RU2223398C1 - Process of recovery of viscous oil or bitumen from formation - Google Patents

Abstract

FIELD: oil production. SUBSTANCE: process is intended for development of fields of heavy crude and bitumen and can be employed in extraction of viscous oil and bitumen by thermal action on formation. Process of recovery of viscous oil and bitumen from formation includes heating of formation by injection of heat transfer agent and gas into it. In compliance with invention mixture of noncondensating gases formed in process of combustion of liquid fuel with following proportion of components, per cent by weight: nitrogen 15.2-19.0, carbon dioxide 4.8- 6.0, is utilized as gas. Content of gas in mixture with heat transfer agent amounts to 20-25 per cent by mass. Proportion of mixture and steam is calculated by empirical formula. EFFECT: intensified process of oil recovery, increased effectiveness of extraction of oil and bitumen thanks to combination of thermal and physico-chemical action, diminished content of water in oil. 1 tbl

Description

The invention relates to the field of the oil industry, in particular to methods for developing deposits of heavy oils and bitumen, and can be used in the production of viscous oils and bitumen by thermal action on the reservoir.

A known method of producing highly viscous oil, involving the injection into the well of steam or combustible gas at a pressure exceeding the mountain [see US Pat. US No. 3330353, CL 106-40, publ. 1967], while horizontal cracks are formed in the formation along which steam or gas moves and heats the oil contained in the pore space of the formation.

The disadvantage of this method is that when developing formations having a low reservoir pressure, after taking a certain volume of product, its inflow into the well stops, although the reservoir is still considered hot and the product is in a liquefied state.

There is also known a method of producing viscous oil or bitumen from a reservoir by heating by cyclic pumping heat carrier and gas into it [see US Pat. US No. 3782470, CL 166-303, publ. 1974].

The disadvantage of this method is the high energy costs associated with the injection of a large volume of coolant.

The closest in technical essence and the achieved result to the proposed is a method of producing viscous oil or bitumen from the reservoir [see a. from. USSR No. 834339, class E 21 B 43/24, publ. BI No. 20 for 1981], which includes heating the formation by pumping coolant and gas into it, while gas is pumped into the latter periodically before the next heating of the formation.

The advantage of this method is that an additional amount of heat is generated in the formation due to the low-temperature oxidation (NTO) of high-viscosity oil or bitumen with oxygen contained in the air, which contributes to an increase in the production rate of the well.

The disadvantage is that during NTO, destructive changes in the physicochemical properties of natural bitumen occur when it passes through the high-temperature zone, as well as the coking of the bottom-hole formation zone and the lower suspensions of tubing (tubing), which has a negative effect on efficiency displacement of viscous oil or bitumen as a whole and requires additional material costs.

The objective of the invention is to provide a method for efficiently displacing viscous oil or bitumen from a formation at relatively low energy costs.

The problem is achieved by the described method for the production of viscous oil or bitumen from the reservoir by pumping coolant and gas into it.

New is that as a gas use a mixture of non-condensable gases generated during the combustion of liquid fuel, with the following ratio of components, wt.%:

nitrogen - 15.2-19.0;

carbon dioxide - 4.8-6.0,

the gas content in the mixture is 20-25 wt.%, and the mixture of steam and gas is pumped out based on

Q _cm = 1.24 π h ³ ,

where Q _cm is the amount of injected gas, t;

1.24 - coefficient of accounting for the consumption of combined-cycle gas per 1 m ^{3 of the} bottom-hole zone established by experimental work;

h is the thickness of the working part of the reservoir, m, at a pressure of 0.2 - 0.8 MPa from the hydraulic fracturing pressure calculated by the formula

P _grp = P _g + δ;

where R _g - mountain pressure, MPa;

δ is the pressure associated with overcoming the forces of rock resistance to destruction, taken equal to from 1.5 to 3 MPa, depending on the density of the rocks.

The injection pressure should not exceed 0.8 hydraulic fracturing pressure in order to avoid its rupture.

The use of a mixture of non-condensable gases as gas additives in optimizing the ratio both in composition and in the content of the mixture with the coolant, as well as in the volume of injection of the gas-vapor mixture and injection pressure, makes it possible to increase the efficiency of the production of viscous oil or bitumen with the lowest heat loss and relatively low energy costs.

The method is carried out in the following sequence (combined with an example of a specific implementation).

A well was selected at the M. Karmalsky and Ashalchinsky viscous oil and bitumen deposits to test the proposed method for the production of viscous oils and bitumen, equipped in accordance with the existing development plan, and was additionally equipped with a research site, a manometer, a thermometer and a fluid sampling device.

The initial bitumen saturation of the formation was more than 50% of the pore volume, while the reservoir is characterized by the following parameters:

1) the depth of the bed, m, 60-150;

2) bitumen-saturated thickness, not less than, m, 3;

3) permeability, not less, microns ² , 0.52;

4) porosity, not less than,%, 18;

5) the dynamic viscosity of bitumen in reservoir conditions, Pa • s, 3-16;

6) pressure of injection of agents no more, MPa, 4;

7) the temperature of the coolant, ° C, 180-250.

When testing the proposed method for the production of viscous oil or bitumen used equipment used in the oil industry:

1) mobile steam and gas generators of the type UNPGG 6/6 with a productivity of 1-6 t / h with a gas temperature of 180-250 ° C;

2) portable compressors type SD 9/101;

3) water containers with a volume of 20-70 m ³ ;

4) containers for distillate with a volume of 10-70 m ³ ;

5) mobile steam generators of the type PPUA-1600/100, PGTU-3M, PPUA-1200/100;

6) logging stations of type SKT-1, SKT-2;

7) tank trucks.

Before the start of technological work, a set of well-known preparatory work was carried out, in particular:

- liquid samples were taken for analysis (density, viscosity, mechanical impurities, product temperature, chemical composition, group and fractional compositions);

- measured the fluid flow rate;

- beat off the static fluid level in the wells of the site;

- reduced the fluid level to the tubing shoe and removed the level recovery curve;

- created a circulation of hot water (t ≥ 70-80 ° C) in the injection well. Circulation was performed until pure water appeared;

- blew out water;

- after checking the circulation, the injectivity of the well was measured for the combined gas produced by the UNPGT-6/6 steam and gas generator.

- determined the interval of injectivity of the formation, using the station type SKT.

When steam was injected into the well, the bottom-hole zone of which is not rarified, at the initial stage, a cyclic effect was made on the formation with periodic injection measurement until it reached a value of 1-6 t / h. The injection was carried out at a maximum pressure not exceeding 0.8 R _fracturing according to the formula described above.

Laboratory studies found that when injecting a gas-vapor mixture, the content of the gas component should not exceed 20-25 wt.% (250 m ^{3 of} gas per 1 ton of steam). This is the optimal ratio at which the maximum displacement rate of bitumen is noted. A further increase in the content of the gas component does not lead to an increase in the displacement coefficient of bitumen.

At the end of the injection of the required volume of gas-vapor mixture, the well was stopped for exposure to thermocapillary impregnation. The aging process with periodic temperature control was continued until the reservoir temperature dropped to 70-80 ° C.

Then the well was poured into the spout and production was taken into the prefabricated reservoir until the supply ceased. Samples were sent at least once a week for analysis (water cut, density, viscosity, mechanical impurities, product temperature, chemical composition, group and fractional composition).

In the process of fluid sampling twice a month, formation coverage was determined by thickness (inflow profile).

To control the zone of heating and drainage of cyclically operating wells once a month, the electrical potentials of the site were taken.

If there is a hydrodynamic connection between neighboring wells, a thermocouple was installed in the producing well to control the temperature at the bottom of the well, then they switched to areal injection of steam and gas.

Experience has shown that introducing only steam into the formation as a viscosity reducer for bitumen due to an increase in temperature in the formation and creating elastic energy in the formation is not enough. Elastic energy is quickly lost, and the temperature quickly drops to its original value. When combined with gas, the non-condensing gas component is introduced in addition to thermal energy, which increases the elastic energy of the formation and, as a result, ensures intensive movement of fluid to the bottom of the wells.

The results of experimental studies of oil displacement by a gas-vapor mixture of steam with CO ₂ and N ₂ revealed a significant difference in the dynamics of gas-gas displacement from the dynamics of displacement with pure steam. In the temperature distribution along the length of the model, in contrast to steam, a gas temperature is characterized by a noticeable increase in temperature when moving along the model, which is associated with the presence of non-condensing gases and heat loss. In the case of oil displacement by pure steam with nitrogen and carbon dioxide, the displacement coefficient is significantly higher compared to the displacement of pure steam. When oil is displaced by a gas-vapor mixture, to achieve the same value of the displacement coefficient, less steam is required than in the process of displacement by pure steam, that is, lower vapor-oil and water-oil ratios are typical for combined-cycle gas.

Use as a gas component of air is unacceptable. The interaction of air with the gases of the reservoir gives an explosive mixture.

At the same time as the coolant was injected into the injection well, the level of fluid in the surrounding wells was monitored. Once a day, the pressure at the mouth of the producing wells of the site (element) was monitored. When the pressure at the wellhead of more than 0.1 MPa was reached, the well was launched into the spout.

The temperature of production of producing wells was monitored daily according to the testimony of a portable thermometer at the wellhead. With an increase in the temperature of the product above 80 ° C and in the case of breakthrough of the gas to the bottom of the producing wells, the selection of products was stopped.

The injection of gas was stopped after a constant temperature was established in the producing well. The injection well was closed for exposure to thermocapillary impregnation until the temperature in the bottomhole zone drops to 70-80 ° C.

After thermocapillary impregnation, injection and production wells were put into operation. In the event of an inflow, wells were operated in the following mode:

- the producing well worked in the selection mode;

- the injection well worked in a cyclic mode:

“injection” until the temperature at the bottom of the producing well reaches 80 ° C - “exposure”; selection.

The cycle was repeated until the feed was cut off in the producing well.

In the event of a repeated gas breakthrough, the selection of production and the injection of steam and gas were stopped, the wells were installed for thermocapillary impregnation, and a decision was made about the possibility of transferring these wells to the opposite category.

If there is no hydrodynamic connection with the surrounding wells of the section, they switched to cyclic exposure to steam and gas in the producing wells, repeating the work starting from the injection of gas into the injection well. The cycles were repeated until hydrodynamic coupling was achieved.

In case of uneven advancement of the heating front, the selection from the nearest producing wells was stopped and measures were taken to level the front.

The results obtained in laboratory studies and tested in the field are shown in the table.

Note: BOD - blocking of pore channels.

The table shows that when injecting a vapor-gas mixture containing 20-25 wt.% A mixture of non-condensable gases, a maximum bitumen recovery of 38-44 wt.% Is achieved. The specified recovery factor is achieved on rocks having a permeability of 1.1-2 μm ² . At lower rock permeabilities, pore channels become blocked.

The studies revealed the efficiency of pumping a mixture of steam with non-condensable gases, which is associated with:

- with the ability to control the displacement process by the hot water zone;

- with the dependence of the temperature of vapor condensation on the content of the inert component of the gas;

- with gas and water repression;

- with mass transfer between the gas and liquid phases.

The laboratory and field studies have established the optimal composition of the gas component, the optimal ratio of the gas mixture, the optimal gas consumption per 1 m ^{3 of the} bottomhole zone. The permeability interval of the reservoir is given at which the maximum recovery occurs.

Field tests of steam-gas technology using a mixture of non-condensable gases generated during the combustion of liquid fuels at M. Karmalsky and Ashalchinsky deposits of natural bitumen showed that the average bitumen production rate for a number of wells after its application in comparison with conventional steam treatment increased by four times, water cut decreased by half.

Claims (1)

A method of producing viscous oil or bitumen from a formation by heating by pumping coolant and gas into it, characterized in that the gas used is a mixture of non-condensable gases generated during the combustion of liquid fuel, in the following ratio of components, wt.%: Nitrogen 15.2 - 19.0 Carbon Dioxide 4.8 - 6.0 the gas content is 20-25 wt.%, and the mixture of steam and gas is pumped out based on Qcm = 1.24 π h3, where Qcm - the amount of injected gas, t; 1.24 - the coefficient of accounting for combined-cycle gas per 1 m ^{3 of the} bottom-hole zone established by experimental work; h is the thickness of the working part of the reservoir, m, at a pressure of 0.2-0.8 MPa from the hydraulic fracturing pressure.