RU2277632C1 - Oil field recovery increase method - Google Patents

Abstract

FIELD: oil production industry, particularly to increase oil field recovery with the use of heat and gas treatment methods.

SUBSTANCE: method involves applying heat-and-gas action on formation by serially injecting oxygen-containing gas and water in formation of oil field having formation temperature of 90-200°C; injecting alkali bicarbonate solution of 20-80 g/l concentration into formation; injecting water. The alkali bicarbonate is sodium bicarbonate or potassium bicarbonate or mixture thereof.

EFFECT: increased oil recovery, increased efficiency of heat and gas action to oil fields at later or final development stage.

2 cl, 6 ex, 6 tbl

Description

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

State of the art

The essence of the method of thermogas exposure (TGV) is the low-temperature oxidation of oil in the reservoir by pumping oxygen-containing gases into injection wells. As a result of oil oxidation, a large amount of heat is released, carbon dioxide is formed, hydrocarbon gases and light liquid hydrocarbons are formed and evaporated from the residual oil. Thermal and oil displacing (carbon dioxide + mixture of gaseous and light liquid hydrocarbons) formed as a result of the oxidation process can significantly increase the degree of oil displacement from the reservoir. The prospects of the DVT method are associated with the high availability of the main reagent - air. Therefore, this method of exposure is particularly suitable for use in remote fields.

Most of Russia's large fields are entering or are in the late or final stages of development, which are characterized by high water cut of the produced oil. Moreover, the degree of oil recovery usually does not exceed 30-40% of geological reserves. Currently, there is the problem of developing new and improving well-known methods for increasing oil recovery at the late and final stages of development.

A known method for the implementation of DVT, including the creation of a thermal rim in the formation with the aim of heating the bottom-hole zone of the formation to the temperature of oil oxidation, followed by injection of a mixture of air and water (AS USSR No. 329306, 1972). The disadvantage of this method is the inefficiency in the conditions of deposits at a late stage of development.

A known method for the implementation of DVT, including the injection into the formation of heated water and air with a water-air ratio of 0.006-0.015 m ³ / nm ³ , the temperature of the reservoir being brought to 70-200 ° C (AS USSR No. 1241748, 1996). The disadvantage of this method is the inefficiency in the conditions of deposits at a late stage of development.

A known method for the development of oil deposits (RF patent No. 1464555,1996), the essence of which is the sequential injection into the formation of a fraction of light hydrocarbons as a solvent and a vapor-air mixture as an oxidizing agent. The disadvantage of this method is its low efficiency in the conditions of deposits at a late stage of development.

For the effective and safe implementation of the DVT method, it is necessary that the oil reservoir in the area of the producing well contain a sufficient amount of oil, which is the case if the field is at the initial stages of development. In depleted fields, formations in the area of injection wells contain only residual oil. Therefore, as a result of oxidation processes, a high temperature cannot develop and, as a result, a large number of active reaction products — carbon dioxide and low molecular weight hydrocarbons — are formed. The consequence of this is the low efficiency of the known technical solutions in the conditions of deposits located in the late and final stages of development.

The closest in technical essence is a method of developing an oil field, including the injection into the reservoir through an injection well of an oxygen-containing gas mixture and water (RF patent No. 2139421, 1999 - a known method). This method is not effective enough in the conditions of deposits located in the late and final stages of development.

Thus, there is a problem of increasing the efficiency of the thermogas method of increasing oil recovery, which will allow the use of hot water in conditions of oil fields that are in the late and final stages of development.

SUMMARY OF THE INVENTION

The technical result is an increase in oil recovery, ensuring the effective implementation of DVT in fields located in the late and final stages of development.

In a method of increasing oil recovery of a field, including thermogas treatment of the formation by successively injecting oxygen-containing gas and water into the formation, when using it in fields with a formation temperature of 90-200 ⁰ C, after injecting oxygen-containing gas and before injecting water, an alkali metal bicarbonate solution is injected into the formation with concentration of 20 - 80 g / l.

As the alkali metal bicarbonate, sodium or potassium bicarbonate or mixtures thereof are used.

As oxygen-containing gas, air or mixtures of air and oxygen with other gases are used.

For the preparation of bicarbonate solutions use industrial fresh water, water from oil fields, or a mixture thereof.

The method is carried out by sequential injection into the formation through injection wells of rims of oxygen-containing gases, an aqueous solution of bicarbonates and water.

The implementation of the invention

As a result of in-situ oxidation of oil, a significant amount of oxygen-containing reaction products (alcohols, carbonyl compounds, acids) and carbon oxides is formed, as well as heat. Among the products of in-situ transformation of an oxygen-containing gas, carbon dioxide is the most valuable, which is a highly effective oil-displacing reagent. The main reason for the lack of effectiveness of the known technical solutions and the known method is the low yield (calculated on absorbed oxygen) of the most effective oil oxidation product - carbon dioxide. In the known technical solutions and the known method, other products (except carbon dioxide and light hydrocarbons) of the oil oxidation reaction are also not used.

In the method proposed in the invention, as a result of sequential injection into the reservoir of oxygen-containing gas and a solution of alkali metal bicarbonate, the following processes occur:

1) Intra-layer oxidation of oil leads to the formation of a large number of oxygen-containing products, in particular carbon dioxide, organic acids, as well as heat.

2) Alkali metal bicarbonates are thermally unstable compounds, when heated, decomposing by the endothermic reaction with the formation of carbonates and carbon monoxide (TV):

where Me is an alkali metal ion, Q is the thermal effect of the reaction. Reaction 1 proceeds with heat absorption, i.e. more complete utilization of heat generated during the oxidation of oil.

3) The interaction of bicarbonates and carbonates of alkali metals with organic acids and esters (products of oil oxidation) leads to the formation of salts of carboxylic acids, which are effective surface-active substances (surfactants), as well as carbon dioxide:

2R ¹ COOR ¹¹ + Me ₂ CO ₃ + H ₂ O = 2 R ¹ COOMe + CO ₂ ↑ + 2 R ¹¹ OH (4)

In reactions 2-3, a significant amount of heat is also released.

Thus, the filtration of a solution of alkali metal bicarbonates through an oxidized oil zone results in the formation of highly effective oil-displacing agents - carbon dioxide and surfactants, heat generation during exothermic reactions, as well as more complete utilization of the heat of the oxidation reaction.

Carbon dioxide formed from bicarbonate is added to carbon dioxide formed as a result of in-situ oxidation of oil. An increase in the amount of carbon dioxide in the formation and its concentration in the gas phase will facilitate the transition to the so-called miscible displacement mode and, as a result, the growth of oil-displacing ability and the effectiveness of DVT.

Surfactants formed in the reservoir can be divided into two types: water soluble (formed from low molecular weight acids) and oil soluble (formed from high molecular weight acids). Water-soluble surfactants pass into the aqueous phase, reducing interfacial tension at the border with oil, which contributes to a more complete displacement of oil from the reservoir. A mixture of oil-soluble surfactants with other oxygen-containing oxidation products (alcohols, carbonyl compounds, esters), as well as resins, is an effective stabilizer of foam and inverse emulsions. The formation in the zone of oxidized oil of foam (from injected gases and released carbon dioxide) or reverse emulsion (from oxidized oil and water) leads to a decrease in the permeability of the formation areas subjected to DVT. Considering that oxygen-containing gas is filtered into the most permeable sections of the formation, a decrease in their permeability leads to a redistribution of filtration flows in the formation and the displacement of oil from poorly drained sections and layers.

In the known method and known technical solutions, most of the oxidation products are not involved in the processes of oil displacement, and a significant part of the heat is lost unproductive. In the proposed method, the task of the invention is solved - increasing the efficiency of the DVT method by using most of the products of in-situ oxidation of oil and more complete utilization of heat to increase oil recovery.

Example 1

To study the composition of oil oxidation products, a monometric installation based on an autoclave, for example, manufactured by PARR (USA), model 4842 is used. The autoclave is equipped with a glass liner to prevent contact of the reaction mixture with the metal surface of the autoclave, has a minimum of non-thermostatically controlled volumes, protective covers (coatings) made of inert materials (glass or Teflon) for a thermocouple pocket measuring the temperature of the reaction mass, and a mixing device.

The characteristics of the autoclave-based plant are as follows:

reactor volume (according to the passport) - 1 l;

the free volume of the reactor is 1.08 l,

a maximum working pressure of 1900 lbs / ⁱⁿ² (14 MPa);

maximum working temperature - 350 ° C.

The monometric installation also includes a high-pressure pump and a supply line system with shut-off valves, allowing during the experiment to supply an aqueous solution of alkali metal bicarbonate to the reactor with oxidized oil.

Samples of reservoir fluids (oil and water) of the field are prepared for experiments using generally accepted methods used in physicochemical and filtration experiments. The characteristics of water and oil are shown in Table 1. At the end of the experiment, a gas sample is taken from the autoclave into a high pressure sampler and analyzed for the content of components using a gas chromatograph.

Table 1 Characterization of degassed oil and associated water samples Fluid Density, kg / m ³ Viscosity at 20 ° С, MPa · s Oil 862 7.5 Water 1020 1,02

For chromatographic analysis of a gas sample for the content of basic gases (nitrogen, oxygen, carbon oxides), chromatographic columns of 3 m in length, 3.2 mm in diameter HayeSep Q (nitrogen, oxygen and CO) and 2 m in length, 3.2 mm in diameter are used MolSieve 5A (carbon dioxide). Analysis mode: carrier gas - helium, analysis temperature 40 ° С, thermal conductivity detector. The following chromatographic columns are used in series for the analysis of hydrocarbon gases:

1. 25% n-butyl maleic acid on chromosorb P AW (60-80 mesh), diameter 3.2 mm and length 8 m;

2.25% dipropionitrile on P AW chromosorb (60-80 mesh), diameter 3.2 mm and length 3 m.

Conditions for the analysis of hydrocarbon gases: carrier gas - helium, temperature 40 ° C, flame ionization detector.

It is possible to use other types of chromatographs and chromatographic columns, which make it possible to analyze the gas phase for the content of carbon dioxide and oxygen.

Oil and water are loaded into the autoclave, sealed, filled with oxygen-containing gas (air) to the required pressure, and the autoclave is checked for leaks. Then, with stirring, the reaction mass is heated to the reaction temperature and maintained for the required time. The initial conditions and experimental results are shown in Table 2.

In experiments 1 and 2 simulate the process of formation of carbon dioxide by a known method. Air is used as an oxygen-containing gas. The yield of carbon dioxide to absorbed oxygen increases with increasing oxidation depth (the number of moles of absorbed oxygen per 1 liter of oil) and amounts to 26.4 - 31.8% at oxidation depths of 2.52-5.03 mol / l.

Thus, despite the considerable depth of oil oxidation and the high temperature of the process (parameters conducive to an increase in the yield of carbon dioxide), the efficiency of the transformation of oxygen into carbon dioxide is not great.

Example 2

Oil is loaded into the autoclave, water and the experiment is carried out according to the procedure described in Example 1. After 5 hours of oxidation (which is sufficient for almost complete absorption of oxygen from the air), 50 ml of sodium bicarbonate solution with a concentration of 20 g / l is pumped into the autoclave with a high pressure pump ( experiment 3 in Table 2). The injection rate of 5 ml / min, the injection time of 10 minutes. Then the reaction mass is thermostated with stirring for 2 hours 50 minutes.

The data of Table 2 show that in experiment 3, the carbon dioxide output to the absorbed oxygen is 1.36 times higher than in the known method (experiment 1). Determination of the pH of the aqueous phase of the oxidate showed that it is 4.5 (acidic medium). In experiment 3, there was a complete conversion of sodium bicarbonate to carbon dioxide and salts of organic acids. Thus, even the incomplete conversion of the acid components of oil oxidate can significantly increase the yield of carbon dioxide and, as a consequence, its content in the gas phase after the completion of oxidation.

Example 3

Oil is loaded into the autoclave, water and the experiment is carried out according to the procedure described in Example 1. After 5 hours of oxidation (which is sufficient for almost complete absorption of oxygen from the air), 50 ml of sodium bicarbonate solution with a concentration of 80 g / l is pumped into the autoclave with a high pressure pump ( experiment 4 in Table 2). The injection rate of 5 ml / min, the injection time of 10 minutes. Then the reaction mass is thermostated with stirring for 2 hours 50 minutes.

The data of Table 2 show that in experiment 4, the yield of carbon dioxide to absorbed oxygen is 1.66 times higher than in the known method (experiment 2).

Determination of the pH of the aqueous phase of the oxidate showed that it is equal to 7 (neutral medium). In experiment 4, there was a complete conversion of organic acids of oil oxidate to carbon dioxide and sodium salts of carboxylic acids. Thus, the complete conversion of the acidic components of oil oxidate can significantly increase the yield of carbon dioxide and, as a consequence, its concentration in the gas phase after oxidation is complete.

table 2 Initial conditions and results of oil oxidation experiments Temperature ° C Experience number The initial load in the autoclave, ml Volume of gas phase, ml Initial pressure *, MPa Holding time, hour The conversion of oxygen,% Depth of oxidation, mol / l The concentration of sodium bicarbo nata, g / l The volume of sodium bicarbonate solution, ml The output of CO ₂ absorbed oxygen,% oil water before starting to pump sodium bicarbonate solution after starting the injection of the bicarbonate solution 200 one fifty one hundred 830 2.0 5.5 0 one hundred 2,52 - - 26,4 200 2 25.1 125 830 2.0 7 0 99.8 5.03 - - 31.8 200 3 50.1 one hundred 830 2.0 5 3 99.9 2,52 twenty fifty 35.9 200 four 25.1 125 830 2.0 5 3 one hundred 5.03 80 fifty 59.6

Example 4

Determination of oil-displacing efficiency of the gas mixture formed as a result of in-situ oxidation of oil by a known method, is carried out using a filtration unit. As an object of research, samples of Jurassic strata are used.

The study tested the oil-displacing ability of a mixture of CO ₂ and BFLH, the composition of which was modeled on the basis of ideas about the DVT mechanism carried out by a known method (Table 3).

Table 3 The composition of the model gas displacing agent The way to implement DVT Volume fraction of components,% Nitrogen CO ₂ C ₃ H ₈ C ₄ H ₁₀ C ₅ H ₁₂ Famous fifty 25 5 10 10 Proposed 8.5 41.5 5 10 10

To reproduce the real geological and physical conditions of the reservoir and the processes occurring during the injection of water and oil oxidation products, the following were observed in the filtration experiment in experiments:

1. a linear model of the reservoir is represented by samples of sandstone in productive formations. The permeability of the model for kerosene with bound water of 0.01 μm ² .

2. in the sandstone samples composing the reservoir model, create bound water in an amount of 25-29%, which corresponds to the values of this parameter in the reservoir;

3. in the experiments they use a recombined oil model, which in its physicochemical properties does not differ from reservoir oil (Table 4);

4. as displacing agents, water from the reservoir pressure maintenance system is used (ρ = 0.979 g / cm ³ , μ = 0.365 MPa · s at 90 ° C) and a model gas mixture (Table 3);

5. during the experiment, the thermobaric conditions of the deposit are observed (temperature 90 ° C, pressure 26 MPa).

The preparation of the model for the experiments is carried out according to generally accepted methods. The parameters of the linear reservoir model used in the experiment are presented in Table 5 (experiment 1).

A recombined oil sample is prepared from anhydrous oil taken from the field by dissolving the corresponding individual hydrocarbon gas components therein.

Table 4 Physical properties of reservoir oil and recombined oil samples Options Units measuring Reservoir oil, reservoir Yu ₁ °, measuring range Recombined Oil Model Reservoir pressure MPa 26 26 Formation temperature ° C 90 90 Saturation pressure MPa 3.8-7.6 5.8 Density at reservoir pressure (R _pl. ) g / cm ³ 0.743-0.786 0.778 Viscosity at R _pl. MPa · s 0.63-1.11 1,0 Volumetric coefficient of R _pl. grandfather. 1,113-1,155 1,114 Gas content m / t 48.7 43.5 Table 5 Initial parameters of linear reservoir models Filtration Experience Number) Number of samples Length cm Diameter cm Porosity,% Kerosene permeability, μm ² Bound water,% one 22 88.7 2.94 17.0 0.01 27.45 2 22 88.7 2.94 17.0 0.01 27.15

When setting experiment 1, technological operations are carried out in the following sequence:

1. filter water through the reservoir model to 100% water cut;

2. the rim of the model gas mixture is pumped into the reservoir model by a known method of DVT implementation;

3. filter water through the model to 100% of the water cut of the output. The results of the filtration experiment with the simulation of a known method are shown in Table 6.

The gas mixture formed as a result of the implementation of the known method,

allows to increase the oil displacement coefficient from 52% to 66%, i.e. by 14%.

Table 6 The results of filtration experiments Filtration Experience Number Uploaded Agent Injection volume in pore volumes of the reservoir model The coefficient of oil displacement,% The growth rate of oil displacement,% one Water 0.62 52 - The gas mixture according to a known method 0.31 52 0 Water 1.32 66 fourteen 2 Water 0.64 51 - The gas mixture according to the proposed experience 0.30 81 0 Sodium bicarbonate solution with a concentration of 20 g / l 0.10 52 one Water 1.21 82 31

Example 5

The determination of oil-displacing efficiency of a gas mixture formed as a result of in-situ oxidation of oil by the proposed method is carried out using a filtration unit.

The study tested the oil-displacing ability of a mixture of CO ₂ and BFLH, the composition of which is modeled on the basis of ideas about the DVT mechanism carried out by the proposed method (Table 3).

In experiment 2, the same reservoir model is used as in experiment 1 (Example 4). Before reuse, the rock samples are extracted with a benzene mixture, washed with water and dried. Preparation of the reservoir model for experiment 2 is carried out in the same way as in experiment 1. The properties of the model are completely restored (Table 3).

When setting experiment 2, technological operations are carried out in the following sequence:

1. filter water through the reservoir model to 100% water cut;

2. the rim of the model gas mixture is pumped into the reservoir model according to the proposed method for the implementation of DVT;

3. sodium bicarbonate solution,

4. filter through the model water up to 100% water cut of the output.

The results of the filtration experiment with the simulation of a known method are shown in Table 6.

The gas mixture formed as a result of the implementation of the proposed method allows to increase the coefficient of oil displacement by 31%.

Thus, the oil-displacing efficiency of the proposed method is more than 2 times higher than that of the known method.

Industrial applicability.

The proposed method of increasing oil recovery can be applied to increase the degree of oil displacement from fields located in the middle and late stages of development.

Example 6

At a section of an oil field, including 1 injection well and 3 production wells with an initial formation temperature of 118 ° C, air is pumped into the injection well at an average rate of 0.006 nm ³ / min for 60 days. Then, 1000 m ³ of sodium bicarbonate solution with a concentration of 50 g / l is pumped into the injection well, and then water is pumped. As a result of air injection in the reservoir, auto-displacement of oil occurs with a rise in temperature to 150-200 ° C. As a result of oil oxidation, a primary rim is formed containing N ₂ , CO ₂ and hydrocarbon vapors. The second rim, containing almost pure CO ₂ , is formed as a result of the interaction of the injected sodium bicarbonate NaHCO ₃ solution with oxidized oil located in the bottomhole formation zone.

As a result of these actions, oil recovery in the field increased by 3.4%.

Claims (2)

1. A method of increasing oil recovery of a field, including thermogas treatment of the formation by sequential injection of oxygen-containing gas and water into the formation, characterized in that when it is used in fields with formation temperature of 90-200 ° C, after the injection of oxygen-containing gas and before the injection of water, it is pumped into the formation alkali metal bicarbonate solution with a concentration of 20 - 80 g / l. 2. The method according to claim 1, characterized in that as the alkali metal bicarbonate, sodium or potassium bicarbonate or mixtures thereof are used.