JPH03212593A - Recovering method for oil using cationic and anionic polymer - Google Patents

Abstract

PURPOSE:To efficiently generate a water insoluble gel and reduce the permeability of a stratum of high permeability by bringing a water soluble anionic polymer into contact with the stratum to which a water soluble cationic polymer is adsorbed in advance, so as to adjust the permeability of an oil stratum. CONSTITUTION:A water soluble cationic polymer is injected into and adsorbed to a stratum in advance and then a water soluble anionic polymer is brought into contact with the stratum. The amount of water soluble gels generated at the reaction of both polymers with each other is increased and stabilized so that the permeability of an oil stratum is adjusted in such a manner that the effect of lowering the permeability of a stratum of high permeability is increased. Also the water soluble cationic polymer is injected into the stratum from a production well and then the water soluble anionic polymer is injected therein from an injection well. Gelation reaction is caused only in a portion of high permeability distant from near the production well by avoiding the use of the same well, so as to enhance the efficiency, the injection property and the productivity of adjustment of the oil stratum.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for effectively recovering petroleum from a geological formation, and more specifically, it relates to a method for effectively recovering petroleum from a geological formation. This article relates to a method for adjusting the permeability of an oil layer and recovering oil.

[Prior Art] When crude oil is produced from an underground oil reservoir, a large amount of water is entrained along with the crude oil from the production well. The produced crude oil must be separated from its accompanying water, and the economic cost of this separation is an issue. More importantly, since the total production of the well is limited by the equipment, the associated water keeps crude oil production low. Reducing the amount of water involved increases the rate of crude oil production and also reduces the cost of separation, making it extremely effective for crude oil production.

The entrainment of water from production wells is mainly due to groundwater outflow from the strata outside the oil reservoir (water coning), and water or aqueous solutions injected by water flooding or tertiary flooding methods that inject other aqueous solutions into the oil reservoir. Oil flows out through a high permeability layer (a layer through which water can easily pass) or through fractures (cracks in the stratum) that exist in an oil layer. In other words, most oil layers consist of layers with different permeability (permeability), and water flooding or tertiary flooding using other aqueous solutions involves injecting water or an aqueous solution into these layers. This method attempts to push out the crude oil present in each layer, but the crude oil is pushed out only in the high permeability area, and the injected water in this area is quickly discharged from the production well (called breakthrough).
Therefore, a large amount of water is involved when producing crude oil. Furthermore, it becomes easier for water to pass through the areas where the crude oil has been pushed out by the injection water, reducing the production rate of crude oil from the low permeability areas where a large amount of crude oil still remains. Therefore, if it is possible to selectively plug some kind of plug only in areas with high permeability of the formation to prevent water from flowing, it will be possible to recover even more oil from this oil well.

Therefore, various techniques (oil reservoir adjustment methods) have been proposed to reduce water production.

This oil layer adjustment method improves the distribution of permeability throughout the oil layer by filling areas with high permeability with polymers, etc. Known techniques include the aluminum citrate method, anionic-cationic polymer method, and The chrome gel method is known. These methods are mainly used for the treatment of oil layers with fractures (large cracks in the oil layer, etc.) and water cones, whereas the chrome shell method is mainly used for treating oil layers with fractures (large cracks in the oil layer, etc.) and water cones, whereas the aluminum citrate method and anionic-cationic heavy The difference is that the coalescence method targets oil reservoirs with a distribution of high and low permeability.

The aluminum citrate method is based on crosslinking anionic and nonionic polymers with citric acid as a crosslinking agent. After preparing the base, ■ injecting an aqueous solution of aluminum citrate as a crosslinking agent and adsorbing it to the surface of the polymer, and then injecting an aqueous solution of a polymer that is easy to crosslink and reacting with the previously injected crosslinking agent. and, as a result, the polymer improves the permeability of the high permeability layer.

The anionic-cationic polymer method adjusts the permeability of the oil layer by reacting anionic and cationic polymers in the oil layer to form a water-insoluble gel.

There are two types of this method, and the representative methods are U.S. Pat. No. 3,779,316 (dispersion method) and U.S. Pat.
No. 17132 (sequential injection method). In the former case, ■ a dispersion of anionic polymer W10 emulsion in a cationic solution is injected into the oil layer, and ■ the dispersion injected into the high permeability layer is
The emulsion is then broken by a surfactant, causing the cationic and anionic polymers to react and form a water-insoluble gel.

The latter is a sequential polymer injection method in which an anionic polymer is injected into an oil layer and adsorbed, and then a cationic polymer is injected to form a water-insoluble gel to adjust the oil layer.

[Problems to be Solved by the Invention] Problems with these oil layer adjustment methods for oil layers without fractures include the following.

In the aluminum citrate method, the crosslinking of the polymer, that is, the coordination between aluminum and the polymer, is greatly affected by pH, and usually crosslinking does not proceed at a pH of about 7 or higher.

On the other hand, oil layers where the pH of the formation water is 7 or more are very common and distributed over a wide range, but a major drawback of this aluminum citrate method is that it cannot be applied to such oil layers.

The first problem with the dispersion method, which is one of the anionic-cationic polymer methods, is the stability of the dispersion.

In other words, since the anionic polymer dispersion contains cations and anions in an emulsion state, they tend to react with each other to form insoluble substances, and the formation of an insoluble gel progresses, especially due to mechanical shear during injection. Easy to do. On the other hand, when injecting a surfactant into the injected emulsion mixture later and inverting it to advance the gelation reaction and adjust the oil layer, it is very difficult to effectively advance the inversion in the stratum.
This is a major problem with illegality.

On the other hand, in the sequential injection method, which is another method of the anionic-cationic polymer method, a water-soluble anionic polymer is first injected, but this anionic polymer is not sufficiently adsorbed and retained on the surface of the deposited layer. The disadvantage is that even if the cationic polymer is injected later, the amount of insoluble gel produced is small and sufficient effects cannot be obtained.

The conventional techniques have the above-mentioned problems, and even if they are actually implemented, they are not very effective, and there is a particular need for a method for essential improvement.

[Means for Solving the Problems] The present inventors continued to study various methods for improving oil layers that do not have the above-mentioned drawbacks, and as a result, the present inventors added a water-soluble anionic polymer to a geological layer that had previously adsorbed a water-soluble cationic polymer. It was discovered that by bringing the polymer into contact and adjusting the permeability of the oil layer, a great effect that could not be obtained with conventional methods could be obtained, and the present invention was completed.

That is, if the cationic polymer is injected first, the amount of adsorption to the formation will be larger and it will be less likely to be washed away than if the anionic polymer is injected first.

This is because the composition of the rock in the formation is mostly sandstone, and its surface is negatively charged, so adsorption by ionic bonds of cationic polymers is much greater than that of anions.

As a result, the amount of water-insoluble gel produced when it reacts with the water-soluble anionic polymer to be injected later is large and stable, so the permeability reduction effect of the high permeability layer is very large.

In addition, this method involves sequentially injecting a water-soluble cationic polymer and a water-soluble anionic polymer into the oil layer and creating a water-insoluble gel through an ionic bonding reaction. There are no drawbacks such as difficulty in controlling the gelation reaction.

Furthermore, the present inventors did not inject the above-mentioned water-soluble cationic polymer and water-soluble anionic polymer from the same well, but first injected the water-soluble cationic polymer from a production well and adsorbed it to the high permeability layer of the oil layer. It has been found that even more remarkable effects can be obtained by injecting a water-soluble anionic polymer through an injection well to form a water-insoluble gel.

In the conventional method, since chemicals are injected from the same well, whether it is an injection well or a production well, a water-insoluble gel is created near the well. This has the disadvantage of impairing injection properties and clogging the vicinity of production wells.

In contrast, in this method, the water-soluble cationic polymer injected from the production well is selectively injected into the high permeability area and adsorbed. Thereafter, the water-soluble anionic polymer injected from the injection well also breaks through in the high permeability layer and is infiltrated earlier than the low permeability layer, so the water-insoluble gelation reaction occurs in the high permeability layer far from the vicinity of the production well. We will proceed with the penetration rate part.

Therefore, without causing gelation near injection wells or production wells, the gelation reaction occurs selectively only in the high permeability layer, and by lowering the permeability, the oil layer can be efficiently adjusted. It is possible to solve the problem of impairing injection efficiency and productivity near the well.

The present invention will be explained in detail below.

Specific examples of cationic water-soluble polymers used in the present invention include ethyleneimine polymers, condensation polymers of epichlorohydrin and dimethylamine (some of which also contain diamines, triamines, and polyepoxies). ), dimethyldiallylammonium chloride polymer, dimethylaminoethyl methacrylate methyl chloride polymer, dimethylaminoethyl acrylate methyl chloride polymer, dimethylaminopropylacrylamide polymer, and copolymers of one or more of these with acrylamide It is. These may be used alone or in combination.

The molecular weight and concentration of the cationic polymer injected into the oil layer largely depend on the properties of the polymer used and the geological formation to be treated, but the molecular weight is generally 1.000 or more, preferably 5.000 or more. Concentration is 10ppm ~ 10%,
Preferably it is 10 ppm -0.1%.

The anionic water-soluble polymer used in the present invention is a water-soluble polymer with a molecular weight of 106 or more, and specific examples include natural polymers such as xanthan gum, hydrolyzed polyacrylamide, and acrylamide and acrylic acid, methacrylic acid, and vinylbenzene. It is a polymer or a copolymer of two or more of sulfonic acid, maleic anhydride, etc., and the molecular weight is preferably 5 x 10" or more. The concentration of the anionic polymer when preparing the aqueous solution is determined by It depends largely on the permeability of the stratum, but the range is 10 ppm to 1
%.

The forms of the polymers used for these include powder emulsions, aqueous solutions, etc., and any form may be used. Furthermore, a conventional dissolving device suitable for the form of the polymer is sufficient.

Furthermore, other chemicals such as biocide, pH adjuster, stabilizer, surfactant, etc. may be used as necessary.

As an oil recovery method, first, an aqueous cationic polymer solution is injected from an injection well or a production well.

The amount of cationic polymer to be treated varies depending on the stratum, but it is desirable to inject 10% or more, preferably 30% or more of the pore volume of the targeted high permeability layer. The optimum amount is determined by testing on actual reservoir cores. The cationic polymer solution has low resistance during injection, and is therefore efficiently injected with high permeability. After injecting the water-soluble cationic polymer, it is decided whether to flush with brine or the like depending on the nature of the oil layer.

Wells that have already been treated with anionic polymers by polymer flooding etc. are pretreated by flushing with brine etc. from the production well to prevent clogging of the oil layer.

Next, an aqueous solution of anionic polymer is injected from the injection well.

It is desirable to inject the water-soluble anionic polymer aqueous solution so that the amount of anions is greater than the amount of cations in the cationic polymer initially injected. Further, polymer flooding is normally performed subsequently, but in that case, it is desirable to inject a water-soluble anionic polymer for polymer flooding and then proceed to polymer flooding continuously.

The solution of anionic polymer preferentially enters the high permeability layer and comes into contact with the previously treated cationic polymer (which has also been injected into the high permeability layer). Whereas anionic polymers have weak adsorption properties and are easily washed off, cationic polymers have a high adsorption property for rock debris and are retained well, so anions that come into contact with them react and form a water-insoluble gel efficiently. It often generates and reduces the permeability of high permeability layers. The above steps occur continuously within the stratum, improving the permeability of the oil layer and recovering oil.

[Examples] The present invention will be further explained with reference to Examples below, but the present invention is not limited in any way by the description of the Examples below.

Examples 1 to 3, Comparative Example 1 Berea 5and with a diameter of 2.5 cm and a length of 3 cm
Each solution shown in Table 1 below was flowed through a core of 5tone (permeability: about 500 md) according to the following procedure at a flow rate of 2 m/day to examine changes in permeability.

(1) Inject brine (0.1 wt% NaCI aqueous solution) and measure permeability (K w ).

(2) Inject 10 void volumes of cationic polymer solution (100 ppm).

(3) Inject 6 void volumes of brine.

(4) Anionic polymer (hydrolyzed polyacrylamide) solution (100 ppm) is injected in an amount of 10 pore volumes from the opposite direction.

(5) Inject brine and measure permeability (Kw).

The obtained permeability reduction coefficient (value obtained by dividing Kw before treatment by Kw after treatment) is shown in Table 1.

In Comparative Example 1, the anionic polymer was injected in Step 2 and the cationic polymer solution was injected in Step 4 using the same polymer as in Example 1.

Examples 4 to 5, Comparative Example 2 Berea 5and with a diameter of 2.5 cm and a length of 15 cm
Each solution shown in Table 2 below was flowed through a 5 tone (permeability: 500 md) core at a flow rate of 2 m/day according to the following procedure to examine changes in permeability.

(1) Inject brine (0.1 wt% NaCl aqueous solution) and measure permeability (K w ).

(2) Cationic polymer solution (200 ppm or 40
0 ppm) at a volume of 0.5 void volume.

(3) Inject 1.0 void volume of brine.

(4) Anionic polymer (hydrolyzed polyacrylamide) solution (100 ppn+) is injected in an amount of 10 void volumes from the opposite direction.

(5) Inject brine and measure permeability (Kw).

The obtained permeability reduction coefficients are shown in Table 2.

In Comparative Example 2, an anionic polymer was injected in step 2, and a cationic polymer solution was injected in step 4.

Examples 6 to 7, Comparative Example 3 Parallel core test Berea 5 and 5 with permeability of 60 m d and 570 m d connected in parallel with diameter 2.5 cm and length 15 cm
Each solution shown in Table 3 below was flowed through the tone core at a flow rate of 2 m/day according to the following procedure, and the amount of liquid flowing out from the core was examined.

(1) Inject brine (0.1 wt% NaCI aqueous solution) and measure permeability (K w ).

(2) Add cationic polymer solution (200ppll) to 0.00%.
Inject 5 void volumes.

(3) Inject 1.0 void volume of brine.

(4) Anionic polymer (hydrolyzed polyacrylamide) solution (100 ppm) is injected in an amount of 10 pore volumes from the opposite direction.

(5) Inject brine and measure permeability (Kw).

Table 3 shows the ratio of the liquid amount of the 570 md core to the liquid amount of the 60 md core.

In addition, Example 7 is the case where the anionic polymer was injected from the same direction as the cationic polymer in Step 4, and Comparative Example 3
This is the case where an anionic polymer was injected in step 2 and a cationic polymer solution was injected in step 4.

Procedural amendment (voluntary) March 1991 Day

Claims (1)

[Scope of Claims] 1) An oil recovery method characterized by adjusting the permeability of the oil layer by bringing a water-soluble anionic polymer into contact with a geological formation that has previously adsorbed a water-soluble cationic polymer. 2) The oil recovery method according to claim 1, characterized in that the water-soluble cationic polymer is injected from a production well, and the water-soluble anionic polymer is injected from an injection well.