WO2012107373A1

WO2012107373A1 - Multistage process for recovering petroleum using microorganisms

Info

Publication number: WO2012107373A1
Application number: PCT/EP2012/051912
Authority: WO
Inventors: Vladimir Stehle; Rajan Hollmann; Robert THUMMER
Original assignee: Wintershall Holding GmbH
Priority date: 2011-02-08
Filing date: 2012-02-06
Publication date: 2012-08-16
Also published as: EP2673333A1; CA2823750A1; EA201391044A1; EA023613B1

Abstract

Process for recovering petroleum from petroleum reservoirs by injection of aqueous flooding media into a petroleum formation through injection wells and extraction of petroleum through production wells, where the process comprises a plurality of cycles of process steps in which oil-mobilizing microorganisms and flooding water are alternately injected into the reservoir. Processes in which highly permeable regions of the petroleum formation are additionally blocked.

Description

Multi-stage process for the extraction of petroleum using microorganisms

The present invention relates to a method of extracting petroleum from oil reservoirs by injecting aqueous flooding media into a petroleum formation by injection drilling and withdrawal of petroleum through production wells, the method comprising several cycles of process steps alternately involving oil mobilizing microorganisms and flood water injected. It further relates to a process in which one additionally blocks highly permeable regions of the petroleum formation.

In natural oil deposits, petroleum is present in cavities of porous reservoirs which are closed to the earth's surface by impermeable facings. In addition to crude oil, including natural gas, a deposit will continue to contain more or less saline water. The cavities may be very fine cavities, capillaries, pores or the like, for example those having a diameter of only about 1 μΐη; however, the formation may also have areas of larger diameter pores and / or natural fractures.

After the hole has been drilled into the oil-bearing strata, the oil first flows to the production wells due to the natural deposit pressure and reaches the earth surface eruptively. This phase of crude oil production is called by the specialist primary production. With poor reservoir conditions, such as a high oil viscosity, rapidly decreasing reservoir pressure or large flow resistance in the oil-bearing layers, the eruption promotion comes to a halt quickly. With primary production, on average only 2 to 10% of the oil originally present in the deposit can be extracted. For higher-viscosity petroleum eruptive production is usually not possible.

In order to increase the yield, therefore, the so-called secondary production methods are used.

The most common method of secondary oil production is water flooding. In the process, water is injected into the oil-carrying layers through so-called injection bores. This artificially increases the reservoir pressure and forces the oil from the injection wells to the production wells. By flooding, the degree of exploitation can be significantly increased under certain conditions.

It is known to increase the oil yield by using suitable chemicals as auxiliaries for oil production. These measures are designed to increase the mobility of the oil in the formation so that it can be more easily pushed out of the formation as it floods. This phase of oil production is often referred to as "tertiary oil recovery" or "enhanced oil recovery" (EOR). For example, one can lower for this purpose the interfacial tension σ between the petroleum and the aqueous phase by the addition of suitable surfactants and thereby increase the mobility of the oil phase. This technique is also called A review of tertiary oil production techniques can be found, for example, in the Journal of Petroleum Science and Engineering 19 (1998) 265-280.

Another technique of tertiary mineral oil production is known to use microorganisms, in particular bacteria to increase the oil yield. This technique is known as "Microbial Enhanced Oil Recovery" (MEOR), which either injects suitable microorganisms, nutrients for the microorganisms and possibly oxygen into the petroleum formation, or promotes the growth of microorganisms already contained in the petroleum formation by injecting nutrients and possibly oxygen ,

There are several known mechanisms by which bacteria can increase the mobility of petroleum, such as by the formation of surfactants, reducing the viscosity of petroleum by degradation of high molecular weight hydrocarbons, formation of CO2, formation of organic acids, which can attack the rock formation and thus create new flow paths or by the separation of the petroleum from the rock surface. Processes for MEOR and microorganisms suitable for this purpose are disclosed, for example, in US Pat. Nos. 4,475,590, 4,905,761 or 6,758,270 B1.

RU 2 060 371 C1 discloses a method of conveying petroleum using microorganisms from a reservoir of inhomogeneous permeability, which has at least one injection and at least one production well. In the described method, the reservoir pressure is periodically increased and decreased. In phases of pressure increase, a nutrient solution is injected into the petroleum formation to activate microorganisms contained in the petroleum formation. Subsequently, the injection well is closed. By removing oil or water mixtures through the production bore, the pressure is reduced again.

RU 2 194 849 C1 discloses a method for conveying petroleum using microorganisms from a reservoir with inhomogeneous permeability, which has at least one injection and at least one production well. In the described method, the reservoir pressure is periodically increased and decreased. In phases of pressure increase, microorganisms and nutrient solution are respectively injected into the formation through the injection and production bores. In phases of pressure reduction, the injection well is closed and liquid is withdrawn through the production well of the formation. Preferably, mesophilic bacteria are injected into the injection well and thermophilic bacteria are introduced into the production well. A disadvantage of this method is the low efficiency, since the production well does not produce continuous oil, but is switched off regularly.

Ru 2 204 014 C1 discloses a method for pumping petroleum, in which a nutrient solution and carbon-oxidizing bacteria are injected into a petroleum formation and subsequently a biotechnologically produced polyacrylamide together with a crosslinker. When flooding but still more difficulties can occur. Ideally, a water front emanating from the injection well should press the oil evenly across the entire petroleum formation to the production well. In practice, however, a petroleum formation has regions with different high flow resistance. In addition to finely porous, oil-saturated reservoir rocks with a high flow resistance for water, there are also areas with low resistance to flow for water, such as natural or artificial fractures or very permeable areas in the reservoir rock. Such permeable areas may also be de-oiled areas. In the case of water flooding, the injected flood water naturally flows mainly through flow paths with low flow resistance from the injection well to the production well. As a result, the fine-pored, high-resistance, oil-saturated reservoir regions are no longer flooded, and increasingly more water and less oil are being pumped through the production well. In this context, the expert speaks of a "dilution of production." The above effects are particularly pronounced in heavy or viscous petroleum: the higher the petroleum viscosity, the more likely the rapid dilution of production.

In the prior art, therefore, measures are known to close such highly permeable zones between injection wells and production wells by means of suitable measures. This blocks highly permeable zones with low resistance to flow and forces the flood water back through the oil-saturated, low-permeability layers. Such measures are also known as "conformance control." An overview of measures for "conformance control" is given by Borling et al.

Oilfield Review (1994), pages 44 et seq. "Conformance Control" can be achieved by using comparatively low-viscosity formulations of certain chemical substances which can easily be pressed into the formation and their viscosity only after Pressing into the formation under the conditions prevailing in the formation conditions significantly increases. Such formulations contain inorganic or organic or polymeric components which are suitable for increasing the viscosity. On the one hand, the viscosity increase of the pressed-in formulation can easily be delayed. However, formulations are also known in which the increase in viscosity is essentially triggered by the increase in temperature when the injected formulation in the deposit gradually heats up to the reservoir temperature. Formulations whose viscosity increases only under formation conditions are known, for example, as "thermogels" or "delayed gelling system".

SU 1 654 554 A1 discloses mixtures of aluminum chloride or aluminum nitrate, urea and water, which are injected into the petroleum formation. At elevated temperatures in the formation, the urea hydrolyzes to carbon dioxide and ammonia. The release of the base ammonia significantly increases the pH of the water and precipitates a high viscosity aluminum hydroxide gel which clogs the highly permeable zones. US 4,889,563 discloses the use of aqueous solutions of aluminum hydroxide chloride in combination with urea or hexamethylenetetramine (urotropin) to block subterranean petroleum formations. Again, the hydrolysis of urea or hexamethylenetetramine in the formation leads to an increase in the pH and the precipitation of aluminum hydroxide.

US 4,844,168 discloses a method of blocking portions of high temperature petroleum formations comprising passing polyacrylamide and a polyvalent metal ion such as Fe (III), Al (III), Cr (III) or Zr (IV) into a petroleum formation having a reservoir temperature of at least 60 ° C pressed. Under the conditions in the formation, the amide groups -CONH2 partially hydrolyze to -COOH groups, the metal ions crosslinking the formed -COOH groups to form a gel with a certain time delay.

Further suitable mixtures for "conformance control" are disclosed, for example, by RU 2 066 743 C1, WO 2007/135617, US Pat. No. 7,273,101 B2, US Pat. No. 6,838,417 B2 or US 2008/0035344 A1.

Petroleum formations often do not have a homogeneous temperature distribution, but have more or less severe temperature gradients. Such temperature gradients can be of natural origin, but they can be caused in particular by measures of secondary and / or tertiary mineral oil production. During flooding, cold water is often injected into the formation for months or even years. As a result, the formation temperature in the area around the injection well generally decreases more or less strongly. As a typical example, Table 1 shows the temperature drop of the formation temperature for some deposits in northern Siberia after prolonged flooding:

Table 1: Site temperatures of various Siberian deposits S1 to S6 after prolonged flooding. The object of the invention was to provide an improved method for MEOR.

Accordingly, a process for extracting oil from subterranean oil reservoirs using microorganisms has been found, with at least one injection well and at least one production well drilled into the reservoir, reservoir temperatures (T ij ranging from 45 ° C to 120 ° C and from the reservoir oil promotes by injecting into the at least one injection well aqueous flood media and promotes oil through the at least one production well, and wherein the method comprises at least m cycles Zi to Z _m , wherein

• each of the process cycles Zi to Z _m the process steps

Mobilizing petroleum in the formation by injecting at least one aqueous formulation of oil mobilizing microorganisms, nutrients, and optionally an oxygen source, the microorganisms having an optimal growth temperature Tw, and

(II) injecting flood water having a temperature <45 ° C,

• the number of cycles m> 2,

• one per cycle Zi to Z _m, the process steps (I) and (II) in each case repeatedly alternately performs, and

• Tw of the injected microorganisms during the implementation of one of the cycles Zi is to Z _m not changed and give the _m microorganisms used a different optimum growth temperature T _w having at each of the process cycles Zi to Z, in the execution of the first process cycle Zi microorganisms are injected with the highest Tw, and each time the process cycle Z is carried out, microorganisms are injected which have a lower optimal growth temperature T _w than the microorganisms injected in the preceding process cycle Z. List of pictures:

Figure 1 Schematic representation of water flooding in the course of process step (II).

Figure 2 Schematic representation of the closure of the first flood zone

through gels.

Figure 3 Schematic representation of the formation of a new flood zone after closing the first flood zone.

More specifically, the following is to be accomplished for the invention:

The process of the present invention is applied after the primary oil production has ceased due to the inherent pressure of the reservoir and the pressure in the reservoir is maintained by injecting aqueous flooding media. It is particularly suitable for those deposits in which water flooding does not lead to a satisfactory result, because the oil yield is too low. This may be the case, for example, for deposits which are low permeable and / or the oil is not very mobile, so that it can not or only badly be pushed out by the flood water. However, the method is not limited to use in such deposits. deposits

The oil reservoirs may be deposits for all grades of oil, such as those for light or heavy oil, provided that the reservoir temperatures (T _L ) are in the range of 45 ° C to 120 ° C, preferably 50 ° C to 100 ° C, more preferably 50 ° C to 80 ° C. By reservoir temperature is meant the naturally prevailing temperature in the reservoir. It can be changed by the method steps described below.

method

To carry out the process at least one

Drilled production well and at least one injection well. As a rule, a deposit is provided with several injection wells and possibly multiple production wells. The injection wells allow aqueous flooding media to be injected into the oil reservoir, and production wells (also called production wells) are used to extract oil from the reservoir. The aqueous flooding media used in each of the individual process steps are described below. According to the invention are for Injecting the aqueous flooding media in the process steps described below always used the same injection wells; so it will not be drilled new injection wells. In the following, it will not be important whether the terms "injection well" or "production well" are used below in the singular or plural, but in each case "at least one injection well" or "at least one production well" should be meant.

The term "petroleum", of course, does not mean phase-pure petroleum, but rather the usual emulsions comprising oil and formation water, which are conveyed from crude oil reservoirs.The oil and water phases are separated from one another after conveying in a manner known in principle ,

Process Cycles Z The process according to the invention comprises m process cycles Zi to Z _m , where m> 2. In other words, the method comprises at least two process cycles Z.

Each of the process cycles Zi to Z _m comprises at least two process steps (I) and (II), which are each carried out alternately several times in succession. In step (I), suitable microorganisms are injected in formation capable of mobilizing petroleum in the formation. In process step (II) oil is pumped by water flooding.

According to the invention, the steps (I) and (II) are carried out alternately several times in succession, ie at least twice. Each of the cycles Zi to Z _m thus comprises at least the steps (I) - (II) - (I) - (II).

Process step (I)

In step (I), the crude oil formation is treated with suitable microorganisms for the mobilization of crude oil by injecting suitable microorganisms into the deposit. The microorganisms are in particular bacteria.

For the preparation of process step (I) expediently first geophysical and biochemical investigations of petroleum formation should be carried out. For the storage temperature and, where appropriate, the temperature distribution of petroleum formation is determined, at least in the area between the injection well and the production well. Methods for determining the temperature distribution of a crude oil deposit are known in principle to the person skilled in the art. It is usually carried out from temperature measurements at specific points of the formation in combination with simulation calculations, which is taken into account in the simulation calculations, inter alia, in the formation of introduced amounts of heat and the amount of heat dissipated from the formation. By means of biochemical A- The presence and amount of aerobic and anaerobic microorganisms in the borehole close to the injection well and the production well can be determined by means of analyzes. For this purpose, the formation samples are taken. In the course of process step (I) injected microorganisms can be both aerobic as well as anaerobic, preferably anaerobic microorganisms. Furthermore, nutrients and optionally an oxygen source, preferably an oxygen-containing gas, are injected into the petroleum formation. The components are formulated in a suitable manner in an aqueous medium for this purpose. The three components, microorganisms, nutrient solution and, optionally, an oxygen-containing gas can be injected together, or also successively in individual portions, so that microorganisms, nutrient solution and, optionally, the oxygen source mix together only in the formation. An oxygen-containing gas may be injected as such or it may preferably be an oxygen-containing flood medium, in particular oxygen-containing water or sols injected. The concentration of dissolved oxygen in the aqueous flooding medium, in particular water, may for example be 0.05 to 0.5 m ³ oxygen / m ³ flooding medium. The injection of an oxygen source, preferably an oxygen-containing gas, takes place when using aerobic microorganisms and is omitted when using anaerobic microorganisms. Suitable microorganisms for mobilizing petroleum in a petroleum formation are the

Expert in principle known, for example from the literature cited above. The mobilization of petroleum may be due to one or more of the following mechanisms: formation of surfactants, reduction of petroleum viscosity by degradation of high molecular weight hydrocarbons, formation of CO2 and / or methane, formation of organic acids capable of attacking the rock formation and thus new ones Creating flow paths or by the separation of the petroleum from the rock surface.

Examples of suitable microorganisms are described, for example, in "The Phylogenetic Diversity of Aerobic Organotropic Bacteria from the Dangang High-Temperature Oil Field".

T N. Nazina, D. Sh. Sokolova, N.M. Shestakova, A.A. Grigoryan, E. M. Mikhailova, T.L.Bambich, A.M. Lysenko, T.P. Tourova, A.B. Poltaraus, Qingxian Feng, Fangtian Ni, and S.S. Belyaev Microbiology, Vol. 3, 2005, pp. 343-351. Translated from Mikrobiologiya, Vol. 3, 2005, pp. 401-409 or "Use of Microorganisms in Biotechnology

for the Enhancement of Oil Recovery. S.S. Belyaev, I.A. Borzenkov, T.N.Nazina, E.P. Rozanova, I.F. Glumov, R.R. Ibatullin, and M.V. Ivanov, Microbiology, Vol. 5, 2004, pp. 590-598 ".

Examples of suitable microorganisms include anaerobic members of various genera such as Clostridium sp., Bacillus sp., Desulfovibrio sp., Arthrobacter sp., Mycobacterium sp., Micrococcus sp., Brevibacillus sp., Actinomyces sp. or Pseudomonas sp. Suitable nutrient solutions for microorganisms are known in principle to the person skilled in the art. They contain, for example, phosphate or ammonium salts. They may contain as main components, for example NaN0 ₃ , KN0 ₃ , NH ₄ N0 ₃ , Na ₂ HPO ₄ , NH ₄ Cl, trace elements such as B, Zn, Cu, Co, Mg, Mn, Fe, Mo, W, Ni, Se, vitamins such as Folic acid, ascorbic acid, riboflavin, electron acceptors such as S0 ₄ ^2_ , N0 ₃ ² , Fe ⁺³ , humic acids, mineral oxides, quinone compounds or combinations thereof.

The maximum growth rate of microorganisms depends on the temperature. The temperature at which the growth of microorganisms is greatest will be referred to as Tw. The person skilled in the art distinguishes between different classes of microorganisms, namely psychrophilic, mesophilic, thermophilic and hyperthermophilic bacteria, wherein the temperature ranges of maximum growth rate may be slightly differently defined depending on the literature citation. Table 3 below shows a common classification to be used for the present invention.

Minimum temperature optimum maximum temperature

Psychrophile - 5 ° C 12 to 15 ° C 25 ° C

Mesophiles 15 ° C 30 to 40 ° C 47 ° C

Thermophiles 40 ° C 55 to 75 ° C 90 ° C

Hyperthermophilic 70 ° C 80 to 90 ° C 1 10 ° C

Table 2: Minimum, maximum and optimal growth temperature for different classes of microorganisms.

Table 3 below shows some microorganisms, each having an optimum growth temperature:

Table 3: Optimum growth temperature of various microorganisms

Process step (II)

Subsequent to mobilizing petroleum in the formation by process step (I), petroleum is conveyed by injecting flood water into the injection well and extracting petroleum through the production well. The mobilized by the microorganisms oil is now so promoted by further water flooding. The flood water used may be any type of water, for example, fresh water, salt water or brine, and the water may optionally also contain other additives. The flood water used for injection has a temperature of less than 45 ° C, typically less than 25 ° C and, for example, less than 20 ° C. It may, for example, be seawater. The duration of the flood depends on the conditions in the formation; it can take months or even years.

Combination of Steps (I) and (II) According to the invention, steps (I) and (II) are carried out n times successively per cycle, where n> 2 and the number n can assume different values for each cycle. As a rule, n is a number from 2 to 5, preferably 2 or 3, The sequence of the process steps may therefore preferably be (I) - (II) - (I) - (II) or (I) - (II) - (I) - (II) - (I) - (II). Each cycle thus includes at least two M EOR process steps, each followed by water floods. The optimum growth temperature Tw of the microorganisms used during a cycle in the process steps (I) is not changed within one cycle, i. The same microorganisms are used during each cycle.

After the mobilization of petroleum in process step (I), the production is continued by injecting flood water (process step (II)).

In the course of process step (II), the floodwater pushes the mobilized petroleum in the direction of the production well, through which it can be removed. This forms a flow zone between the production and the injection well. This is shown schematically in Figure 1. Water is injected into the injection well (1) from there in the direction of the production well (2) and presses oil from the pores in the direction of the production well. The flow direction is indicated by the arrows (3). Within the (gray-shaded) zone (4) oil is at least partially displaced by the water front. The direction of the water front (3) as well as the size and location of the zone (4) are determined by the conditions in the deposit, for example the spatial dynamics of the permeability index, the fracture or local geological disturbances. The zone (4) may have a complicated branched shape, especially if there are multiple injection wells for water and multiple production wells on that section. In the flow zone (4), the flood water usually does not press the crude oil in front of it in a uniform manner. The reason for this is that even in the flow zone the permeability is generally not uniform. If more porous areas are present, for example fine gaps, fractures or cracks, the water preferably flows through these zones of lower flow resistance. In addition, the oil may be only partially removed from pores. For example, an oil droplet can remain in a pore, which is no longer carried along by the water flowing through this pore. With increasing duration of water flooding, More and more preferential flood paths for the water are forming. As a result, more and more water reaches the production well and accordingly increases the proportion of water in the extracted oil-water mixture with increasing duration of water flooding. The dilution of the production is therefore an indication that the aqueous flooding medium no longer flows evenly from the injection well to the production well through the formation, but has found preferential flooding paths through above-average permeable zones of the formation Flood water flowing through flood channels no longer mobilizes oil, or at least only insufficiently, and can still leave significant amounts of oil in the zone (4) that is flown through, and there is still some oil left in the crude oil formation outside zone (4).

Further petroleum is therefore recovered by re-performing process step (I) followed by re-performing process step (II). Combination of the process cycles Zi to Z _m

The method according to the invention comprises m process cycles Zi to Z _m . At least two of the process cycles are carried out, ie m> 2 applies. As a rule, m is a number from 2 to 5, preferably 2 or 3.

According to the invention, the microorganisms injected in each process cycle Zi to Z _{m have} a different optimal growth temperature Tw. Thus other microorganisms are used in each cycle Zi to Z _m, while the same microorganisms are used during each cycle, respectively.

In this case, in the execution of the first cycle Zi microorganisms having the highest optimal growth temperature Tw are injected. Each time a process cycle is repeated, microorganisms are injected which have a lower optimal growth temperature T _w than the microorganisms injected in the previously performed process cycle.

The optimum growth temperature Tw of the first injected portion of microorganisms is expediently dimensioned such that it corresponds approximately to the natural reservoir temperature TL, which lies between 45 ° C. and 120 ° C. When Tw and TL are about the same, the microorganisms in the formation grow fastest and thus oil in the formation is also well mobilized. In the execution of a first cycle Zi, in particular thermophilic and / or hyperthermophilic microorganisms can be used, depending on the TL.

At a preferred storage temperature TL in the range of 50 ° C to 80 ° C is usually started with thermophilic bacteria, such as a strain selected from the group of Streptococcus thermophilus, Geobacillus stearothermophilus, Thermus aquaticus, Streptomyces thermogriseus, Clostridium stercorarium, Thermovorax subterraneus or Geothermobacter ehrlichii.

In the above-described alternate embodiment of process steps (I) and (II), it should be noted that the flood water used for injection is comparatively cold and has a temperature of less than 45 ° C, as a rule, less than 25, as shown above ° C and, for example, less than 20 ° C. As a result of the injection of flood water, the temperature distribution in the crude oil formation changes with increasing duration of the flooding. As a result of the continued injection of cold flood water, first the temperature of the deposit at the location of the injection well decreases from the originally prevailing reservoir temperature TL. By flowing the flood water in the direction of the production well (ie the zone (4)), other areas of the flow-through zone can cool down. Naturally, the cooling effect at the injection well is strongest and decreases with increasing distance from the production well. In the flow-through zone (4) between the injection well (1) and the production well (2) thus forms a temperature gradient, the temperature tends to increase in the direction of the production well, but wherein the temperature within the flow-through zone-depending on the flow conditions- does not necessarily have to rise uniformly. The average temperature within the flood zone (hereinafter called TF) is thus less than the reservoir temperature TL. At an original reservoir temperature of 50 to 90 ° C, the temperature of the flooded zone may well drop to 25 to 45 ° C over time.

In the case of the described sequence of process steps (I) and (II) within one cycle, the same microorganisms are used, as described above, ie T _{w of} the microorganisms is unchanged, where Tw is adapted as well as possible to the temperature of the deposit during the first cycle Zi should be to achieve a rapid growth of microorganisms and thus a good mobilization of petroleum. With decreasing temperature TF within the cladding zone, the optimum growth temperature Tw of the microorganisms used during the first cycle is increasingly undershot. Accordingly, the growth of microorganisms is slowing down more and more and finally comes to an extreme halt in the extreme case. It is then no longer possible to mobilize oil.

According to the invention, therefore, for the repetition of the first cycle Zi, ie for the cycle Z2, microorganisms having a lower optimum growth temperature Tw than in the first cycle are used in order to take account of this cooling of the petroleum formation in the flooded region. T _w should therefore be chosen to be about TF. For the first repetition of cycle Z, for example, mesophilic microorganisms can be injected. If one has started at a storage temperature TL in the range of 50 to 80 ° C as described above, one can select the method after lowering the temperature to 30 ° C to 40 ° C, for example, with mesophilic bacteria selected from the group of Escherichia coli, Streptomyces coelicolor, Bacillus subtilis, Corynebacterium glutamicum, Pseudomonas putida, Salmonella enterica or Micrococcus luteus.

After further dropping of the temperature TF due to continued injection of water, a new cycle Z _{3 can be} started again, in which microorganisms are used with a further reduced Tw. In the repetition of the cycle Z, for example, psychrophilic microorganisms can be used.

If one has started at a storage temperature TL in the range from 50 to 80 ° C. as described above, then the method can be selected after the temperature has dropped below 25 ° C., for example using psychrophilic bacteria from the group of Flavobacterium antarcticum, Photobacterium profundum , Shewanella benthica, Chlamydomonas nivalis, Flavobacterium frigidarium, Leptothrix mobilis or Bacillus marinus.

The cycles can, in principle, be executed repeatedly m times, reducing Tw every time compared to Twe's previous cycle. The process cycles Z are preferably carried out two or three times in succession, more preferably twice.

By executing the cycles Z times, the formation is treated in accordance with the decreasing temperature of the flood zone TF, respectively, with microorganisms adapted Tw and thus achieves a particularly good de-oiling.

Optional process step (III)

In a further embodiment, the method optionally comprises an additional process step (III).

In process step (III), highly permeable regions of the formation can be blocked. The highly permeable regions are essentially the zone through which flows through in the region between the at least one injection bore and the at least one production bore, that is to say the zone which has only formed by carrying out the process cycles Z.

Techniques for blocking highly permeable regions of petroleum formations are known in principle to those skilled in the art, for example from the literature cited above. Here, suitable aqueous formulations are injected through the injection well into the formation, which can cause the highly permeable regions to become closed. The blocking of highly permeable regions of the formation is preferably carried out by injecting at least one aqueous, gel-forming formulation (F) through the injection well, the formulations forming highly viscous gels after being pressed into the deposit under the influence of the reservoir temperature. After being injected into the formation, the formulations (F) naturally flow essentially through the highly permeable regions and close them after the gel has formed. This is shown schematically in Figure 2. A gel plug (5) seals the high permeability areas between the injection and production wells. The aqueous gel-forming formulations (F) comprise, in addition to water, one or more different water-soluble or water-dispersible chemical components which are responsible for gelation. It is preferably at least two different components. These may be both inorganic components and organic components, and of course also combinations of inorganic and organic components.

For example, these may be formulations based on water-soluble polymers, as disclosed, for example, in US Pat. No. 4,844,168, US Pat. No. 6,838,417 B2 or US Pat. No. 2008/0035344 A1, or formulations based essentially on inorganic components, such as, for example, SU 1 654 554 A1, US Pat. No. 4,889,563, RU 2 066 743 C1, WO 2007/135617, US Pat. No. 7,273,101 B2 or RU 2 339 803 C2. Suitable formulations are also commercially available.

The temperature starting from gelation (hereinafter referred to as TGei) and the time at which this happens (hereinafter called tGei) can be influenced, for example, by the nature and concentration of the components. They can be adjusted so that between 20 ° C and 120 ° C, preferably 30 to 120 ° C and more preferably 40 to 120 ° C gels are formed. The cited citations contain information. The formulations can thus be adjusted so that the formulations form gels at the desired location of the highly permeable areas and block the high-permeability areas.

In a preferred embodiment, formulation (F) is an acidic aqueous formulation, preferably having a pH <5, which comprises at least

• a metal compound dissolved in it, which can form gels when mixed with bases, as well as

A water-soluble activator comprising, at a temperature T> TG, an increase in the pH of the aqueous solution. In addition to water, the formulation may optionally include other water-miscible organic solvents. Examples of such solvents include alcohols. In general, however, the formulations (F) should comprise at least 80% by weight of water with respect to the sum of all solvents of the formulation, preferably at least 90% by weight and more preferably at least 95% by weight. Most preferably, only water should be present.

The dissolved metal compound is preferably aluminum compounds, in particular dissolved aluminum (III) salts, such as, for example, aluminum (III) chloride, aluminum (III) nitrate, aluminum (III) sulfate, aluminum (III) acetate or aluminum (III ) acetylacetonate. However, it may also be partially hydrolyzed aluminum (III) salts, such as, for example, aluminum (III) hydroxychloride. Of course, mixtures of several different aluminum compounds can be used. The pH of the formulation is generally <5, preferably <4.5. Preference is given to aluminum (III) chloride, aluminum (III) nitrate or aluminum (III) sulfate, very particularly preferably aluminum (III) chloride. Suitable water-soluble activators are all compounds which, on heating to a temperature T> TGei, release bases in an aqueous medium or bind acids and thus ensure an increase in the pH of the solution. By increasing the pH value, highly viscous, water-insoluble gels are formed, which comprise metal ions, hydroxide ions and optionally further components. In the case of the use of aluminum compounds, an aluminum hydroxide or oxide hydrate gel can form, in which, of course, further components, such as for example the anions of the aluminum salt used, may comprise. As water-soluble activators, for example, urea, substituted ureas such as Ν, Ν'-alkyl ureas, in particular Ν, Ν'-dimethylurea, Hexamethylentetra- min (urotropin) or cyanates can be used, in particular urea, substituted urea substances or hexamethylenetetramine urea, for example hydrolyzed in aqueous Medium to ammonia and CO2. Of course, mixtures of several different activators can be used. It is preferably urea and / or hexamethylenetetramine. The formulations may further comprise other components which can accelerate or retard gelation. Examples include other salts or naphthenic acids.

The concentrations of the metal compounds used are selected by the skilled person so that a gel forms with the desired viscosity. He will therefore use the activator in such a concentration that a sufficient amount of base can be formed to lower the pH so much that a gel can actually precipitate. Furthermore, it is also possible to determine the gel formation time tGei by way of the amounts or the proportions. The higher the concentration of the activator, the greater the rate of gelation at a given metal compound concentration. This connection can the

Expert use, to speed up or slow down the gelation time TGei targeted. The rate of gel formation, after exceeding TGei, is naturally also determined by the temperature prevailing in the formation. In the case of aluminum, an amount of from 0.2 to 3% by weight of aluminum (III) based on the aqueous formulation has been proven. The amount of activator should be at least such that 3 moles of base per mole of Al (III) are released.

In Table 4 below, the time until gel formation is exemplary for a mixture of 8 wt.% AlC (calculated as anhydrous product, corresponds to 1, 6 wt.% Al (III)), 25 wt.% Urea and 67 wt.%. Water shown.

Table 4: Time to gelation at different temperatures

In Table 5 below, the time to gelation for various mixtures of AlC (calculated as anhydrous product), urea and water at 100 ° C and 100 ° C is shown.

Table 5: Time to gelation ("-" no measurement)

It can be seen that as the amount of activator urea decreases, the time to form the gel for both the 8 wt.% AICI ₃ series and the 4 wt.% AICI ₃ series becomes increasingly longer as the amount of urea decreases. The gelation time can thus be changed in a targeted manner via the ratio aluminum salt / urea.

Gel-forming formulations, which are particularly suitable for low storage temperatures, can be obtained by replacing urea as an activator in whole or in part by urotropin (hexamethylenetetramine) as an activator. Urotropin also releases ammonia under reservoir conditions. Such gel-forming formulations also lead

Temperatures below 50 ° C for gelation. Typical aqueous formulations may comprise 4 to 16% by weight of urea, 2 to 8% by weight of urotropin and 2 to 4% by weight of aluminum chloride or nitrate (calculated as the anhydrous salt) and water or salt water. Such formulations are disclosed, for example, in RU 2 066 743 C1. Table 6 below presents some of the formulations disclosed in RU 2,066,743 C1, pages 5 to 7 and their gelation at different temperatures.

Table 6: Gelation as a function of temperature and time

The described preferred formulations based on dissolved metal compounds, in particular aluminum salts and activators have the advantage that inorganic gels are formed. The gels are stable up to temperatures of 300 ° C. Furthermore, if necessary, the inorganic gels can also be removed from the formation very easily by injecting acid into the formation and dissolving the gels.

Procedure after carrying out process step (I I I)

After the optional execution of process step (I II), the oil production is continued, for example by flooding.

Preferably, the oil production is carried out by repeatedly executing process cycles Z. This is shown schematically in Figure 3. It forms a new Flutzone (6), from which oil is now extracted.

It should be noted that in the renewed execution of the process cycles Z and the sequence of optimal growth temperatures Tw starts again from the beginning.

For the repetition, the process cycles Z to Z _m - are carried out, where m '> 2, preferably 2 to 5 and particularly preferably 2 or 3.

For the first time execution of a cycle Zr after process step (II I) one starts with the highest Tw and then reduces Tw step by step from cycle to cycle according to the falling temperature in the flood zone. As a rule, the new flood zone (6) initially has the storage temperature or at least approximately the storage temperature and T _w is set accordingly.

Of course, further variants of the method according to the invention are possible. For example, it is possible to carry out method step (III) a second time and again a series of method cycles Zr to Z _m ".

Claims

claims

A method for extracting oil from subterranean oil reservoirs using microorganisms, wherein at least one injection well and at least one production well have sunk into the reservoir, the reservoir temperatures (T _L ) are in the range of 45 ° C to 120 ° C, and one of the oil reservoir promotes by injecting into the at least one injection well aqueous flood media and promotes oil through the at least one production well, characterized in that the method comprises at least m cycles Zi to Z _m , wherein

• each of the process cycles Zi to Z _m the process steps

(I) mobilizing petroleum in the formation by injecting at least one aqueous formulation of oil mobilizing microorganisms, nutrients and optionally an oxygen source, the microorganisms having an optimal growth temperature Tw, and

(II) injecting flood water having a temperature <45 ° C,

• the number of cycles m> 2,

• one per cycle Zi to Z _m, the process steps (I) and (II) in each case several times

one after the other alternately, and

• Tw of the injected microorganisms during the execution of each of the cycles Zi to Z _{m is} not changed, and wherein

^■ the _m microorganisms used a different optimum growth temperature T _w having at each of the process cycles Zi to Z,

^■ when performing the first cycle Zi microorganisms are injected with the highest Tw, and

^■ each time the process cycle Z is carried out, microorganisms are injected which have a lower optimum growth temperature T _w than the microorganisms injected in the preceding process cycle Z.

A method according to claim 1, characterized in that the flood water has a temperature <25 ° C.

Method according to claim 1 or 2, characterized in that m = 2.

4. Process according to claim 3, characterized in that in the first process cycle Zi thermophilic or hyperthermophilic and in the second process cycle Z2 mesophilic microorganisms are used.

5. The method according to any one of claims 1 to 4, characterized in that it is the oxygen source is an oxygen-containing gas.

6. The method according to any one of claims 1 to 5, characterized in that after performing a first cycle Zi highly permeable regions of the petroleum formation by means of a further process step (II I) completely or partially blocked and subsequent to step (I II) the oil production continues by injecting at least one aqueous, gel-forming formulation (F) into the formation, wherein the formulations (F) contain water and one or more water-soluble or water-dispersible components which after being injected into the deposit under the Influence of the reservoir temperature to form highly viscous gels.

7. A method according to claim 6, characterized in that the aqueous gel-forming formulation (F) is an acidic aqueous formulation which comprises at least:

• Water,

• Aluminum (II) compounds dissolved in it, which can form gels when mixed with bases, as well as

A water-soluble activator which raises the pH of the aqueous solution above a temperature TGei selected from the group consisting of urea, substituted ureas, hexamethylenetetramine or cyanates. 8. Process according to claim 7, characterized in that the aluminum (III) compound is at least one selected from the group of aluminum (III) chloride, aluminum (II) nitrate, aluminum (III) sulfate, aluminum (III) acetate or aluminum (III) acetylacetonate. 9. The method according to any one of claims 6 to 8, characterized in that the oil production continues after step (I I I) by means of water flooding.

10. The method according to any one of claims 6 to 8, characterized in that following the oil transfer in step (III) or a process step (III) subsequent water flooding by renewed execution of m 'process cycles Zr to Z _m - continues m '> 2 is. A method according to claim 10, characterized in that m '= 2 and in the first cycle Zr thermophilic or hyperthermophilic and in the second cycle Z2' mesophilic microorganisms used.