RU2615198C1 - Method of exploitation of subsurface storage of natural gas - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention is targeted at the exploitation of the subsurface storages of gas (SSG). In the SSG, at which in the crestal area of the collector layer the producing wells are constructed, the deep disposal wells in the provinces of the collector layer and the control wells in the intermediate area between the producing and the deep disposal wells, produce the cycling pumping of the natural gas to the storage with creating of its buffer and active volumes and the separation of the natural gas. During the process of the SSG exploitation, the carbon dioxide is pumped to its lower section in the overcritical aggregative state and the buffer volume of the natural gas is replaced by it.

EFFECT: improving the quality of the stored natural gas at the expense of the lowering the risk of creation of the rich zones of combination the natural gas and the carbon dioxide, effective exploitation of the subsurface storages of gas at the expense of the replacing the part of the buffer volume of the stored natural gas into the carbon dioxide based on the reasoned choice of the aggregative state of the carbon dioxide.

12 dwg

Description

The invention relates to the field of the gas industry and is intended for the operation of underground gas storages (UGS).

A known method of creating and operating an underground storage of natural gas in porous and permeable reservoirs of mountain structures saturated with water, depleted gas and gas condensate fields, including drilling or using existing production wells, cyclic injection and selection of gas from underground gas storage with the formation of buffer and active storage volumes [ cm. A.I. Shirkovsky. Development and operation of gas and gas condensate fields. M .: Nedra, 1987, p. 271-302].

The disadvantage of this method is that in the process of natural gas extraction there remains a certain volume of it, depending on geological, technological and other reasons, which is called the buffer volume. Buffer gas is necessary to maintain a certain pressure in the underground gas storage facility at the end of extraction; this gas must be in the underground gas storage facility during its operation. The buffer volume of gas can reach half or more of the total gas volume in the UGS facility after the injection cycle, which is economically disadvantageous.

The closest in technical essence to the claimed method (prototype) is a method of operating an underground natural gas storage, including the construction of production wells with opening of the storage manifolds, cyclic injection into the natural gas storage with the creation of its buffer and active volumes, and the selection of the active volume of natural gas, during operation of the underground gas storage, carbon dioxide (CO ₂ ) is pumped into its lower part and natural gas is replaced in the buffer volume, and the selection of active its volume is carried out until the appearance of traces of carbon dioxide in the production of wells [see Patent for invention RU No. 2532278/11 dated 12.24.2012].

The main disadvantage of this method is that it is proposed to replace the buffer volume of stored natural gas CO ₂ without taking into account its state of aggregation. This will lead to the risks of an early CO ₂ breakthrough to the faces of production wells, as well as to the formation of extensive mixing zones of natural and carbon dioxide.

The objective of the proposed method is the creation of such a method of operating an underground storage of natural gas, which would reduce the risks of early breakthrough of CO ₂ to the faces of production wells, as well as the risks of the formation of extensive mixing zones of natural and carbon dioxide.

The technical result of the proposed method is to improve the quality of stored natural gas by reducing the risk of early breakthrough of CO ₂ to the faces of production wells, as well as the risk of the formation of extensive mixing zones of natural and carbon dioxide. In addition, the proposed method allows for more efficient use of UGS facilities by replacing part of the buffer volume of stored natural gas with CO ₂ based on a reasonable choice of the state of aggregation of CO ₂ .

The specified technical result is achieved due to the fact that in the method of operating the underground natural gas storage, including the construction of production wells in the domed part of the reservoir reservoir, cyclic injection into the natural gas storage with the creation of a buffer and its active volumes and selection of the active volume of natural gas, during operation of the underground gas storage, carbon dioxide (CO ₂ ) is injected and natural gas is replaced in a buffer volume, and a reservoir with thermobaric steam is selected meters: reservoir pressure Р _pl ≥73.8 bar and reservoir temperature Т _pl ≥31 ° С, sealed CO ₂ cover and injection wells are being constructed at the periphery of the reservoir and control wells in the intermediate zone between production and injection wells the cycle through the injection wells carries out the selection of natural gas from the zone of the buffer volume of gas in the case of a water-pressure regime until formation water appears in the production of wells, in the case of a gas regime until a predetermined minimum reservoir pressure, then through the injection wells is injected CO ₂ in the supercritical state of aggregation until the initial reservoir pressure, then in the first operating cycle of natural gas extraction is carried out through the production wells, wherein the monitor appearance of the supercritical CO ₂ in the control wells are natural gas extraction to complete the selection of the active volume of the natural gas, either before the supercritical CO ₂ in the control wells is then pumped natural g h through production wells to restore the active volume of natural gas then kept neutral during the second work cycle is carried download supercritical CO ₂ through the injection wells to the maximum formation pressure, or until the supercritical CO ₂ in the control wells, after which the natural gas extraction is carried through production wells, while supervising the appearance of supercritical СО ₂ in the control wells, they stop the selection when supercritical is detected ical CO ₂ in control wells, whereupon supercritical CO _{2 is} completely discontinued into the reservoir if supercritical CO ₂ is detected in control wells, to compensate for excess over the initial reservoir pressure, the extraction of active natural gas is increased, then the active volume of natural gas is injected into the third cycle when supercritical СО _{2 is} detected in control wells, the buffer volume of natural gas is replaced by supercritical СО ₂ , and the selection and injection of natural gas about gas perform in the amount of active volume.

The stated technical problem is solved due to the fact that during the operation of the underground gas storage, supercritical СО ₂ is injected into the reservoir, which has thermobaric parameters characteristic of the supercritical state of СО ₂ (Р _pl ≥73.8 bar, T _pl ≥31 ° С ), on the wings of the structure (the peripheral part) and replace them with natural gas in the buffer volume. The selection of the active volume of natural gas is carried out before detecting traces of supercritical CO ₂ in control wells.

In FIG. 1 shows a phase diagram of CO ₂ .

In FIG. Figure 2 shows a graph of the distribution of CO ₂ concentration over the reservoir for object X (with the horizontal position of the wings of the reservoir), where C is the concentration of CO ₂ , x is the distance traveled by the CO ₂ front from the moment of injection.

In FIG. Figure 3 shows a graph of the distribution of CO ₂ concentration over the formation for object Y (with horizontal arrangement of formation wings).

In FIG. Figure 4 shows a graph of the distribution of CO ₂ concentration over the formation for object X (with a slope of the formation wings of 15 degrees).

In FIG. Figure 5 shows a graph of the distribution of CO ₂ concentration over the formation for object Y (with a slope of the formation wings of 15 degrees).

In FIG. 6 presents a diagram of the operation of underground gas storage in a known manner [see Patent for invention RU No. 2532278/11 dated 12.24.2012].

In FIG. 7 presents a diagram of the operation of underground gas storage in a known manner during the injection of CO ₂ .

In FIG. 8-9 presents a diagram of the operation of the UGS facility according to the claimed method in the preparatory cycle.

In FIG. 10-11 presents the operation diagram of the UGS facility according to the claimed method in the first working cycle.

In FIG. 12 shows an arrangement of injection wells.

Consider the implementation of the claimed method.

In reservoir conditions, CO ₂ can be in various aggregate states depending on temperature and pressure: liquid, gaseous, and supercritical.

In the gaseous state, CO ₂ is a colorless gas with a sour taste and smell. It corresponds to a wide range of temperatures and pressures, not exceeding the boiling curve AB (Fig. 1). The density of gaseous CO ₂ under reservoir conditions will be slightly higher than the density of methane. Viscosity is of the order of 10 ^-5 Pa × s, diffusion coefficient is 10 ^-5 m ² / s.

At temperatures below 31 ° C and pressure limited by the boiling line AB (Fig. 1), CO ₂ is in a liquid state. It is a colorless, odorless liquid. Depending on thermobaric conditions, its density varies from 600 to 1200 kg / m ³ . The viscosity of the order of 10 ^-3 Pa × s, the diffusion coefficient of 10 ^-9 m ² / s.

At a pressure of 73.8 bar and a temperature of 31 ° C and above, CO ₂ is in a supercritical state. This means that there are no differences between the liquid and vapor phases. CO ₂ behaves like a gas-like compressible fluid, but at the same time it has a density close to the density of the liquid. With increasing temperature or pressure, the density of CO ₂ approaches in value to the density of the liquid, and its viscosity - to the viscosity of the gas. At reservoir temperature and pressure, corresponding to the region of supercritical state, the density varies from 600 kg / m ³ to 900 kg / m ³ . Viscosity is of the order of 10 ^-5 -10 ^-4 Pa × s, diffusion coefficient is 10 ^-8 m ² / s.

It follows from the above that for the replacement of part of the buffer volume of the stored natural gas to CO ₂ Least suitable liquid aggregate state CO _2, since in this case requires large volumes of liquid CO _2, as well as injection of liquid CO ₂ is lost useful gazoporovy amount that will lead to reduce trap capacity.

The diffusion coefficient is highest for gaseous, less for supercritical and smallest for liquid CO ₂ . Then the diffusion rate in descending order is gaseous, supercritical, liquid CO ₂ .

Based on the continuity equations for a gaseous mixture of two components, the injection of CO ₂ into the reservoir was simulated, followed by the replacement of part of the buffer volume of gas.

Filtration of a mixture of two gases in the one-dimensional case, taking into account gravity, is described by the following system of equations [see: Basniev KS, Dmitriev NM, Kanevskaya RD, Maksimov VM Underground hydromechanics. - M. - Izhevsk: Institute for Computer Research, 2006. - p. 328-337]:

Where

x - coordinate [m];

t is the time [s];

p = p (x, t) is the pressure in the reservoir [MPa];

c = c (x, t) is the concentration of CO ₂ gas in the formation, respectively (1-c) is the concentration of natural gas in the formation [CU];

ρ ₁ = ρ (p) is the density of CO ₂ [kg / m ³ ];

ρ ₂ = ρ (p) ^_ density of natural gas [kg / m ³ ];

μ ₁ = μ (p) ^_ viscosity CO ₂ [MPa × s];

μ ₂ = μ (p) ^_ viscosity of natural gas [MPa × s];

m is the porosity of the formation [CU];

k is the permeability coefficient of the formation [m ² ];

g is the acceleration of gravity [m / s ² ];

α is the angle of inclination of the formation to the horizontal [degrees].

The obtained problem is solved numerically by the finite-difference method. On each layer, there is first pressure, which is then used to find the concentration, after which the transition to the next layer is carried out.

An example implementation of the method

For example, we selected model underground gas storage facilities X (gaseous СО ₂ ) and Y (supercritical СО ₂ ) with the same temperatures and reservoir properties, but with different initial reservoir pressures characteristic of the gaseous and supercritical state of СО ₂ . The objects are reservoir deposits with the following main parameters. The initial reservoir temperature T _PL = 35 ° C, the permeability of the formation k = 150 mD, the porosity of the formation m = 0.25 CU for both layers. Some embodiments was simulated injection of CO ₂ underground storage sites X and Y horizontal (Figs. 2, 3) and inclined (Fig. 4, 5) located reservoir wings.

In FIG. 2 and 3 it is seen that the smear zone (mixing zone of CO ₂ and natural gas) of gaseous CO ₂ with a horizontal location of the reservoir is 42 meters, while supercritical CO ₂ is 29 meters. Thus, the mixing zone in the case of injection of the supercritical CO ₂ is less than in the case of gaseous CO _2, allowing a greater amount of substitute natural gas.

In FIG. 4 and 5 it is seen that the smear zone of gaseous CO ₂ is 92 meters, while supercritical CO ₂ is 62 meters. The inclined location of the formation wings directly affects the increase in the smear zone. Gaseous CO ₂ has a lower viscosity compared to supercritical CO ₂ , which leads to greater spreading inside the reservoir (traces of gaseous CO ₂ are 200 meters in contrast to supercritical CO ₂ ). At the same time, greater gravity acts on CO ₂ in a supercritical state than on gaseous CO ₂ , thereby enhancing the vertical filtration of supercritical CO ₂ . From this we can conclude that the greater the angle of inclination of the wings of the reservoir, the larger the smear zone of CO ₂ .

The practical implementation of the claimed method can be presented with reference to the drawings. The following reference designations were used:

1 - injection wells;

2 - production wells;

3 - water;

4 - methane region;

5 - area of distribution of CO ₂ ;

6 - funnel of depression;

7 - control wells.

In FIG. 6, 7 illustrate the disadvantages of the method closest in technical essence to the claimed method of operation [see Patent for invention RU No. 2532278/11 dated 12.24.2012]. In the lower part of the structure (FIG. 6) is produced through injection of CO ₂ injection wells 1. After the closure of the injection wells 2 starts gas selection. The disadvantage of this method is that part of the natural gas located in the region between the boundary of the gas-water contact (GWC) and the injection region of CO ₂ will not be recoverable, or, under the influence of the discharge pressure, will move to the closing isogypsum and possibly go beyond it (Fig. 7).

To put into practice the claimed method, it is necessary to perform the following. Based on the value of the active volume and the idea of the geometric characteristics of the reservoir, the position of isohypses limiting the active volume is calculated. Isogypsum is defined similarly, limiting the fraction (A, e) of the buffer volume of gas (from the roof). This isogypsum is selected for placement of control wells 7, designed to control the distribution of supercritical CO ₂ in the reservoir. Wells 1 depending on the stage of substitution or are used for the selection process of natural gas, or injection of supercritical CO _2. The location of the wells 1 is selected depending on the shape of the reservoir. If the inequality A × D≤d≤D (Fig. 12) is true, then wells 1 should be placed, if possible, at an equal distance from the center of the reservoir on the longitudinal and transverse axes. In the case of d <A × D, well 1 should be placed, if possible, at an equal distance from the center of the reservoir on the longitudinal axis. In this case, wells 1 should be placed in areas with low gas saturation and closer to GWC to prevent loss of natural gas in the reservoir. In the lower part of the reservoir, natural gas is taken through injection wells 1 (Fig. 8). In this case, a depression funnel 6 is formed in the selection area. After the natural gas extraction is completed, wells 1 are transferred to supercritical СО ₂ injection (Fig. 9). The injection is carried out until the compensation funnel for depression 6 in the region of wells 1 is compensated, or until supercritical CO _{2 is} detected in the control wells 7. Then, natural gas is extracted through production wells 2 (Fig. 10). The selection should be stopped in case of detection of supercritical СО ₂ in the zone of wells 7. In the normal mode, the active volume of natural gas is taken. In the injection season, the active volume of natural gas is injected (FIG. 11). This will make it possible to push supercritical СО ₂ from wells 7 to wells 1. Work on the replacement of natural gas is suspended for a neutral period. During this time, have been monitoring the state of monitoring wells 7 for promotion to them of the supercritical CO _2. In the absence of supercritical СО ₂ in the zone of control wells 7 and if it is possible to replace an additional part of the buffer volume, the selection of natural gas and the injection of supercritical СО _{2 are} carried out according to the above algorithm.

The method of operation of the underground storage of natural gas can significantly improve the quality of the stored gas by reducing the risk of early breakthrough of CO ₂ to the slaughter wells, as well as the risk of extensive mixing zones of natural gas and carbon dioxide. In addition, the proposed method allows more efficient use of UGS facilities by replacing part of the buffer volume of stored natural gas with CO ₂ based on a reasonable choice of the state of aggregation of CO ₂ .

Claims (1)

A method of operating an underground natural gas storage facility, including constructing production wells in the domed part of a reservoir reservoir, cyclic injection into a natural gas storage facility to create buffer and active volumes thereof, and selecting an active volume of natural gas, while carbon dioxide is pumped during operation of the underground gas storage facility ( CO ₂₎ and replace them in the buffer volume natural gas, characterized in that the reservoir is selected from the thermobaric parameters: the reservoir pressure P _pl ≥73,8 bar and layers th temperature T _mp ≥31 ° C, leakproof tire of CO ₂ and constructing injection wells at the periphery of the reservoir and monitoring wells in the intermediate area between the production and injection wells, and in the preparation cycle is carried out through injection wells selected from gas buffer zone volume gas in the case of a water pressure regime before formation water appears in the production of wells, in the case of a gas regime until a predetermined minimum reservoir pressure is reached, then through a pump production wells inject CO ₂ in a supercritical state of aggregation until the initial reservoir pressure is reached, then in the first working cycle the selection of natural gas is carried out through production wells, while the occurrence of supercritical CO ₂ in control wells is controlled, natural gas is taken until the active volume of natural gas, or until supercritical CO ₂ appears in the control wells, then natural gas is pumped through production wells until recovery of a of the active volume of natural gas, then the neutral period is maintained, supercritical CO _{2 is} pumped into injection wells through injection wells to the maximum permissible formation pressure, or until supercritical CO ₂ appears in control wells, after which natural gas is extracted through production wells, supervise the appearance of supercritical CO ₂ in the control wells, and stop the selection when supercritical CO _{2 is} detected in the control wells, and re-injection supercritical CO _{2 is} completely stopped in the reservoir if supercritical CO ₂ is detected in control wells, to compensate for excess above the initial reservoir pressure, the extraction of active natural gas is increased, then the active volume of natural gas is pumped into the third cycle when supercritical CO _{2 is} detected in the control the wells cease to replace the buffer volume of natural gas with supercritical CO ₂ , and the selection and injection of natural gas is performed in the amount of the active volume.

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