JPH0410557B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an injection fluid used in forced oil recovery (EOR), and relates to a polymer composition for oil recovery that improves oil recovery with a small amount of use. Conventional Technology Oil extraction technology has evolved through three major stages to date. The first stage is currently called the primary recovery method, in which oil is recovered as it self-gushes using the natural energy of the oil layer, and the recovery rate is 1/1 of the reserves.
It is said to be around 3. The second stage is called the secondary recovery method, in which water or gas is artificially injected from the ground into oil fields where the artesian ability has diminished to push out the oil. Depending on these recovery methods, oil that exists as oil droplets in the pores of reservoir rocks, oil that adheres to the rock surface as an oil film, and oil that exists in areas that do not come into contact with gas or water at all in secondary recovery methods are recovered. It is thought that 1/3 to 2/3 of the crude oil remains underground, remaining unrecovered. Secondary recovery methods using pressurized water or pressurized gas prevent (1) the injected fluid from avoiding low permeability layers or regions, (2) fingering, and (3) high viscosity crude oils. (4) Channeling through cracks, etc. are said to be the causes of low recovery rates. Therefore, in order to further improve the oil recovery rate, it is considered to increase the flow resistance of the injection water, and it is known that a polymer aqueous solution is used as a means for this.
Polyacrylamide is used as a synthetic polymer, and xanthan gum is used as a biopolymer. The third stage is the technology to recover this residual oil and is called Enhanced Oil Recovery (EOR). The present invention relates to an EOR method. Problems to be Solved by the Invention As mentioned above, it is already known that polyacrylamide can be used to increase the flow resistance of injection fluid, but the modification of the acrylamide polymer itself has not yet been sufficiently studied. . The present invention aims to provide an oil recovery agent that exhibits even better injection fluid properties by adding a small amount of additives to an acrylamide polymer. Means/effect for solving the problems The present invention consists of: 1. 100 parts by weight of an acrylamide polymer;
Mercaptobenzimidazole or its salt 0.5
An improved petroleum recovery polymer composition of resistance factor and residual resistance factor consisting of ~2 parts by weight, and 100 parts by weight of an acrylamide polymer, 0.5 parts by weight of 2-mercaptobenzimidazole or its salt.
2.0 parts by weight and 0.05 to 5.0 parts by weight of a thiourea. Next, the composition of the oil recovery polymer composition of the present invention will be explained in more detail. In the aforementioned oil recovery method using pressurized water, it has been known for a long time that the mobility ratio between the displacement fluid, ie, pressurized water, and the fluid to be replaced, ie, crude oil, greatly influences the recovery rate. The mobility ratio (M) is defined as follows. M = (Kw / μw) / (K ₀ / μ ₀ ) ... (1) where, Kw is the relative permeability of water at the saturation rate of immobile oil K ₀ is the relative permeability of oil at the saturation rate of immobile water μw is The viscosity of water μ ₀ is the viscosity of oil. In the case of normal pressurized water, M has a very high value of 10 to 30, and water is more mobile than oil, which is associated with a low oil recovery rate. If M is lowered to 1 to 2 by some means, the action of pushing out the oil will be performed smoothly. In the polymer attack method, the water is replaced with a polymer solution, and in order to know the performance of the polymer solution in reducing M, the resistance factor RF is measured. RF = (Kw/μw)/(Kp/μp) ...(2) where, Kp is the relative permeability of the polymer solution at the fixed oil saturation rate μp is the viscosity of the polymer solution This RF is the concentration of the polymer, the molecular weight of the polymer It is easily understood from equation (1) and its explanation that a large value of RF is preferable as a solution for oil recovery, although it is influenced by the properties of the solvent and the properties of the solvent. Another feature of the acrylamide polymer solution is that once the polymer solution is passed through the rock, it semi-permanently reduces the permeability of the rock. The residual resistance factor RRF indicates this decrease in permeability. RRF=(Kw/μn) (before passing through polymer solution)/(Kw/μn)
w) (After passing through the polymer solution) ...(3) As this RRF increases, the permeability of the rock after passing through the polymer solution decreases.In principle, the crude oil layer is pushed by the polymer solution layer, and the polymer solution layer is This is a favorable phenomenon for the polymer mining method, which extracts crude oil by pressing layers. In addition, the above equations (2) and (3) are as follows: K/μ=QL/A・ΔP However, since A: Core cross-sectional area L: Core length Q: Flow rate, the following (4) and It becomes as shown in equation (5). RF=QwL/A・ΔPw・A・ΔPp/QpL = (Qw/ΔPw) (ΔPp/Qp) = (ΔPp/Qp)/(ΔPw/Qw) ……(4) RRF=(Qw/ΔPw) (ΔPw '/Qw') = (ΔP'w/Qw')/(ΔPw/Qw)...(5) The inventor determined the composition of the oil recovery polymer composition of the present invention to be within a specific range based on these two resistance factors. If the amount of 2-mercaptobenzimidazole (sometimes abbreviated as MBI) or its salt added is less than 0.5 part by weight in terms of MBI, the above-mentioned The effect of increasing the two resistance factors cannot be expected, and the amount of MBI or its salt added is 2.0 in terms of MB.
If the weight percentage is exceeded, the two resistance factors mentioned above will be reduced. That is, the two resistance factors have maximum values within the above-mentioned limited range. Furthermore, by adding thioureas in the range of 0.05 to 5.0 parts by weight per 100 parts of the acrylamide polymer to the composition of MBI or its salt within the above range, the above two resistance factors can be further improved. However, addition of thioureas outside these ranges actually decreases the two resistance factors. In the present invention, the acrylamide polymer includes all water-soluble polymers containing an acrylamide component. Specifically, copolymers of acrylamide and acrylic acid (salt), methacrylic acid (salt), 2-acrylamide-2-methylpropanesulfonic acid (salt), etc., or water-soluble anionic polymers of these methacrylamide within the range that does not impair the properties of the
Polymers containing acrylonitrile, dimethylaminoethyl methacrylate tertiary salt, quaternized product, acrylic acid lower alkyl ester, etc. Furthermore, it is not limited to those based on so-called copolymerization reactions, but also includes those in which the amide group is converted to other functional groups by various chemical reactions after polymerization, such as those in which the amide group is hydrolyzed with an alkali or methylolated. It also includes mixtures of two or more of the above polymers. Further, the apparent degree of polymerization is preferably 10,000 or more. Next, 2-mercaptobenzimidazole or a salt thereof is a water-soluble compound represented by the following general formula. (However, X represents hydrogen, an alkali metal, or ammonium.) When X is hydrogen, it has poor solubility, so it is usually used in the form of sodium salt, potassium salt, or ammonium salt. In addition, the thioureas referred to in the present invention have the following general formula:

[expression] or

[Formula] (In the formula, R ¹ and R ² represent hydrogen or an organic group consisting mainly of carbon and hydrogen, and R ³ represents an organic group mainly consisting of carbon and hydrogen.) A compound having at least one. For example, such thioureas include thiourea, N,N'-diphenylthiourea, diortho-tolylthiourea, ethyleneurea, and the like. Furthermore, the polymer composition of the present invention is not limited to the case where the acrylamide-based polymer, MBI or its salt, and thiourea are mixed to form a solid state, but also when the above three components substantially coexist in the state of use. For example, it may be in the form of a solution, slurry, gel, etc. As for the method of mixing these three, any commonly known method can be employed. Therefore, the concentration at which the polymer composition of the present invention exhibits an effect on oil recovery is about 100 ppm to 50,000 ppm aqueous solution, and a concentration of 100 ppm to 10,000 ppm is particularly preferred. Example: A polymer consisting of 80 mol% acrylamide and 20 mol% sodium acrylate, with a molecular weight of approximately
15000000 acrylamide-based polymer with salt
Using salt water (solvent) containing 0.14 g/, calcium chloride anhydride 0.18 g/, the concentration of acrylamide polymer in the solution was adjusted to 300 ppm,
Specified amounts of MBI and thiourea were added and dissolved with stirring to obtain 10 samples with different compositions as shown in Table 1. Core tests were conducted on these polymer composition solution samples using Berea sandstone with a permeability of 900 to 1000 millidarcy as a model of oil reservoir rock. For each sample, flow the fluid into a new core in the following order, find the flow rate Q and the pressure difference ΔP before and after the core, and (4)
The resistance factor RF and the residual resistance factor RRF were determined using equations (5) and (5). Note that the liquid temperature was maintained at 25°C±1°C. Measurement order Liquid Flow rate Differential pressure 1 Solvent Qw ΔPw 2 Sample Qp ΔPp 3 Solvent Q′w ΔP′w RF=(ΔPp/Qp)/(ΔPw/Qw) ……(4) RRF=(ΔP′w/Qw′) /(ΔPw/Qw)...(5) The obtained results are shown in Table 1.

【table】

[Table] Effects of the Invention According to the polymer composition for oil recovery of the present invention, it is possible to reduce the amount of polyacrylamide used in conventional polymer flooding methods or to improve the oil recovery rate. The economic effects are extremely large.

Claims (1)

[Scope of Claims] 1. 100 parts by weight of an acrylamide polymer, and 2-
Mercaptobenzimidazole or its salt 0.5~
An improved oil recovery polymer composition of resistance factor and residual resistance factor comprising 2 parts by weight. 2 100 parts by weight of acrylamide polymer, 0.5 to 2-mercaptobenzimidazole or its salt
2.0 parts by weight and 0.05 to 5.0 parts by weight of thioureas.