RU2386805C1 - Creation method of low-premeability of screen in porous medium - Google Patents

Abstract

FIELD: oil-and-gas production.

SUBSTANCE: it is implemented preparation of injection well in insulated area by path close to roof cladding configuration of insulated area of stratum. Then it is pumped into it solution of foam maker with following feeding of gas for foaming. It is defined minimal horizontal lateral dimension of screen from conditions of filtration through the screen of gas and/ or water considering pressure gradient at the boundaries of screen at the period equal to period maximal pumping into gas storage or maximal permissible withdrawal of gas from particular storage. Minimal vertical dimension if screen is considered equal to value which is not less than maximal dimension from roof of formation up to gas-water contact in the area of screen creation. In preference it is implemented injection well making, path of which is normal to vector of average speed of formation fluid in isolated area of stratum. Preferentially it is also implemented making of inclined and/or horizontal injection well.

EFFECT: reliability growth of operating characteristics of screen, reduction of foam former consumption and gas amount, used for foaming and consumptions for wells drilling.

3 cl, 3 tbl, 1 ex, 3 dwg

Description

The invention relates to methods for creating a low-permeability screen in a porous medium in an isolated zone of a formation when storing gas in an underground storage in porous reservoirs, and in particular, to methods for restricting the undesirable movement of formation fluids in porous media, and can be used in the oil and gas industry.

The operation of underground gas storages (UGS) in reservoirs is significantly complicated due to gas flows beyond the design hypsometric marks on zones and interlayers of the reservoir with abnormally high reservoir properties, as well as due to premature flooding of production wells during gas extraction from UGS, occurring:

- due to insufficient complete replacement of water in a porous medium by gas in the vicinity of the well when the latter is injected into the reservoir of the UGSF and squeezed out of water from low-permeable, non-dried interlayers into the wellbore during subsequent gas extraction from the UGS;

- due to the rise of water to the bottom of production wells through lithological "windows";

- due to the pressure drop in the reservoir in the vicinity of the production well and, as a consequence, cone-shaped breakthroughs of produced water from the underlying aquifers;

- due to the massive introduction of formation water into the gas-saturated region of the UGS reservoir in the presence of highly permeable zones near the gas-water contact (GWC).

To eliminate these complications, leading to a decrease in the efficiency of operation of underground gas storage wells and posing a threat to the ecological state of the environment, in-situ low-permeability screens are created.

The theoretical basis for creating in-situ screens is to reduce the phase permeability of the porous medium for the formation fluid and gas when injecting through the wells into the reservoir zone to be isolated, shielding fluids of various nature - cement mortars, water repellents, foam, emulsions, etc.

The most effective tool for creating in-situ screens in order to isolate the undesirable movement of water and especially gas is the formation of foam in a porous medium from a solution of a foaming agent based on a surfactant and gas. According to the results of laboratory studies presented in the monograph (Operation of underground gas storages., Karimov MF, M .: Nedra, 1981), the foam formed in the reservoir from a solution of foaming agent and gas is a nonequilibrium disperse system and, depending on surfactant concentration in a solution and gas saturation of a porous medium can decrease the phase permeability of a porous medium by several orders of magnitude, especially for a gas.

There is a method of creating a screen by injecting a foaming solution into a chain of wells in the zone of the alleged gas leak in the reservoir (US 3330352, 1967, US No. 3393738, 1968). According to the specified method, as a result of mechanical mixing of the foaming agent solution and the gas flow in the formation to be isolated, a foam is formed in the porous medium, which has insulating properties. The recommended concentration of surfactant in the foaming agent solution is from 0.001% to 10 wt.%. In order to increase the stability of the foam formed in the formation, a thickener is added to the foaming agent solution. In this case, the foaming agent solution is injected into the formation in a volume sufficient to form a continuous screen in two portions, the surfactant concentration in the first portion being from 1% to 10 wt.%, And in the second from 0.001% to 1 wt.%. This method has the following disadvantages: when injecting a foaming agent solution into all the wells of the chain, very large volumes of solution must be pumped to obtain an acceptable result. The injection of a foaming solution into a chain of wells with a constant flow rate leads to an increase in reservoir pressure. To maintain a constant flow rate, it is necessary to increase the discharge pressure, which is not always feasible, and reducing the flow rate increases the time required to create a screen in the formation.

There is a method of creating a screen in the reservoir, in which a foaming solution with a surfactant concentration of 0.01-5 wt.% Is pumped into injection wells, alternating with discharge wells (US No. 3,306,354, 1967 and US No. 3379260, 1968). At the same time, the unloading wells are left open and the formation of a continuous barrier is controlled by the liquid pouring out from them, based on the control of the surfactant concentration in this liquid.

The described method of creating a screen is more rational due to the ability to control an excessive increase in reservoir pressure and to obtain a continuous barrier from the foaming solution in the reservoir due to the presence of discharge wells. However, this method is also characterized by the above disadvantages, in addition, it also lacks recommendations for determining the optimal volume of a foaming agent and gas solution necessary to create a screen.

Closer to the described invention is a method of creating a foam screen (barrier) in the formation during underground storage of gas (SU No. 1385438, 1986). According to this invention, the foaming agent solution is pumped into the formation in the zone of the alleged isolation of the gas flow through alternating injection and discharge wells. At the first stage, the solution is pumped into a series of injection wells alternating with discharge wells until a foaming solution appears in the liquid taken from the discharge wells, and the discharge rate of the discharge wells must exceed the injection rate. After the appearance of the solution in the discharge wells, the injection wells are stopped and the foaming solution is pumped into the discharge wells, the volume of the solution injected in the second stage being 2/3 of the volume of the solution injected into the formation in the first stage.

The disadvantages of the method are the need to use a large number of wells with a high flow rate of the foaming agent and the amount of gas used for foaming to provide a relatively reliable overlap of the project site. Moreover, the known method does not fully solve the issues of monitoring the reliability of overlapping of the isolated area, the issues of screen propagation beyond the extreme wells. In addition, this method does not allow to determine the volumes of gas injected into the wells necessary to create a stable screen.

The objectives of the described invention are:

- improving the reliability of restricting the movement of gas volume in order to prevent gas leaks during storage in reservoirs within the calculated (design) hypsometric marks;

- determination of the volume of gas injected after the solution to ensure a stable screen;

- preventing the invasion of produced water into an artificial gas reservoir in order to extend the period of anhydrous exploitation of the underground gas storage (UGS).

The tasks are solved by creating a low-permeability screen in the isolated zone of the formation when storing gas in an underground storage facility by posting an injection well, pumping a foaming solution into it, followed by supplying gas for foaming, in which according to the invention the injection well is guided in an isolated zone along a path similar to the configuration of the roof of the isolated zone of the formation, while the minimum horizontal transverse screen size is determined from the filtration conditions through the screen of gas and / or water, taking into account the pressure gradient at the boundaries of the screen for a period equal to the period of maximum injection into the gas storage or the maximum allowable gas withdrawal from this storage, and the minimum vertical size of the screen is taken to be at least equal to the maximum distance from the formation roof to gas-water contact in the screen creation zone.

In this case, an injection well is preferably produced, the path of which is normal to the average velocity vector of the formation fluid in the isolated zone of the formation.

Preferably, an inclined directional and / or horizontal injection well is also wired.

The technical result achieved in this case is to increase the reliability of the operational characteristics of the screen by increasing the continuity of the screen, to reduce the consumption of foaming agent and the amount of gas used for foaming, as well as the cost of drilling wells.

The described method is carried out as follows.

To create a low-permeability screen, the zone in which it is necessary to create a screen is determined (for example, along the periphery of the UGS reservoir or in the lithological “window”). Next, mark the location of the axes of the future screen and conduct injection (drilling) of the injection well in the isolated zone, the path of which is similar to the configuration of the roof of the isolated zone of the formation and, preferably, normal to the average velocity vector of the formation fluid in the isolated zone. In this case, a directional and / or horizontal well is posted. The well is cased and perforated in the interval of the isolated zone.

The calculated volume of the foaming agent solution is pumped into this well, followed by the solution, the compressed gas is pumped in an amount equal to 3-5 volumes of the injected solution under reservoir conditions.

The theoretical and calculated basis for the creation of low-permeability screens is the empirical dependences of the relative phase permeabilities, which have the following form (Karimov MF Operation of underground gas storages, M .: Nedra, 1981, p. 104):

f _W (s, C) = 0, with: 0.8 <C≤1;

f _g (s, C) = 0, when: 0 <s≤0.1;

a = 3.5 + 12ln [1+ (100 s) ^1.5 ], where

s is the gas saturation of the porous medium, dimensionless quantity;

With the concentration of the foaming surfactant, wt.%;

f _W - relative phase permeability of the porous medium in liquid, dimensionless quantity;

f _g - the relative phase permeability of the porous medium in gas, dimensionless quantity.

As a foaming agent solution, solutions of various surfactants are used. It is more preferable to use a solution of synergistic surfactant compositions consisting of a basic foaming non-ionic surfactant and auxiliary anionic surfactant in produced water, for example a composition consisting of a main foaming non-ionic surfactant, for example, ethoxylated alkyl phenol grade OP-7 or OP-10, and auxiliary anionic surfactant in the form of sulphite-alcohol stillage (PRS). When preparing the solution, it is important to use produced water of the horizon where the screen is planned to be created. This ensures maximum preservation of the strength and structure of the reservoir.

It is known that the main factor affecting surfactant losses in the filtration flow of the foaming agent solution in the formation is adsorption. The degree of adsorption depends on the individual properties of the surfactant and minerals that make up the rock. In this regard, the determination of the concentration of surfactants in the foaming agent solution necessary to create an effective screen is carried out taking into account the adsorption properties of the porous medium and surfactants (Table 1). The presence in this composition of anionic surfactant SSB due to its best adsorption on the surface of the rock (Hydrodynamics and filtering of single-phase and multiphase flows, Proceedings of the Moscow Institute of Chemical Economy and State Design named after IM Gubkin, M .: Nedra, 1972, p. 76) provides a synergistic effect - reduction losses of the main surfactant up to 60 wt.%. In the synergistic composition used in this case, it is preferable to use these surfactants in a ratio of 1: 1 by weight. The concentration of the composition in produced water is 0.6% -1 wt.%.

Table 1
A number of preferred applicability of surfactants to create screens depending on the salinity of formation water Substitution of a surfactant solution in the formation water of the sodium bicarbonate type with mineralization M = 0.1% gas. Critical concentration, C *, wt.% Substitution of a surfactant solution in produced water of calcium chloride type with mineralization M = 15% gas. Critical concentration C *, wt.% OP-10DC 0.3 OP-10DC 0.5 OP-7 0.3 OP-10SNHK 0.5 Arkopol 0.3 OP-7 0.5 Prevotsell WON 0.3 Arkopol 0.5 Prevotsell WOF100 0.3 Terzhitol 0.5 OP-10SNKhK, Synterol AFM-12 0.3 Prevotsell WOF100 0.5 Terzhitol 0.3 Lissapolis 0.5 Prevotsell EO 0.3 Prevotsell EO 0.5 Prevotsell fo 0.3 Prevotsell fo 0.5 Prevotsell FPS 0.3 Prevotsell FPS 0.5 PRS 1,0 PRS 2.5

The experimental values of the front gas saturation and the values calculated using formulas (1) and (2) are shown in Fig. 1.

From the presented materials it follows that the formation of foams - nonequilibrium disperse systems in a porous medium provides an increase in gas saturation already at the displacement front to 0.7-0.8. In this case, the phase permeability for water is also reduced. Therefore, nonequilibrium disperse systems can be effectively used both for shielding the gas volume from the overflow beyond the limits of a certain isogypsum, and for shielding the intrusion of water into the gas-saturated volume of underground gas storage facilities.

In the described invention, improving the reliability of the overlap of the project site and reducing the cost of creating an in-situ screen are essential.

The main parameter of the screen, determining the effectiveness of its functioning, is the screen width - the minimum horizontal transverse screen size. The width of the screen is determined based on the fact that a gas or water particle should be filtered through the screen during time T (equal to the part of the injection or extraction cycle), which is technologically justified from the condition of reliable isolation of gas flows outside the UGS during the period of maximum gas injection or invasion of regional water into gas-bearing region during the period of maximum allowable gas extraction during cyclic operation of underground gas storage facilities. Depending on the geological and technological features of the underground gas storage facilities, the time T is about 90 days.

Screen width, i.e. the necessary (minimum) transverse dimension l, for reliable isolation of the gas volume is determined from the filtration conditions taking into account the pressure gradient at the borders of the screen from the expression:

where P ₁ and P ₂ - the value of the pressure at the boundaries of the screen, MPa; k _g - phase gas permeability coefficient, m ² ; m — porosity, fractions; µ _g is the viscosity of the gas in reservoir conditions, MPa · s.

For particles of water that is filtered through a screen into a gas-bearing zone, the required screen width is determined from the expression:

here k _in - phase gas permeability coefficient for water, m ² ;

µ _in - viscosity of produced water in the reservoir, MPa · s.

Using these formulas, setting the required screening time for a gas volume or intruding formation water determines the width of the screen.

The calculations made using the main fishing characteristics of Gazprom’s underground storage facilities show that the maximum screen width for isolating the gas volume is 19–20 m, and the screen width of 9–10 m is sufficient for isolating intruding water. A detailed calculation of the screen width given in the example.

The minimum vertical screen size h (thickness) is taken to be equal to a component of at least the maximum distance from the formation roof to the gas-water contact in the isolated zone, which provides the design capacity of the underground gas storage facility.

The amount of solution required to create a screen of length L, width l and thickness h is determined from the following expression:

where L is the screen length, m;

m — porosity, fractions;

s — front saturation, dimensionless quantity;

- коэффициент Викке, безразмерная величина;

- Wicca coefficient, dimensionless quantity;

r _ekp - the equivalent radius of the horizontal screen depending on the screen width l, m and its thickness h, m, is determined from the following expression:

Frontal saturation s is determined depending on the selected mineralization of produced water and concentration according to the graphs shown in figure 1.

The Wicca coefficient is determined by the expression σ ² = C / (C + α _max ),

where C, α _max - respectively, the initial concentration of surfactants in the solution and the maximum adsorption of surfactants on the surface of the reservoir, wt.%.

Table 2 shows the values of the Wicca coefficient for solutions of ethoxylated alkyl phenols in formations of different porosity.

table 2 OP10 SNHK C, wt.% 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 one porous medium m = 0.15 0.20 0.31 0.40 0.48 0.53 0.58 0.61 0.64 0.67 0.69 m = 0.20 0.26 0.39 0.49 0.56 0.62 0.66 0.69 0.72 0.74 0.76 m = 0.25 0.32 0.46 0.56 0.63 0.68 0.72 0.75 0.77 0.79 0.81 Wof-100 C, wt.% 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 one porous medium m = 0.15 0.11 0.16 0.21 0.25 0.29 0.32 0.35 0.38 0.40 0.43 m = 0.20 0.15 0.22 0.27 0.32 0.36 0.40 0.43 0.46 0.49 0.52 m = 0.25 0.19 0.27 0.33 0.38 0.43 0.47 0.50 0.53 0.56 0.59 Won C, wt.% 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 one porous medium m = 0.15 0.08 0.13 0.16 0.19 0.23 0.26 0.29 0.32 0.35 0.37 m = 0.20 0.11 0.17 0.22 0.25 0.29 0.33 0.37 0.40 0.43 0.46 m = 0.25 0.15 0.21 0.27 0.31 0.36 0.40 0.44 0.47 0.50 0.53

Compounding the PRS with a concentration of 0.3% by weight allows you to reduce the concentration of the main surfactant by 40%.

The volume of gas that must be pumped after the solution under normal conditions is

Where

V _solution - volume of solution, m ^3,

P _PL - reservoir pressure, MPa,

P _atm - atmospheric pressure, MPa.

The amount of the main surfactant in the foaming solution, M _DOS (kg), is determined from the expression:

Where

With ₀ - the concentration of the main surfactant, wt.%,

V _pact. - the estimated volume of the foaming solution, m ³ .

The amount of synergistic components in the foaming solution, M _syner. (kg) is determined from the expression:

Where

With ^C is the concentration of the synergistic component, wt.%,

V _solution - the estimated volume of the foaming solution, m ³ .

Figure 1 shows the values of the frontal saturation when replacing surfactant solutions with gas. Designations: M = 1% - substitution of surfactant solutions in the formation water of the sodium bicarbonate type with a salinity of 1% by weight; M = 15% - substitution of surfactant solutions in produced water of calcium chloride type with a salinity of 15% by weight.

Figure 2 presents a plan view of the UGS facility with an indication of the location of the screen on the periphery of the UGS facility, the contour of the GWC, production and observation wells, and iso gypsum, providing the design capacity of the UGS facility, L is the estimated length of the screen.

Figure 3 presents the geological profile of the UGS facility with the roof of the geological trap, GVK on isogypsum, providing the design volume of the UGS facility, and the location of the screen on the periphery of the UGS facility along section AA of Fig.2. Legend: l - screen width, h - screen thickness.

EXAMPLE

In an isolated zone of a formation, a directional and horizontal injection well is drilled, the path of which is similar to the configuration of the roof of the isolated zone of the formation and normal to the average velocity vector of the formation fluid in the isolated zone. The well is cased and perforated in the interval of the isolated zone.

Determine: screen size, solution volume and mass of surfactants required to create a screen.

Initial data

The length of the shielded zone (trough, lithological window, peripheral abnormally highly permeable zone) L = 300 m

Depth N = 1000 m.

Produced water of calcium chloride type according to Sulin with a total salinity of M = 150 g / l.

The reservoir pressure varies between 8-10 MPa, i.e. maximum screen load is 2 MPa.

The thickness of the screen in the isolated zone h = 10 m.

Permeability k = 0.65 · 10 ^-12 m ² .

Porosity m = 0.25.

The viscosity of the gas is 0.014 MPa · sec.

The viscosity of the produced water is 1.8 MPa · sec.

1) According to table 1, the main foaming surfactant, for example, OP-10, with a critical concentration of higher than 0.5% is selected and the synergistic component of the surfactant is added - 0.5% PRS.

2) From the curves shown in figure 1, determine the value of the frontal saturation s depending on the adopted critical concentration, in this case, component s = 0.7.

3) Using formulas (1) and (2), the relative permeabilities for gas and liquid are determined at s = 0.7:

k ^* _g = 0.0001, k ^* _w = 0.003, therefore

k _g = 0.0001 · 0.65 · 10 ^-12 m ² and k _w = 0.003 · 0.65 · 10 ^-12 m ² .

4) Calculate the design width (transverse size) of the screen l.

The transverse screen size l in the synclinal trough (or in the lithological window, or in the peripheral area of the underground gas storage facility) is determined from the condition of gas passing through the screen during time T during gas injection and edge or bottom water during the period of the maximum allowable gas extraction from the underground gas storage facility.

The value of l is determined from expression (3), assuming that the gas filtration is steady and the screen cross section is constant:

where P ₁ and P ₂ - the value of the pressure at the boundaries of the screen, MPa; k _g - phase gas permeability coefficient, m ² ; m — porosity, fractions; µ is the viscosity of the gas in reservoir conditions, MPa · s.

For particles of water filtered through a screen into a gas-bearing zone, the minimum screen width l is determined by formula (4) under the same conditions:

Thus, the width of the screen created to prevent gas overflows has a twofold margin for isolating formation water.

Using the formula (6) for a given thickness h = 10 m and a calculated screen width of 20 m, determine the radius of the horizontal screen equal to 10.63 m.

The formula (5) determines the required volume of the solution. The latter is a value equal to 20516 m ³ . By the formula (8) determine the mass of the foaming agent necessary to create a screen. The indicated value is equal to 102 tons. When using a 1% surfactant solution, 14232 m ³ and 142 tons, respectively, are obtained. The formula (7) determines the necessary amount of gas to create a stable screen.

Table 3 presents the comparative results of calculating the consumption of materials when creating a low-permeability screen according to the known method and the described invention.

Table 3 Known method Proposed Technical Solution No. p / p Number of wells, units The volume of the solution, V, m ³ Surfactant mass, tons Gas volume, million
^Nm3 Number of wells, units The volume of the solution, V, m ³ Surfactant mass, tons Gas volume, million
nm ³ one 3 75,000 375 30,0 one 20516 102 8.21 2 3 68333 342 27.3 one 14232 142 5.69

From the data shown in Table 3, it follows that when carrying out the method according to the invention with a screen width of 20 m, the flow rate of the solution is from 14232 to 20516 m ³ , the foaming agent is from 102 to 142 tons, whereas in the known solution with the same screen width, the flow rate of the solution makes from 68333 to 75000 m ³ , the frother's expense makes from 342 to 375 tons. The gas flow rate, as well as the flow rate of the solution and surfactant according to the invention is several times lower than that of the known solution.

Thus, the method according to the invention allows to reduce the consumption of foaming agent and the amount of gas used for foaming, as well as significantly reduce the cost of drilling wells due to the reduction in the number of required wells to one.

Claims (3)

1. A method of creating a low-permeability screen in a porous medium in an isolated zone of a formation when storing gas in an underground storage by conducting an injection well, pumping a foaming solution into it followed by supplying gas for pricing, characterized in that the injection well is guided in the isolated zone along a path similar to the configuration of the roof of the isolated zone of the reservoir, while the minimum horizontal transverse screen size is determined from the filtering conditions through the screen of gas and / or water with Chet pressure gradient at the boundaries of the screen for a period equal to the period of maximum injection into the gas storage or maximum gas withdrawal from this repository, and the minimum vertical size of the screen is determined to be a value of not less than the maximum distance from the top of the formation to gas-water contact in the area of creation screen. 2. The method according to claim 1, characterized in that the injection well is conducted, the path of which is normal to the medium velocity vector of the formation fluid in the isolated zone of the formation. 3. The method according to claim 1, characterized in that they produce a directional and / or horizontal injection well.

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