CN1088141C - Mixtures for enhanced oil recovery in oil reservoirs - Google Patents

Abstract

The invention is intended for use in the petroleum industry as a gelatinous agent during refining of the oil fields by means of flooding. The proposed mixture provides for increased recovery of the oil layers for a wide range of layer temperatures including the highest, by redistributing the filtration flows and increasing the conformance of the flooded layer. The basic components of the mixture are cellulose and water esters, whereby the cellulose esters are esters with a low critical dissolution point, used in addition to carbamide or thiocarbamide, or ammonium thiocyanate, or a mixture of these elements according to the following proportions (in molecular weight): ester with a low critical solution point (0.25 to 2.0); carbamide (2.0 to 20.0); thiocarbamide (0.5 to 2.0); ammonium thiocyanate (0.5 to 2.0); and water (the remainder). It is preferable to use methylcellulose or methyloxypropylcellulose as the cellulose esters with a low critical solution point.

Description

Mixtures for enhanced oil recovery in oil reservoirs

The invention relates to the oil exploitation industry and can be used to inject water into the oil layer in the oil field exploitation to improve the oil recovery rate of the oil layer.

existing technical level

There is known a kind of mixture that enhances oil recovery of oil formation, and the method is to utilize the mixture that contains water-soluble polymer and polyvalent metal salt to reduce the permeability of high permeability zone of oil formation [U.S. Patent No.3762476, 3833061 and 4018286, International Classification of Inventions MKμE21B43/24]. In the oil layer, the polymer forms a gel through multiple cations to create a suture-sealing effect. However, the gels formed are not always successfully injected into areas of the reservoir far from the working face. This is due to the gel formation time of the mixture being too short. The use of such mixtures requires a relatively high cost. In order to improve oil recovery in oil reservoirs, the most recent technical essence is a mixture containing water-soluble polymer methylcellulose and calcium chloride-type mineralized water [Inventor's Certificate A.C.CCCP N681993, International Invention Classification MKμE21B43/20, Books and Information δμ47, 1991]. In the case of oil recovery by injecting water into the oil layer in the oil field, the polymer mixture may enhance the oil recovery of the oil layer, which relies on increasing the water injection to surround the oil layer. At this time, the polymer forms a gel in the oil layer that can plug and seal Highly leaking oil reservoirs. However, the salts that make up the calcium chloride-type mineralized water mixture can greatly reduce and reduce the temperature and time at which the polymer (methyl cellulose) solution forms a gel, which may cause the mixture injected into the oil layer to have a large volumetric dosage. It only works on the nearby working area of the oil layer, and does not affect some distant areas of the oil layer. When the temperature is 70-90°C, the time for the injected composition to form a gel is 10-30 minutes, which makes it difficult to use the mixture in high-temperature oil formations.

Disclosure of invention

The main task of the present invention is to provide a gelling agent mixture that can enhance the oil recovery of oil reservoirs in a wide range of reservoir temperatures up to the highest temperature by using components that can increase the gel formation time The filling volume surrounded by the oil layer is increased by water injection.

The proposed task is solved by using cellulose esters and water in a mixture for enhanced oil recovery in oil reservoirs, using esters with a low critical melting point as cellulose esters, and supplementary addition of urea or sulfur Urea or ammonium thiocyanate or their mixture, according to the following corresponding proportions (% by weight) of each component:

Esters with low critical melting point 0.25-2.0

Urea 2.0-20.0

Thiourea 0.5-2.0

Ammonium thiocyanate 0.5-2.0

Water is the rest

Most suitably, methylcellulose or methoxypropylcellulose is used as the lower critical melting point ester. By means of redistribution of the filtered liquid flow and increasing the volume of the oil layer by water injection, it is possible to enhance the oil recovery of the oil layer. This possibility is based on the fact that the cellulose ester-water system with a low critical melting point can In the porous medium of oil, a gel is formed at the temperature of the oil layer.

The effects of adding urea, thiourea, and ammonium thiocyanate have common characteristics and illustrate the ability to modify hydrophobic interactions and hydrogen bonds in aqueous cellulose esters. In the presence of these additives, the structure of water and the ability of water to solvate (solubilize) cellulose esters are changed, thereby improving the solubility of cellulose esters at high temperatures.

The concentration of methylcellulose or methoxypropylcellulose in the gel mixture is in the range of 0.25-2.0% by weight. Solutions with concentrations below 0.25% by weight form sols with low viscosity and low mechanical strength, while solutions with concentrations of 0.25 and higher form viscoelastically stable gels. Using a solution with a concentration higher than 2.0% by weight is not acceptable for the process because the initial viscosity of the mixture is too high.

The concentration of urea in the gel mixture ranges from 2.0 to 20.0% by weight. Good results cannot be obtained at lower concentrations because the temperature and gel formation time cannot be increased compared with methylcellulose; while at higher concentrations it increases the time to reach a high-viscosity gel.

The concentrations of thiourea and ammonium thiocyanate range from 0.5 to 2.0% by weight. At lower concentrations, good effects cannot be obtained, and increasing the concentration is not economically justified.

Brief description of the drawings

Fig. 1 shows the dependence of the gel formation time of 1% methylcellulose solution on the urea concentration at temperatures of 60°C, 70°C and 90°C.

Figure 2 illustrates the dependence of the gel formation temperature of a 1% methylcellulose solution on the concentration of thiourea (curve 1) and on the concentration of ammonium thiocyanate (curve 2).

Figure 3 is a graph illustrating the effect of urea on cellulose ester solutions in fresh fresh water (curve 1 for methyl cellulose, curve 2 for methoxypropyl cellulose) and in late Cretaceous Cyromantic water (curve 3 ) The effect of gel formation temperature.

Figures 4 and 5 illustrate the redistribution of filtrate flow and oil resurge after injection of various gel-forming mixtures in a heterogeneous reservoir model of varying permeability (leakage).

embodiment of the invention

The rheological properties research method and the determination of the gel formation temperature of the gel mixture were carried out using a vibratory viscometer with a tuning fork sensor and a thermostat, the detailed method is as follows:

Place 50 ml of the mixture to be studied into a constant temperature measuring cell. The probe of a tuning fork sensor was inserted into the solution and placed in a thermostat with a heating rate of 1.2°C/min. Viscosity values were recorded while heating from 20°C to 90-95°C.

Use distilled water as the calibration liquid. Upon heating, the viscosity of the solution gradually decreases from 7.3-104 mPa s (mPa s) to 1.7-33.6 mPa s, and then increases to 172-745 mPa s due to the formation of a gel , this viscosity increase is associated with gel formation and is characteristic of aqueous solutions of cellulose esters with low critical melting points. The viscosity of this mixture at 20°C is recorded, followed by the lowest viscosity of the solution and the viscosity of the gel formed.

The results of the study on the rheological properties, temperature and time of gel formation are listed in the table.

The effectiveness of the proposed mixture according to the invention was evaluated on the basis of the results of studies on gel-forming mixtures in a filtration study set-up through a model of a heterogeneous oil reservoir composed of oils with different degrees of penetration (leakage) Consists of two parallel cylindrical towers (pillars) (each with a common entrance and separate exits). Reservoir loose accumulation models with a permeability range of 2.229-4.676 micron ² (mcm ² ) were used, made from crushed oil-laden drill core material. The preparation of oil and core material was carried out according to standard methods used by the petroleum sector. Begin to drain the oil from both columns until the resulting sample is 100% full of water. During the process of expelling oil, the pressure and temperature at the inlet and outlet of the two columns, the volume of oil and water expelled from each column are measured at certain time intervals. According to the obtained data, calculate the fluidity or mobility of various liquids K/μ, micron ² /(mPa·s), where K is the permeability of the liquid model, μ is the viscosity of the liquid and the rate at which oil is squeezed out by water Crowding coefficient K _B , %. After the oil is squeezed out by the water, the ingredients of the gel-forming mixture are simultaneously injected into the two columns, pushed to a certain distance with water, and kept at a constant temperature in the oil reservoir temperature for a certain period of time to form a gel.

Then, continue to press into the water and after a certain period of time, measure the temperature, pressure, and the volume of oil and water discharged at the inlet and outlet of each column. From this data, the fluidity or mobility of the liquid and the absolute displacement coefficient for oil displacement by the gel mixture and water are calculated.

A lower volume of the gel mixture is injected into the lower permeable columns than the higher permeable columns. After injection of the gel-forming mixture into the reservoir model and formation of the gel, a redistribution of the filtrate flow occurs with oil make-up extrusion.

Give the following examples of gel mixtures

Embodiment 1 (according to prototype)

Add 10.0 grams of methylcellulose to 240.0 grams of hot (60-90°C) fresh fresh water and mix carefully. Add 250.0 grams of fresh cold water to the obtained suspension, and stir for 1-2 hours until a uniform solution is obtained, then add 500.0 grams of model oil layer water (composed of: NaCl2 17.5 g/L; _CaCl 20.0 g/L; MgCl ₂ 10.0 g/l). The resulting gel mixture contained 1.0% by weight of methylcellulose in water with a salinity of 65.0 g/l. The temperature and time of gel formation, the viscosity value of the mixture obtained, the minimum viscosity of the mixture and the viscosity of the gel are listed in the table (order N1).

Embodiment 2 (according to prototype)

A model mixture was used as mineralized water (composition: NaCl 91.1 g/l; CaCl ₂ 30.2 g/l; MgCl ₂ 8.7 g/l). The results of the study are shown in the table (rank N2).

Example 3

10.0 g of methylcellulose, 200.0 g of urea were added to 100.0 g of hot fresh water, and after stirring, 190.0 g of fresh cold water was added to the resulting suspension and stirred until a uniform solution was obtained. Then 500.0 grams of the injection water form of Example 2 was added. The resulting gel mixture contained 1.0% by weight of methylcellulose and 20.0% by weight of urea in water with a salinity of 65.0 g/l. The results of the study are shown in the table (rank N3).

Example 4

10.0 g of methylcellulose, 200.0 g of urea were added to 100.0 g of hot fresh water, and after stirring, 190.0 g of fresh cold water was added to the resulting suspension and stirred carefully until a uniform solution was obtained. Then 500.0 g of model Late Cretaceous water (composition: NaCl 13.7 g/L, CaCl ₂ 1.3 g/L, MgCl ₂ 0.39 g/L, KHCO ₃ 0.27 g/L) was added. The resulting gel-forming mixture contained 1.0% by weight methylcellulose, 20.0% by weight urea in water with a salinity of 7.8 g/l. The temperature and time of gel formation, the viscosity values of the mixtures obtained, the minimum viscosity of the mixtures and the viscosity of the gels are shown in the table (rank N4).

Example 5

10.0 g of methylcellulose, 50.0 g of urea and 10 g of thiourea were added to 2000.0 g of hot fresh water. After stirring, 230.0 g of fresh cold water was added to the resulting suspension and mixed carefully until a uniform solution was obtained. Then add 500.0 g of the water model to be injected, its composition is: NaCl 74.0 g/L, CaCl ₂ 27.9 g/L, MgCl ₂ 8.1 g/L). The resulting gel-forming mixture contained 1.0% by weight methylcellulose, 5.0% by weight urea, 1.0% by weight thiourea, dissolved in water with a salinity of 55.0 g/l. The temperature and time of gel formation, the viscosity value of the solution, the minimum viscosity of the mixture and the viscosity of the gel are listed in the table (order N5).

Example 6

10.0 g of methylcellulose and 10.0 g of thiourea were added to 200.0 g of hot fresh water and after stirring 280.0 g of fresh cold water were added to the resulting suspension and stirred carefully until a homogeneous solution was obtained. Then 500.0 g of the injected water form of Example 5 was added, and the resulting mixture solution containing 1.0 wt. % methylcellulose and 1.0 wt. % thiourea was dissolved in water with a salinity of 55.0 g/l. The temperature and time of gel formation, the viscosity value of the solution and the minimum viscosity and the measurement results of the gel viscosity are listed in the table (rank N6).

Example 7

10.0 g of methylcellulose, 50.0 g of urea and 20.0 g of thiourea were added to 400.0 g of hot fresh water, and after stirring, 520.0 g of fresh cold water was added to the resulting suspension and stirred carefully until a homogeneous solution was obtained. The resulting mixture contained 1.0% by weight of methylcellulose and 5.0% by weight of urea and 2.0% by weight of thiourea. The temperature and time of gel formation, the viscosity value and minimum viscosity of the mixture and the measurement results of the gel viscosity are listed in the table (N7). Example 8

2.5 grams of methylcellulose and 20.0 grams of urea were added to 400.0 grams of hot fresh water, and after careful stirring, 577.5 grams of fresh cold water were added to the resulting suspension and further stirred to obtain a homogeneous solution. The mixture contained 0.25% by weight of methylcellulose and 2.0% by weight of urea. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the gel viscosity are listed in the table (order N8).

Example 9

5.0 g of methylcellulose and 20.0 g of urea were added to 400.0 g of hot fresh water, and after careful stirring, 575.0 g of fresh cold water were added to the resulting suspension and mixed to obtain a homogeneous solution. The mixture contained 0.5% by weight of methylcellulose and 2.0% by weight of urea. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the viscosity of the gel are listed in the table (position sequence N9).

Example 10

Inject 300.0 g of hot fresh water into 10.0 g of methylcellulose and 200.0 g of urea. After careful stirring, add 490.0 g of fresh cold water to the suspension and stir until a homogeneous solution is formed. The mixture contained 1.0% by weight of methylcellulose and 20.0% by weight of urea. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the viscosity of the gel are listed in the table (order N10).

Example 11

Into 20.0 grams of methoxypropyl cellulose and 100.0 grams of urea was injected 400.0 grams of hot fresh water, and after careful stirring, 480.0 grams of fresh cold water was added to the suspension and stirred until a homogeneous mixture was formed. The resulting mixture contained 2.0% by weight of methoxypropylcellulose and 10.0% by weight of urea. The measurement results are listed in the table (number N11).

Example 12

Into 10.0 g of methoxypropyl cellulose and 50.0 g of urea were injected 400.0 g of hot fresh water, after careful stirring 540.0 g of fresh cold water was added to the suspension and stirred until a homogeneous mixture was formed. The resulting mixture contained 1.0% by weight of methoxypropylcellulose and 5.0% by weight of urea. The measurement results are listed in the table (N12).

Example 13

400.0 g of hot fresh water were poured into 10.0 g of methylcellulose and 5.0 g of thiourea, stirred and then 585.0 g of fresh cold water were added to the prepared suspension. After careful stirring, a homogeneous mixture was obtained which contained 1.0% by weight of methylcellulose and 0.5% by weight of thiourea. The measurement results are listed in the table (N13).

Example 14

Into 10.0 g of methylcellulose and 5.0 g of ammonium thiocyanate were injected 400.0 g of hot fresh water, and after careful stirring, 585.0 g of fresh cold water was added to the suspension with stirring to obtain a homogeneous solution. The mixture contained 1.0% by weight of methylcellulose and 0.5% by weight of ammonium thiocyanate. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the viscosity of the gel are listed in the table (position sequence N14).

Example 15

Into 10.0 g of methylcellulose and 20.0 g of ammonium thiocyanate were injected 400.0 g of hot fresh water, and after careful stirring, 570.0 g of fresh cold water was added to the suspension with stirring to obtain a homogeneous solution. The mixture contained 1.0% by weight of methylcellulose and 2.0% by weight of ammonium thiocyanate. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the gel viscosity are listed in the table (position sequence N15).

Example 16

400.0 g of hot fresh water was injected into 10.0 g of methylcellulose, 50.0 g of urea and 20.0 g of ammonium thiocyanate, and after careful stirring, 520.0 g of fresh cold water was added to the suspension and stirred to obtain a homogeneous solution. The mixture contained 1.0% by weight of methylcellulose, 5.0% by weight of urea and 2.0% by weight of ammonium thiocyanate. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the viscosity of the gel are listed in the table (position sequence N16).

Example 17

400.0 g of hot fresh water was injected into 10.0 g of methylcellulose and 10.0 g of thiourea, and after careful stirring, 580.0 g of fresh cold water was added to the suspension with stirring to obtain a homogeneous solution. The mixture contained 1.0% by weight of methylcellulose and 1.0% by weight of urea. The temperature and time of gel formation, the viscosity value and minimum viscosity of the prepared mixture and the measurement results of the gel viscosity are listed in the table (rank N17).

Example of preparation of this mixture under industrial conditions

Example 18

10.0 kg of methylcellulose and 20.0 kg of thiourea are charged in a container to prepare a mixture, 470.0 kg of hot water is supplied to it by a steam heating device, stirred by a suction pump combination device, and supplied to the container. Add 500.0 kg of fresh cold water and use the pump-container-pump system circulation method to stir until a uniform solution is obtained. The resulting mixture contained 1.0% by weight of methylcellulose and 2.0% by weight of thiourea. Thereafter, the mixture is pressure-injected into the well using a pump complex. The mixture ingredients are propelled into the oil layer with the injected water.

In order to study the filtration properties of the mixture proposed by the present invention, two mixtures were used: one mixture contained 1.0% by weight of methylcellulose, 5.0% by weight of urea and 1.0% by weight of thiourea, which were dissolved in g/l of water (Figure 4) and another mixture containing 1.0 wt% methylcellulose, 0.5 wt% thiourea, dissolved in fresh water (Figure 5). The permeability (leakage) of the column reaches 20.4 times for the first mixture (Fig. 4) and 4.2 times for the second mixture (Fig. 5). The injection of the various mixtures is indicated by dotted lines in Figures 4 and 5. The dosing values for the gel-forming mixture into the lower permeation column were 0.009 and 0.129 interstitial volumes, and the dosing values for the gel-forming mixture into the higher permeation column were 0.27 and 0.259 interstitial volumes, respectively. The fluidity (mobility) of the liquid before the mixture is injected in the low-permeability column is 0.035 micron ² /(mPa·s) (Fig. 4, curve 1) and 0.163 micron ² /(mPa·s) (Fig. 5 Curve 1); and in the hypertonic column, it is 1.0 micron ² /(mPa·s) (Fig. 4, curve 2) and 0.7 micron ² /(mPa·s) (Fig. 5, curve 2). After the gel is formed at the reservoir temperature when pressed into the water, the gel in the low-permeability column is flushed. The fluidity (mobility) of the liquid after injection is 0.038 micron ² /(mPa·s) (Fig. 4, curve 1) and 0.1 micron ² /(mPa·s) in the low-permeability column (Fig. 5, Curve 2), while in the hypertonic column it is 0.02 micron ² /(mPa·s) (Fig. 4, curve 2) and 0.001 micron ² /(mPa·s) (Fig. 5, curve 2), that is The permeability in the low-permeability column remains at the level before injection, while the permeability in the high-permeability column is reduced to a factor of 50-700. In this case, a redistribution of the filtrate flow takes place - the liquid filtration is essentially through the low-permeability column, which causes a supplementary displacement of oil (Fig. 4, curves 3, 4; Fig. 5, curve 3 ). In Figures 4 and 5 are presented the results of a study of the filtration properties and oil displacement capabilities of the gel-forming mixtures of the present invention. industrial applicability

In this way, with the mixture proposed by the invention, it is possible to generate a redistribution of the filtrate flow in the oil formation, as a result, increasing the fill-to-enclose factor of the oil formation by a factor of 1.6-2.3 by injecting water. Replenishment washes out remaining oil as filtrate flow is redistributed. The increase in oil extrusion coefficient or oil discharge rate is 5-12%. Compared with the prototype using 11-43 ℃, it can increase the gel formation temperature and increase the gel formation time by 2-100 times, which may expand the application field of the mixture of the present invention, especially, it can be used for high temperature oil reservoirs, typical , for example for West Siberian oil fields.

surface bit sequence Cellulose ester Salinity Additive weight% Gel formation temperature ℃ Viscosity, MPS Gel formation time minutes at the following temperature name Concentration weight 1% g/l urea Thiourea Ammonium thiocyanate solution viscosity Minimum Solution Viscosity gel 60℃ 70°C 90°C 1 prototype 1 123.8 - - - 38 54.8 29.2 640 25 20 10 2 prototype 1 65 - - - 36 64 21.2 681 20 15 10 3 Methylcellulose 1 65 20 - - 56 90.3 33.6 670 65 45 25 4 Methylcellulose 1 7.8 20 - - 74 64 16.8 660 1440 110 50 5 Methylcellulose 1 55 5 1 - 74 102 26 600 1440 120 50 6 Methylcellulose 55 - 1 - 49 50.4 30.3 380 50 35 20 7 Methylcellulose 0.25 0.001 5 2 - 72 56.3 15.2 676 1440 95 45 8 Methylcellulose 0.5 0.001 2 - - 65 7.3 1.7 396 480 80 45 9 Methylcellulose 1 0.001 2 - - 63 27 3.6 388 130 60 35 10 Methylcellulose 1 0.001 20 - - 79 50.4 11.6 172 1440 190 65 11 Methylcellulose 1 0.001 10 - - 73 104 19.4 635 1440 110 50 12 Methylcellulose 1 0.001 5 - - 72 20.3 4.4 222 150 55 13 Methylcellulose 1 0.001 - 0.5 - 67 51.8 21.2 310 170 75 40 14 Methylcellulose 1 0.001 - - 0.5 62 47.6 21.2 745 150 70 35 15 Methylcellulose 1 0.001 - - 2 62 47.6 21.2 745 150 70 35 16 Methylcellulose 1 0.001 5 - 2 65 44.9 21.2 635 240 80 40 17 Methylcellulose 1 0.001 - 1 - 68 53.3 16.8 159 210 85 40 18 Methylcellulose 1 0.001 - 2 - 70 67.2 13.7 600 240 75 35

Claims (2)

1. A mixture based on cellulose esters and water to enhance oil recovery in oil reservoirs, characterized in that as cellulose esters, use esters with a low critical melting point and supplement at least urea, or thiourea, or Ammonium thiocyanate, or their mixture, each component according to the following proportions, % by weight: Low critical melting point ester 0.25-2.0 Urea 2.0-20.0 Thiourea 0.5-2.0 Ammonium thiocyanate 0.5-2.0 Water is the rest 2. The mixture according to claim 1, characterized in that the low critical melting point esters as the mixture contain methylcellulose or methoxypropylcellulose.

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