RU2247830C2 - Method for extraction of deposits of high-viscous oil and bitumen - Google Patents

Abstract

FIELD: oil extractive industry.

SUBSTANCE: method includes cyclic differently-directed forcing of air as oxidizer. This is achieved by changing oxidizer forcing pressure and its volume, changing position of air forcing points, extraction of high-viscous oil or bitumen. Appearance of sign-alternating pressures between beds of different saturation provides for acceleration of capillary counter-flow saturation with water of zones with oil or bitumen, forcing gases into portions with oil or bitumen along small porous channels and transfer of oil or bitumen from heated areas along large porous channels. Change of direction of flows of gas of oil or bitumen between wells strengthens process of increase of area of effect of bed by bed inside burning. In such a way, use of stagnant areas is increased and bitumen extraction coefficient is increased.

EFFECT: higher efficiency.

1 ex, 1 tbl, 2 dwg

Description

The invention relates to the field of the oil industry, in particular to methods for developing deposits of high viscosity oil (BBH) or bitumen by in-situ combustion, and can be used to regulate the process of in-situ combustion (SH) using unsteady modes of pumping air as an oxidizer during the displacement of BBH or bitumen from permeable layers.

There is a method of developing deposits of high viscosity oils by in-situ combustion, including the injection of air into the injection and the selection of products through production wells. [Cm. US Pat. US No. 3179167, CL 166-11, published. - 1965].

The method provides for continuous air injection until the high-temperature zone approaches the production well, and then a transition to cyclic air injection.

The disadvantage of this method is the low coefficient of coverage of combustion and the difficulty of controlling the movement of the combustion front during repeated cycles. This is explained by the fact that the combustion front, moving along more permeable sections to the producing well, covers the reservoir only of small thickness, since during repeated cycles the combustion front will move mainly along the same interlayers as before. This is explained by the fact that after bringing the combustion front or high-temperature zone to the production well, the heterogeneity of the formation only increases, since in more permeable layers or cracks, high-viscosity oil is replaced by a more mobile agent (air or water).

There is also known a method of developing high viscosity oil or bitumen [see RZH "Mining", consolidated volume, 1969, No. 6, ind. 6G253P].

The method includes cyclic injection through the injection wells of air with a constant flow rate and the selection of reservoir products through production wells. During periods of stopping the injection of air into the formation through injection wells, water is pumped to lower the temperature of the formation below the temperature of oil cracking. After water injection, oil is extracted through production wells until the reservoir temperature remains above the ignition temperature of the reservoir oil with the subsequent resumption of oxidant injection.

The main disadvantage of this method is the low coverage of the formation by combustion and, accordingly, the low oil recovery coefficient due to the fact that this method provides a constant rate of air injection without taking into account the temperature situation in the formation and the rate of burning of fuel over time.

When large volumes of air are pumped in, an excess of oxygen is created at the beginning of the cycle (during this period, the fuel burning rate is slowed down due to a decrease in temperature), which, breaking through the combustion front to production wells, forms an explosive mixture with hydrocarbon gases. This leads to the forced termination of the reservoir development process.

Thus, when the air is injected at a constant speed, the combustion process is unregulated, which ultimately reduces the main development indicator - oil recovery.

The closest in technical essence and the achieved result to the proposed is a method of developing deposits of high viscosity oil or bitumen [see US Pat. RU No. 1129986 dated 07.15.83, cl. E 21 B 43/24], which consists in the injection of air through injection wells and the selection of formation products through production wells, the air injection in each cycle is carried out at an increasing rate and, after reaching the maximum possible air flow rate, it is pumped at a constant rate, and the daily air flow rate during periods increasing the rate of injection is determined from the following ratio:

where q _t is the daily air flow at time t (nm ³ / day);

Δt is the duration of the period of increasing the daily air flow in the cycle (days);

t - current time (days);

q _min - the initial air flow in the cycle (nm ³ / day.);

q _max - the maximum possible air flow (nm ³ / day.);

Cyclic injection of the oxidizing agent in an increasing mode contributes to an increase in the coverage of the formation by combustion.

The disadvantage of this method is the limited use, since when the geological and physical characteristics of the developed high-pressure formations change, its effectiveness drops sharply due to the inability to control the air injection process. The technical task of the proposed method for the development of deposits of highly viscous oil or bitumen is to increase the efficiency of developing heterogeneous deposits by regulating the in-situ combustion process using unsteady modes of air injection as an oxidizing agent and a combination of thermal and hydrodynamic effects on the formation.

The problem is solved by the described method of developing VVN or bitumen by creating an in-situ combustion zone, including cyclic air injection with a change in the rate of its injection through injection wells and the selection of VVN or bitumen through production wells.

New is that the optimal frequency of air injection cycles is determined by the formula

t _{1/2 c} = L ² / 2χ,

where t _{1/2 C} - the duration of the half-cycle of injection of the oxidizing agent into the reservoir, days .;

L is the characteristic length of the reservoir, m;

χ is the average piezoelectricity of the reservoir,

χ = k / μ c m,

Where

μ is the viscosity of BBH or bitumen, Pa · s;

K is the permeability of the formation, μm ² ;

m — formation porosity, fractions of a unit;

with - the coefficient of elastic capacity of the reservoir, 1 / MPa, (2 ÷ 5) · 10 ^-4 .

In this case, the amplitude of fluctuations in the discharge air flow rate is defined as the ratio of the excess or decrease in the level of air injection over the average discharge volume during cyclic in-situ combustion to the average level of air injection during its stationary injection according to the formula:

B = (Q _i3 -Q ₀₃ ) / Q ₀₃ ,

Where

B is the amplitude of the fluctuations in the discharge air flow rate.

Q ₁₃ - the maximum or minimum level of air injection depending on the phase of the cycle, with cyclic in-situ combustion (Q _{13 min} = 0), nm ³ / day .;

Q ₀₃ - the average level of stationary air injection (Q ₀₃ = Q _13/2 ), nm ³ / day .;

_i is the cycle number (i = 1, 2),

moreover, the beginning of the cyclic air injection is determined by the time the combustion gas breaks into the production well during stationary injection of air through the interlayer with higher permeability, the location of the air injection points and the extraction of explosives or bitumen are periodically changed, and the manifestation of the effect of cyclic exposure is determined as additional production of explosives or bitumen according to the stable integral dependences of the volume of recovered explosives or bitumen and injected air of the form:

Q (t) = f [Q _air (t)],

Where

Q (t) is the accumulated volume of mined explosives or bitumen from the site by a given tracking time, t;

Q _air (t) is the accumulated volume of injected air at a given moment, m ³ .

The proposed method for the development of deposits of high viscosity oil or bitumen during in-situ combustion is based on a combination of thermal and hydrodynamic effects on the reservoir. The hydrodynamic effect consists in periodically changing the volume of air injection and the selection of liquid. The thermal effect is obtained as a result of air supply as an oxidizing agent.

In the unsteady mode of air injection between zones of the formation with different permeability and bitumen saturation, alternating pressure gradients are created, under the influence of which the process of capillary impregnation increases.

In connection with the cyclic change in the volumes of air injection and the extraction of explosives or bitumen in the development element, periods of increase and decrease in reservoir pressure occur, under the influence of which the process of capillary impregnation increases.

During periods of increasing injection volumes, the growth rate of pressure in gas-saturated highly permeable and adjacent bitumen-saturated zones will differ due to the difference in their conductivity. In this case, positive pressure gradients arise, under the influence of which the flow of explosives or bitumen passes from bitumen-saturated zones to gas-saturated ones.

With a subsequent increase in pressure, the BBH or bitumen will be forced out to the extraction zones. Thus the cycle repeats. From cycle to cycle, coverage of stagnant zones will increase and bitumen recovery coefficient will increase.

Repeated saturation jumps arising as a result of uneven displacement of bitumen by gases from heterogeneous formations create an nonequilibrium state of capillary forces at the contact of zones with different saturations. The occurrence of alternating pressures between layers of different saturation promotes the acceleration of capillary countercurrent impregnation of bitumen-saturated zones with water, the introduction of gases into bitumen-saturated areas through small pore channels and the flow of explosives or bitumen from heated zones through large pore channels. A change in the direction of the VVN or bitumen gas flows between the wells enhances the process of increasing the coverage of the formation by in-situ combustion.

The process of changing the direction of filtration flows takes quite a long time. Depending on the permeability of the layers, the process of stabilization of flows can last from several tens of days to several months. Therefore, the manifestation of the effect of cyclic exposure occurs with some delay. The effect in the form of additional production is determined by the integral indicators of the volume of recovered explosives or bitumen and the injected air - oxidizer.

The in situ combustion mechanism in the formation determines a direct relationship between the volumes of air injection and the production of explosives or bitumen. Differential dependencies between them due to the delay in the effect of non-stationary air injection are unsuitable. Therefore, it is necessary to use stable integral relationships between injection volumes and the extraction of explosives or bitumen.

The combination of distinctive features allows to increase the efficiency of the development of heterogeneous deposits due to the regulation of the SH process with the help of non-stationary modes of oxidizer injection and a combination of thermal and hydrodynamic effects on the formation.

From the available sources of patent and scientific and technical literature, we do not know the claimed combination of distinctive features. Therefore, the proposed method meets the criteria of the invention "inventive step".

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

A number of wells were selected at the Mordovo-Karmal bitumen deposit for testing the proposed method for developing deposits. Wells were equipped in accordance with the existing construction project, and were additionally equipped with a research site, a manometer, a thermometer and a device for sampling bitumen.

The initial bitumen saturation of the formation was at least 40% of the pore volume, while the reservoir is characterized by the following parameters:

1) the depth of the bed, m - up to 120;

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

3) the permeability of the formation, μm ² - not less than 0.5;

4) porosity, fraction of units - not less than 0.18;

5) the dynamic viscosity of bitumen in reservoir conditions, Pa · s - 3-10;

6) the coefficient of elastic capacity of the formation, depending on the saturation of the formation with bitumen and gases, and characterizes the degree of compressibility of the formation per unit pressure, which varies in the range - (2 ÷ 5) · 10 ^-4 , 1 / MPa, to find the optimal values from the point of view of achieving set technical task.

During the operation of the field by the proposed method, the pressure of the coolant injection into the formation was not more than 4 MPa, the coolant temperature was not higher than 250 ° C.

When testing the proposed method for the development of deposits of VVN and natural bitumen used equipment used in the oil industry:

- stationary compressors type OVG-75-70 U;

- mobile logging stations of type SKT-1 and SKT-2;

The control of the discharge pressure was carried out according to the readings of pressure gauges installed before and after the fitting on the discharge lines.

Accounting for injection volumes was carried out by calculation, depending on air humidity and injection pressure per unit volume of the reservoir (140-160 nm ³ / m ³ ).

When developing bitumen-saturated formations or formations with VVN by the SH method, the technology provides stable formation heating, the optimum temperature at the combustion front is not higher than the ignition temperature of the formation (not higher than 250 ° C).

Before starting work, the wellhead equipment was inspected for leaks, pressure gauges and thermometers were installed.

Control measurements of flow rate, formation temperature, static level were taken, gas and liquid samples from reacting wells were taken.

The purpose of the air injection is to maintain the focus of combustion in the bituminous formation.

The essence of changing the air injection mode is to regulate the combustion process of bitumen in the formation and its movement to the producing well with a more complete coverage of the developed section of the formation with the thermal effect.

The estimated air volume was determined based on the conditions of a particular well (element). The maximum rate of injection into one well is 30-40 thousand nm ³ / day. (actual).

The well was launched for the injection of air with a modified volume.

The amplitude of the fluctuations in the flow rate of the injected air is defined as the ratio of the excess or decrease in the level of air injection over the average injection volume during cyclic in-situ combustion to the average level of air injection during its stationary injection according to the formula

B = (Q _i3 -Q ₀₃ ) / Q ₀₃ ,

where In - the amplitude of the fluctuations in the flow rate of injected air;

Q ₁₃ - the maximum (or minimum) level of injection (depending on the phase of the cycle) with cyclic SH, nm ³ / day .;

Q ₀₃ - the average level of stationary air injection, nm ³ / day .;

(Q _{13 min} = 0; Q ₁₃ = 2Q ₀₃ ); i is the number of the cycle (i = 1, 2).

Provided that it is necessary to keep the average volume of cyclic air injection equal to the volume during stationary injection "B", it cannot be more than 1. This means that in the half-period of increasing the discharge pressure, the volume of air injection should double and in the half-period of decreasing pressure should be reduced to 0 shutdown of injection wells. We measured the temperature of the bottom-hole zone of the injection well. In the case of application of the method on the element, the volume was reduced or the air injection into injection wells was stopped for 10-30 days, continuing the selection of bitumen from production wells in the previous mode. The optimal cycle frequency obtained from hydrodynamic calculations is determined by the formula

t _{1/2 c} = L ² / 2χ,

Where

t _{1/2 c} - the duration of the half-cycle of injection of the oxidizing agent into the reservoir, days .;

L is the characteristic length of the reservoir, m;

χ is the average piezoelectricity of the reservoir,

χ = k / μ s m,

Where

μ is the viscosity of bitumen, Pa · s;

K is the permeability of the formation, μm ² ;

m — formation porosity, fractions of a unit;

C is the coefficient of elastic capacity of the reservoir, 1 / MPa.

For the Mordovian-Karmal deposit t _{1/2 c} = 30 days. On the third day from the start of injection, then periodically - once a week, measurements of formation temperature, levels were carried out, gas and bitumen samples were taken from the reacting wells.

Restored air injection with a volume increased to two times in the injection well (with a daily flow rate of 30-40 thousand nm ³ / day) for 10-20 days, while stopping the selection of bitumen from producing wells for 5-10 days. (Due to the delay in the time of manifestation of the effect of the cyclic effect according to observations, the time of termination of selection changed approximately twice as appropriate).

If the bitumen production rates of the wells did not exceed the production rates before air injection, then the next cycle of air injection was carried out, starting from the start of the well for the injection of air with a changed volume. If the flow rate of the reacting wells was exceeded after air injection, the formation continued to operate until the flow of bitumen into the reacting wells ceased.

In the absence of the effect of air injection on the reservoir, another well was selected and prepared for air injection.

Air was injected into another well in the injection mode into the main well.

A change in the injection site and a change in the volume or pressure of the injection in order to change the filtration flows were carried out on several elements simultaneously.

Evaluation of the effectiveness of the proposed method was made by comparing the flow rate and watering of the reacting wells before and after cycling or by constructing the displacement characteristics (Fig.1-2).

Figure 1 shows the accumulated bitumen production of the prototype. Figure 2 shows the accumulated production of bitumen by the proposed method for the development of deposits of VVN or bitumen in the form of a hatched area, located above the line of straight-line extrapolation of the relationship between Q _b (t) and Q _air. (t).

Wells of elements were selected for cyclic air injection, at which the current formation output was 10-30%.

The growth rates of bitumen production for the period under review for each element of the field where cyclic air injection was carried out are summarized in the table.

Table Item no. The increase in production for the period under review, thousand tons thirteen 0,03 306 0.15 303 0.2 320 0.33 342 0.67 345 0,03 362 0.19 381 0,07 401 0.004 404 0.13 Total 1,804

An analysis of the development of elements showed that the efficiency of non-stationary air injection at the Mordovo-Karmal deposit of natural bitumen in the form of additional production was observed to varying degrees for all considered elements, which ranges from 0.03 to 0.67 thousand tons, and the cumulative production of bitumen according to the proposed method as a whole is 144 thousand tons against 142.2 thousand tons of the prototype.

The technical and economic efficiency of the proposed method consists of increasing the efficiency of developing heterogeneous deposits by regulating the in-situ combustion process using non-stationary modes of air injection as an oxidizing agent in combination with thermal and hydrodynamic effects on the formation.

In total, additional production for the entire period of pilot development amounted to 1.8 thousand tons.

Claims (1)

A method for developing deposits of highly viscous oil or bitumen by creating an in-situ burning zone, including cyclic injection of air as an oxidizing agent with a change in its rate of injection through injection wells and selection of highly viscous oil (BBH) or bitumen through production wells, characterized in that the optimal frequency of oxidant injection cycles is determined according to the formula: t _{1 / 2c} = L ² / 2χ, where t _{1 / 2c} - the duration of the half-cycle of air injection into the reservoir, days .; L is the characteristic length of the reservoir, m; χ is the average piezoelectricity of the reservoir, χ = k / μсm, where μ is the viscosity of BBH or bitumen, Pa · s; K is the permeability of the formation, μm ² ; m — formation porosity, fractions of a unit; C is the coefficient of elastic capacity of the reservoir, 1 / MPa, the amplitude of the fluctuations in the flow rate of the injected air is defined as the ratio of the excess or decrease in the level of air injection over the average discharge volume during cyclic in-situ combustion to the average level of air injection during its stationary injection according to the formula B = (Q _i3 -Q ₀₃ ) / Q ₀₃ , where B is the amplitude of the fluctuations in the discharge air flow rate; Q _i3 - the maximum or minimum level of air injection depending on the phase of the cycle during cyclic in-situ combustion (Q _i3min = 0), nm ³ / day .; Q ₀₃ - the average level of stationary air injection (Q ₀₃ = Q _i3 / 2), nm ³ / day .; i is the cycle number (i = 1,2), moreover, the beginning of the cyclic air injection is determined by the time the combustion gas breaks into the production well during stationary injection of the oxidizing agent through the interlayer with higher permeability, the location of the air injection points and the extraction of explosive or bitumen are periodically changed, and the manifestation of the effect of the cyclic effect is determined as additional production from stable integral dependences of the volume of recovered explosives or bitumen and injected air of the form: Q (t) = f [Q _air (t)], where Q (t) is the accumulated volume of mined explosives or bitumen from the site by the given tracking time, t; Q _air (t) is the accumulated volume of injected air at a given moment, m ³ .

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