii) from the production well. More particularly, the process is repeated when critical watering-out of production is attained in mineral oil production in process step iii). This is the case typically when watering-out of production is above 70 to 90% by weight. This means that a mixture comprising 70 to 90% by weight of deposit water, based on the total weight of the mixture withdrawn from the production well, is withdrawn from the production well.
Advantages
The process according to the invention for mineral oil production has the advantages which follow. The components present in formulation (F) are biodegradable and ecologically very substantially safe. The process according to the invention for production of mineral oil enables effective displacement of the mineral oil and modification of the flooding profile through the possible blockage of permeable regions and channels in the mineral oil deposit, as a result of which rapid water breakthrough is prevented. This is also possible at a relatively large distance from the injection well. The process according to the invention is additionally inexpensive, especially through the use of crude glycerol (CG), and allows efficient profile modification even in mineral oil deposits with relatively low temperatures.

The invention is illustrated in detail by the working examples and figures which follow.

FIG. 1: Dependence of the density of a formulation (F) comprising water and glycerol on the glycerol concentration

FIG. 2: Dependence of the boiling temperature of a formulation (F) comprising water and glycerol on the glycerol concentration

FIG. 3: Dependence of the viscosity of a formulation (F) comprising water and glycerol on the glycerol concentration

FIG. 4: Scheme of a mineral oil deposit section prior to commencement of the process according to the invention

FIG. 5: Scheme of a mineral oil deposit section after performance of process step i)

FIG. 6: Scheme of a mineral oil deposit section after cooling of the formulation (F) (process step ii))

FIG. 7: Scheme of a mineral oil deposit section after injection of the further composition for blocking of high-permeability zones (formulations (F1))

In FIGS. 4 to 7, the reference numerals are defined as follows:
1 Injection well
2, 3, 4 Production wells
5 Zone of high permeability (washed-out zone)
6 Near zone filled with formulation (F) prior to cooling
7 Zone filled with formulation (F) after cooling
8 Gel bank
FIG. 1 shows the dependence of the density (at 20° C.) of the formulation (F) comprising glycerol and water on the glycerol content. Plotted on the ordinate (Y axis) is the density (D) in g/cm³. Plotted on the abscissa (X axis) is the glycerol concentration (C_Gly) in % by weight.
FIG. 2 shows the dependence of the boiling temperature of the formulation (F) comprising glycerol and water on the glycerol content at standard pressure. Plotted on the ordinate (Y axis) is the boiling temperature (T_S) in ° C. Plotted on the abscissa (X axis) is the glycerol concentration (C_Gly) in % by weight.
FIG. 3 shows the dependence of the viscosity (at different temperatures) of the formulation (F) comprising glycerol and water on the glycerol content. Plotted on the ordinate (Y axis) is the viscosity (Visc) in mPa*s. Plotted on the abscissa (X axis) is the glycerol concentration (C_Gly) in % by weight.
FIG. 4 shows a mineral oil deposit, after flooding for several years, which has an inhomogeneous permeability. The region 5 represents a zone of high permeability between the injection well 1 and the production well 4. Hydrodynamic communication between wells 1 and 4 is very good. Outside zone 5, there are regions comprising mineral oil (called stagnant oil) in the deposit. In zone 5, a deposit temperature of 20° C. is predicted. A formulation (F) comprising 85% by weight of crude glycerol (CG) and 15% by weight of water is injected through injection well 1.
The temperature (T_F) of the formulation (F) corresponds at first to the environment/storage temperature above ground and is 15° C. At this temperature, the formulation (F) has a viscosity of 100 mPa*s. The mineral oil viscosity (under deposit conditions) is 40 mPa*s.
In order to reduce the viscosity of the formulation (F) in a controlled manner prior to injection into the mineral oil deposit, the formulation (F) is heated above ground to 40° C. This reduces the viscosity of the formulation (F) to 10 mPa*s. Subsequently, the formulation (F) is injected through injection well 1. The low-viscosity formulation (F) follows the flood paths that the flooding water took previously in the course of secondary production. This fills the near zone 6 of the injection well 1 with the formulation (F) (FIG. 5).
The low viscosity of the formulation (F) allows it to penetrate relatively deep into zone 5. After cooling of the formulation (F) in the deposit under the action of the low deposit temperature (T_D), the viscosity of the formulation (F) in the near zone 6 rises to 70 to 80 mPa*s, and the zone 7 forms (see FIG. 6). The formulation (F) forms a high hydraulic resistance in zone 7.
Subsequently, process step iii) is performed and a further flooding composition (for example water) is injected through the injection well (see FIG. 6). Due to the high hydraulic resistance in zone 7, the further flooding composition takes other paths (symbolized by the curved arrows). As a result, mineral oil outside the high-permeability zone 5 is displaced and can be withdrawn through production wells 2 and 3.
FIG. 8 shows a further embodiment. In this case, before or after cooling of the formulation (F) and formation of zone 7, a further flooding composition (for example water) is not injected directly. Instead, a further composition is first injected to block high-permeability regions. Since the temperature of the deposits is low, preference is given to using the formulation based on urea, aluminum hydrochloride and urotropin.
This formation gelates in the near region of the injection well. A relatively small portion of this formulation is injected through the injection well. The formulation forms a high-viscosity gel bank 8 in the mineral oil deposit between zone 7 and the injection well. This protects zone 7 from dilution by the further flooding composition (for example water) used subsequently. This minimizes the dynamic properties/movement of zone 7 and the dilution of the crude glycerol (CG) in zone 7.
Subsequently, a further flooding composition is injected through injection well 1, for example water or thickened water. It is optimal when the viscosity of the further flooding composition (post-flooding composition) is much less than the final viscosity of the crude glycerol (CG) in zone 7 and is equal to or somewhat higher than the mineral oil viscosity. As a result, mineral oil present outside the highly permeable zone 5 is displaced and can be withdrawn through production wells 2 and 3.
It is also possible to inject formulation (F1) into the mineral oil deposit prior to the cooling of the formulation (F).
This example describes an execution variant of the process in the development of a “mature” deposit with marked inhomogeneity of the permeability. The main purpose of injecting the formulation (F) (step i)) into the deposit is the modification of the flood profile.
Another important field of use of the process is the use of the formulation (F) predominantly for the displacement of the mineral oil. In this case, the deposit is flooded with the formulation (F) (the process is then limited to step i)). For this purpose, conventional technologies are used.

Claims

1.-12. (canceled)

13. A process for tertiary production of mineral oil from underground mineral oil deposits having a deposit temperature T_D, into which at least one injection well and at least one production well have been sunk, comprising at least the following process steps:

i) injecting a flooding composition through at least one injection well into the mineral oil deposit, using, as the flooding composition, a formulation (F) having a temperature T_Fhigher than the temperature T_D,

ii) cooling the flooding composition from step i) in the mineral oil deposit and

iii) injecting a further flooding composition through at least one injection well into the mineral oil deposit and withdrawing mineral oil through at least one production well, wherein the formulation (F) comprises crude glycerol (CG) having the following composition:

80 to 90% by weight of glycerol,

10 to 20% by weight of water,

0 to 10% by weight of inorganic salts and

0 to 1% by weight of organic compounds,

where the percentages by weight are each based on the total weight of the crude glycerol (CG).

14. The process according to claim 13, wherein the formulation (F) comprises at least 10% by weight of crude glycerol (CG), based on the total weight of the formulation (F).

15. The process according to claim 13, wherein the formulation (F) comprises 10 to 99% by weight of crude glycerol (CG), 1 to 90% by weight of water and 0 to 20% by weight of at least one inorganic salt, where the percentages by weight are each based on the total weight of the formulation (F).

16. The process according to claim 13, wherein the formulation (F) comprises at least 80% by weight of crude glycerol (CG), where the percentages by weight are each based on the total weight of the formulation (F).

17. The process according to claim 13, wherein the formulation (F) comprises at least 90% by weight of crude glycerol (CG), where the percentage by weight is based on the total weight of the formulation (F).

18. The process according to claim 13, wherein the formulation (F) comprises at least 99% by weight of crude glycerol (CG), where the percentage by weight is based on the total weight of the formulation (F).

19. The process according to claim 13, wherein the mobility of the formulation (F) used in process step i) under deposit conditions (final mobility) is less than the mobility of the mineral oil and less than the mobility of the further flooding composition from process step iii), the mobility of the further flooding composition from process step iii) being less than or equal to the mobility of the mineral oil.

20. The process according to claim 13, wherein the deposit temperature TD is below 60° C.

21. The process according of claim 13, wherein the flooding composition in step ii) is cooled to a temperature not more than 10° C. above the deposit temperature TD.

22. The process according claim 13, wherein the deposit temperature TD is in the range from 0 to 40° C.

23. The process according of claim 13, wherein the formulation (F) used as the flooding composition in step i) is heated to establish the temperature TF prior to injection into the mineral oil deposit.

24. The process according of claim 13, wherein step i) or step ii) is followed by injection of a further composition into the mineral oil deposit for blocking of highly permeable regions.

25. The process according of claim 13, wherein the further flooding composition used in step iii) is a formulation (F) having a lower crude glycerol concentration (CG) than the formulation (F) used in step i).

26. The process according to claim 24, wherein the further composition used for blocking of highly permeable zones is a formulation comprising 10 to 40% by weight of crude glycerol (CG), 0.1 to 40% by weight of cellulose ether and 2 to 40% by weight of urea, where the percentages by weight are each based on the total weight of the formulation.