EA039711B1 - Method for oil reservoir development - Google Patents

Abstract

The invention relates to oil and gas production industry, in particular, to a method for increasing the oil recovery of a field using thermal, chemical and gas techniques. The objective of this invention is to improve the efficiency of the method through the use of the formation power potential and low cost chemicals, to increase the displacement factor and to ensure a safe process execution. The objective is achieved by that in this method for oil reservoir development, comprising successive injection of aqueous solutions of potassium salt and acid to a well, prior to injection of the acid aqueous solution to a formation, light oil or gas condensate is injected into this formation; and after the injection of the acid aqueous solution air is injected with further pushing with water, wherein a sulfuric acid aqueous solution is used as acid aqueous solution, and a 16% potassium bichromate aqueous solution is used as potassium salt aqueous solution.

Description

The invention relates to the oil and gas industry, in particular to a method for increasing oil recovery of a field using thermal, chemical and gas methods.

There is a known method for enhancing oil recovery of a field, including thermal gas treatment of the formation by successively injecting oxygen-containing gas and water into the formation in fields with a formation temperature of 90-200°C, and after injecting oxygen-containing gas and before injecting water, a solution of sodium bicarbonate or potassium or their is pumped into the formation. mixtures with a concentration of 20-80 g/l [1].

The disadvantage of this method is its low efficiency for low-temperature formations.

A known method of developing an oil field, including in-situ oxidation reactions by pumping heated water and air into the reservoir through an injection well with a water-to-air ratio of 0.006-0.015 m ³ /nm ³ , and the temperature of the productive formation is adjusted to 70200°C [2].

The disadvantage of this method is the low efficiency as a result of heat loss during the injection of heated water, especially in deep productive formations.

Closest to the proposed invention is a method of thermochemical treatment of the bottomhole zone of a well, including sequential injection into the formation of an oxygen-containing organic compound, an aqueous saturated solution of sodium or potassium nitrate and a 30-35% aqueous solution of hydrochloric acid, and dimethyl and acetic esters, methyl and ethyl alcohols, glycerin, acetone, etc. [3].

The disadvantages of this method are the low depth of formation treatment, low displacement efficiency, multicomponent nature and the associated multi-stage process, as well as high corrosiveness of the system components and products of its thermochemical transformation. The efficiency of this method is also low, since, in addition to the use of expensive reagents, the disadvantage is that hydrochloric acid may not completely react with nitrates and insufficient heat will be released to form the required amount of oxygen from oxygen-containing substances. In this case, the heating of the bottomhole zone will be short and weak, insufficient to transfer asphalt-resinous substances into a fluid state, and with a limestone reservoir, unreacted hydrochloric acid will destroy, in addition to clogging cement, the filter channels themselves.

The objective of the invention is to increase the efficiency of the method by using the energy potential of the reservoir and inexpensive chemicals, increasing the displacement efficiency and ensuring the safe implementation of the process.

The problem is solved by the fact that in the method of developing an oil deposit, which includes successive injection of aqueous solutions of potassium salt and acid into the well, light oil or gas condensate is pumped into the formation before the aqueous acid solution is injected, and after the aqueous acid solution is injected, air is then pushed through with water, in this case, an aqueous solution of sulfuric acid is used as an aqueous solution of an acid, and a 16% aqueous solution of potassium dichromate is used as an aqueous solution of potassium salt.

The essence of the method lies in the fact that in order to be able to carry out the process of thermal gas treatment, which consists in low-temperature oxidation of oil as a result of injection of oxygen-containing gas into the formation, in fields with low formation temperatures, reagents capable of entering into an exothermic reaction with the release of a large amount of heat are first pumped into the well. In the proposed method, an aqueous solution of potassium dichromate K ₂ Cr ₂ O ₇ , which has strong oxidizing properties, is pumped into the injection well. After potassium bichromate, light oil or gas condensate is injected into the reservoir, which serves as a separator and prevents premature mixing of the injected solutions of potassium bichromate and sulfuric acid. Also, the injection of the separator contributes to a deeper penetration of solutions into the formation.

It is known that the reservoir near the injection well contains a small amount of oil, and in most cases only residual oil. This reduces the intensity of oxidative reactions and the release of a large amount of heat and reaction products in this zone. The injection of light oil or gas condensate as a separator increases the efficiency of oxidative reactions between potassium bichromate and hydrocarbons, contributing to the release of large volumes of heat and reaction products.

As a result of the reaction of reservoir oil and light oil or gas condensate injected as a separator with an oxidizer (potassium bichromate solution), oil attaches oxygen to itself and peroxides are formed. The process occurs by radical mechanisms.

The radical addition reaction mechanism and the oxidation mechanism are as follows:

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RH + Ο-Ο· -> R' + ΗΟΟ·

R+ + Ο-Ο-► ROO*

ROO* + R'H - ROOH + R'·

R + R' → R + R'

R^+ROO -> R'OOR

R'+ROO· -► R'OOR

ROOH RO + ΟΗ

Thus, in the first stage, the process is initiated to intensify oxidative reactions. For this purpose, an easily oxidizing agent is introduced into the well.

During the oxidation process, the formation of aldehydes, alcohols, acids, etc. occurs.

After that, sulfuric acid is pumped into the reservoir:

When potassium bichromate reacts with sulfuric acid, chromium anhydride is formed and heat is released. Chromic anhydride reacts with organic substances - alcohols, ketones, etc., which were formed during the cold oxidation of oil, which contributes to an additional increase in temperature. As a result of the exothermic reaction, a large amount of heat is released.

After that, air is pumped into the formation. The influx of oxygen present in the composition of the injected air into the reservoir, as well as the heating of the medium due to the heat released as a result of exothermic reactions, contribute to the enhancement of the oxidation process. As a result of oxidative reactions, a large amount of heat, light liquid hydrocarbons, hydrocarbon gases and carbon dioxide are released. At the next stage, the oxidation process grows, as a result, the amount of gases formed in the reservoir increases and the pressure rises. Thermal and oil-displacing rims are formed in the reservoir. There are phase transitions, physical and chemical changes in formation fluids and gases. Additional pressure drop contributes to an increase in the process of oil displacement.

The rate and temperature of oxidation are directly proportional to the composition of hydrocarbons, the amount of mixture, humidity and concentration of oxygen molecules. The injection of sulfuric acid significantly reduces the activation temperature of the oxidation of potassium bichromate. Thus, the supply of air and the further entry of hydrocarbons into an exothermic reaction with oxygen provide heating of the porous medium to the temperature at which the spontaneous in-situ oxidation process begins.

Considering that, unlike in-situ combustion, oil oxidation processes occur at temperatures up to 250°C, the release of harmful products of deep thermal-oxidative destruction of oil, such as sulfur oxides, is not observed.

Thus, the injection of chemical reagents ensures the start of the oxidation process, its uniform distribution in the bottomhole zone, the expansion of the area that ensures the start of the process, and the alignment of the front of movement of the exothermic reaction zone.

Oxygen, which is part of the air pumped in afterward, enters into a low-temperature oxidative oil reaction. The thermal and oil-displacing fronts formed during the oxidation process contribute to a significant increase in the oil recovery of the reservoir. The water injected next creates a moving zone of exothermic reactions in the formation.

As a result of formation hydrocarbons oxidation by oxygen present in the injected air, CO ₂ , CO, N ₂ gases, a wide fraction of light hydrocarbons and water are formed in the formation. The generated gases create an additional pressure gradient in the formation, part of the gases dissolve in the formation fluids, changing the viscosity, pH, surface tension of the medium in the direction of increasing the process of oil displacement from the formation to the production wells. When the temperature reaches above 65°C, all the oxygen pumped into the formation is consumed in spontaneous in-situ oxidation reactions, which ensures the safety of the thermal gas treatment process. At low reservoir temperatures (below 60-65°C), as a result of heat loss in the reservoir, it is impossible to carry out the process of thermal gas treatment without additional heating of the medium.

The efficiency of the method is increased due to the use of the energy potential of the formation, low-cost chemicals, and the unlimited availability of injected air.

An increase in reservoir temperature contributes to an increase in oil mobility, a decrease in viscosity, and interfacial tension, which facilitates the movement of oil to production wells. Sulfuric acid injected into the reservoir, products obtained as a result of exothermic reactions, and an increase in the temperature of the medium contribute to the melting and washing of asphaltene-resin-paraffin deposits from the rock surface. The impact of the injected and resulting reactions of acids on the rock increases with increasing temperature, which leads to an increase in the permeability of the porous medium.

It should be noted that in the proposed method there is an additional stage, including the reaction of potassium bichromate with injected light oil or condensate, as well as with residual oil of the bottomhole zone, resulting in the formation of aldehydes, alcohols, acids, etc. This increases the

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The method uses a solution of potassium dichromate (GOST 2652-78), sulfuric acid (GOST 2184-2013), stable gas condensate (GOST R 54389-2011).

The method is carried out as follows. A section of the field with injection and production wells is selected for the implementation of the process, the technical condition of the well selected for injection is checked. A 16% aqueous solution of potassium dichromate, light oil or gas condensate, and an aqueous solution of sulfuric acid are sequentially pumped into the well. Following the reagents, air is injected into the formation in an amount of 30% of the pore volume. After that, water is injected into the reservoir.

The method has been tested in laboratory conditions.

Example 1

An aqueous solution of 16% potassium dichromate, light oil or gas condensate was poured into a flask equipped with a stirrer and a thermometer and stirred at room temperature (20°C). Then a solution of sulfuric acid was added to the mixture. The increase in the temperature of the mixture was observed and the time of the temperature increase was recorded. The results of the experiments are shown in table. one.

Table 1

experience number Potassium bichromate solution, ml U helminthic separator, ml Sulfuric acid solution, ml Mixture temperature, °C Temperature rise time, min one eighteen Light oil 20 2 168 46 2 17 Gas condensate20 3 203 59 3 sixteen Light oil 20 4 245 65 4 fifteen Gas condensate20 5 278 74 5 fourteen Light oil 20 6 302 83 6 thirteen Gas condensate20 7 275 97 7 Prototype 156 103

As a result of the addition of light oil or gas condensate to potassium bichromate, cold oxidation occurs. The addition of a sulfuric acid solution promotes the intensification of exothermic reactions and an increase in temperature. The maximum effect is obtained in experiments 4 and 5 with the addition of 14-15 ml of potassium bichromate, 20 ml of gas condensate or light oil and 5-6 ml of sulfuric acid solution. In this case, the temperature of the mixture rises significantly and reaches 300°C. Conducted experience on the prototype, where the value of the maximum temperature of the mixture reached 156°C, and the rise time was 103 min (table. 1).

Example 2

The method was tested on an experimental setup, including a linear reservoir model, devices for separating, measuring and sampling gas, oil and water. The length of the linear reservoir model was 1.2 m, the inner diameter was 0.04 m. The porous medium consisted of quartz sand. A model of a heavily watered formation was created. After that, a 16% potassium bichromate solution was pumped into the model under thermostating (at a temperature of 40°C), observing the proportions of the previous experiment, in an amount of 15% of the pore volume, then a sulfuric acid solution was pumped in in an amount of 5% of the pore volume. The first experimental study was carried out without a separator. In the second and third experiments, 20 ml of light oil was pumped between the reagents in one case, and gas condensate in the other. Some time after the injection of reagents, an increase in temperature is observed, which indicates the beginning of the oxidation process. Further, air is pumped into the model in an amount of 30% of the pore volume, which contributes to the intensification of oxidative reactions. Models close and observe the increase in pressure and temperature. Subsequently, water was again supplied to the input of the model and the displacement coefficient was determined. The experiments were also carried out in accordance with the prototype. The results are shown in table. 2.

table 2

experience number Initial displacement ratio „d. units Delimiter Tempe- temperature, °C Pressure, MPa Temperature rise time, h Final oil displacement factor, units Growth of displacement efficiency, % one 0.571 Is absent 145 0.40 7.0 0.747 17.6 2 0.548 light oil 208 0.60 6.7 0.743 19.5 3 0.553 gas condensate 212 0.62 6.1 0.750 19.7 4 by prototype 0.558 90 0.32 8.3 0.671 11.3

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As can be seen from experimental studies, in the case when the separator was not pumped into the model (experiment 1), the intensity of exothermic reactions is much lower. This can be seen from observations of the dynamics of pressure and temperature. The displacement ratio in this experiment is 17.6%. In experiments 2 and 3, carried out using a separator, after the injection of reagents, a greater increase in temperature and pressure is observed, the temperature reaches values above 200°C, and the pressure is above 0.6 MPa. The increase in the displacement efficiency in these experiments averaged 19.6%. Experience 4 was carried out in accordance with the prototype. In this case, the increase in the displacement efficiency was 11.3%.

Example 3

In the process of experimental studies given in example 2, samples of water and gas were taken and analyzed. The component composition of the gas, the pH of the water, and the corrosion rate were determined. The results are shown in table. 3.

Table 3

experience number The amount of CO2 in the composition of the gas sample, % The amount of SO2 in the composition of the gas sample, % Quantity О2 in the composition of the gas sample, % pH Corrosion rate, g/m ² hour one fifteen traces 0.01 7 0.01 2 20 — — eight 0 3 22 — — eight 0 4 ten 2 0.02 7 0.03

As the results of the analyzes showed, in the first experiment without the use of a separator, the amount of carbon dioxide formed is less than in the subsequent ones, there are traces of sulfur dioxide and a small amount of oxygen in the sample. These indicators indicate an insufficient rate of oxidative processes. The pH value in this run is 7 and the corrosion rate is 0.01 g/m ² -h. In experiments 2 and 3 with the use of a separator, the content of carbon dioxide in the composition of the sample increases, while sulfur dioxide and oxygen are absent, which indicates more efficient oxidative processes in the model of a porous medium. The pH of the medium also increases, and the corrosion rate is zero. The last experience 4 was carried out in accordance with the prototype. From Table. 3 shows that his results are not satisfactory.

Literature.

1. RU 2277632, Е21В 43/22.43/24, 2006.

2. A.s. USSR No. 1241748, E21B 43/24, 1996.

3. RU 2023874, E21B 43/24, 43/27, 1994.

CLAIM

Claims (1)

CLAIM A method for developing an oil deposit, which includes successive injection of aqueous solutions of potassium salt and acid into the well, characterized in that before injection of an aqueous solution of acid, light oil or gas condensate is pumped into the reservoir, and after injection of an aqueous solution of acid, air is then pushed through with water, while as an aqueous solution of acid, an aqueous solution of sulfuric acid is used, and as an aqueous solution of potassium salt, a 16% aqueous solution of potassium dichromate is used.