RU2778624C1 - Core holder for physical modeling of mass transfer processes in the study of oil displacement by gas - Google Patents

Abstract

FIELD: oil and gas technologies.

SUBSTANCE: claimed device relates to the field of experimental studies of mass transfer processes during filtration of oil with gases on a bulk disintegrated core model of a reservoir bed in a laboratory. The core holder consists of a base, side covers, while the side covers are made tightly adjacent to the base on both sides with bolted connections; a soft metal sealing gasket is placed between the base, the left cover and the right cover; on both sides of the base there are internal spiral channels, left and right, in the central part of the base there is a through passage channel for connecting two spiral channels by means of a bolt-nut connection; at the base of the core holder there is a through hole with the possibility of supplying an injection agent, and in the right spiral channel there is an opposite hole with the possibility of oil and gas output.

EFFECT: possibility of regulating the permeability range by means of the possibility of adjusting the tightening force of the side caps of the core holder.

1 cl, 7 dwg

Description

The claimed invention relates to a device that, when used in a laboratory, makes it possible to conduct experimental studies of mass transfer processes during the filtration of oil and other fluids with gases (at various compositions and proportions) on a bulk disintegrated core model of a reservoir.

Further in the text, the applicant gives the terms and abbreviations that are necessary to facilitate an unambiguous understanding of the essence of the claimed materials and to eliminate contradictions and / or controversial interpretations when performing an examination on the merits.

D (Darcy) is an off-system unit of permeability of porous media, approximately equal to 1 µm² [https://ru.wikipedia.org/wiki/%D0%94%D0%B0%D1%80%D1%81%D0%B8]. Widely used in geology, hydrology and oil and gas production, soil mechanics. The submultiple units of centidarcy (sD) and millidarcy (mD) are often used.

EOR - methods of enhanced oil recovery.

MDS - minimum mixing pressure.

Bulk disintegrated core model - a core crushed to a certain required fraction for packing into a core holder.

At the date of submission of this application, the Applicant examined the existing state of the art, identified technical solutions designed to study cores and bulk core models of the reservoir as a whole and devices used to fix and pack a bulk disintegrated core model, used mainly in laboratory tests.

As is known, at present most of the large fields are at a late, final stage of development, however, more than half of the geological oil reserves remain unextracted. At the same time, the main share of residual reserves is classified as hard-to-recover, of which at least 30% are in low-permeability reservoirs, the development of which requires efficient and cost-effective technologies for enhanced oil recovery.

With suitable applicability criteria, namely: reservoir depth of more than 1500 meters, reservoir thickness from 2.5 to 10 meters, porosity from 10 to 35%, permeability 0.002-0.2 microns ² , oil saturation more than 40%, reservoir temperature from 10 up to 120 °С; as a solution to the problem, gas and miscible agents are mainly used, since the high level of miscibility of gas and oil makes it possible to reduce (suppress) capillary forces [Liang Meng, Antonov S.V., Mishin A.S., Khlebnikov V.N., Vinokurov V.A. Influence of miscibility level on physical modeling of oil displacement by gas (solvent) // Actual problems of oil and gas. - 2016. - 2(14), DOI 10.29222/ipng.2078-5712.2016-14.art10].

When using gas methods to increase the oil recovery factor, it is critical to determine the miscibility conditions of the injected gas and oil. The minimum miscibility pressure (MPP) is the pressure at which a gas becomes miscible with oil of a certain composition at a certain temperature. Under laboratory conditions, the study of this parameter on core models does not allow to fully reveal the oil-displacing characteristics of gas fluids, which is explained by the impossibility of achieving multi-contact miscibility with a short filtration path. Thus, to increase the efficiency of physical modeling of oil displacement by gases, it is necessary to use a device whose length is many times greater than its diameter, filled with a granular medium (sand or other filler). The most common method for determining the minimum miscibility pressure (MMP) is the slim tube method.

In physical modeling, the well-known method provides for the use of thin tubes filled with sand or other material, 8 to 40 m long and 3-10 mm in diameter, providing mass transfer between oil and a displacing gas agent. The study of mass transfer processes using a thin tube began in 1956 and has been intensively developed to the present. At the filing date of this application, various modifications of thin tubes filled with particulate material and having an average absolute permeability in the range of 2-10 D [Zhang, K., Jia, N., Zeng, F., Li, S., Liu, L. A review of experimental methods for determining the Oil-Gas minimum miscibility pressures. Journal of Petroleum Science and Engineering, 2019, V.183, 106366, https://doi.org/10.1016/j.petrol.2019.106366]. Proper particulate materials should be packed into a thin tube to mimic the effect of having a pore space. Silica sands and glass microspheres are the two most common packaging materials for existing thin tubes.

Despite the fact that the known slim tube method is a generally accepted method for determining MDS in the oil industry, there are significant drawbacks, such as the difficulty of creating highly packed thin tubes with an absolute permeability of 1 D or less. A particularly important drawback is the impossibility of adjusting the permeability range of a thin tube and modeling mass transfer processes on a bulk disintegrated core model created by crushing the core of the production object under study.

From the studied state of the art, the applicant identified an invention according to RF patent No. 2685466 "Core holder". The essence of the well-known technical solution is a core holder containing a vertically installed metal pipe with a core sample placed in it, the upper and lower plungers located at the ends of the pipe with sealing mechanisms and pressed against the core sample, while the upper plunger has a through axial channel for supplying a gaseous working agent, and in the lower plunger there is a through axial channel for supplying or discharging a liquid or gaseous working agent, in addition, the upper part of the pipe is equipped with at least three injection fittings for supplying a screening liquid, the horizontal axes of which lie in a plane parallel to the ends of the pipe, and the angles between the axes of adjacent injection fittings are equal to each other, the middle part of the pipe is equipped with at least three fittings for the selection of screening liquid or working agent, the horizontal axes of which lie in a plane parallel to the ends of the pipe, and the angles between the axes of adjacent fittings for the selection of screening fluid liquids or working agent are equal to each other, the lower part of the pipe is equipped with one additional horizontal fitting designed to drain or supply a liquid or gaseous working agent, while shut-off valves are installed on all supply and discharge lines of both the working agent and the screening liquid.

The technical result of the well-known technical solution is the expansion of the functionality of the core holder, providing the possibility of simultaneously modeling the gas-saturated and oil-saturated parts of the formation. The equipment differs in the mechanism and principle of conducting filtration experiments, but is similar in terms of the possibility of using a bulk reservoir model, namely, with the help of the developed core holder, reservoir models are formed (bulk, core or bulk from crushed core material).

A disadvantage of the known device is the impossibility of carrying out studies of mass transfer processes during the filtration of oil and other fluids with gases due to the small length of the core holder, as a result of which it is impossible to obtain the necessary MDS parameters.

There is a patent for utility model RU No. 193039 "Double-shell compression slim-model of a reservoir for studying the processes of fluid interaction in a reproducible porous medium". The essence of the well-known technical solution is a reservoir slim model for studying the processes of interaction of oil with gas in a porous medium, which is a steel tube, the length of which is many times (at least 500 times) greater than its diameter, filled with a granular medium (sand or other filler), saturated with the studied fluids, characterized in that it is supplemented with an outer tube attached to the inner tube with the formation of a cavity between them, into which water or other medium is injected through fittings or other connecting parts to create a crimp pressure on the inner tube, preventing its deformation.

The disadvantage of the known utility model is the lack of a description of the possibility of adjusting the permeability range according to the given values, as well as conducting studies on bulk disintegrated core models of the studied field.

A patent for the invention CN211086017U "Device for experiments with a thin tube" is known. The essence of the known technical solution is an experimental device with a thin tube, consisting of a piston cylinder for pumping oil, a valve, a gas piston cylinder, a pressure generating unit and a backpressure measuring unit, a piston cylinder for oil and gas injection, and a piston cylinder. The pressure generation unit and the backpressure measurement unit are connected in a parallel structure by means of pipelines. The valves are installed in the front and rear pipelines of the oil and gas injection piston cylinder and the piston cylinder in parallel. At the same time, the model of a thin tube between the parallel structure and the counterpressure measurement unit is provided with a connecting hinge, and is also respectively connected to the two ends of the connecting seam by threaded connections.

A more detailed experimental setup is made in the form of a composite thin tube 50 cm long and with an inner diameter of 3.5 mm - 8.0 mm, and the outer surfaces of both ends of the tube body are respectively provided with connecting threads. The essence of the invention lies in the simple design of the plant, it is easy to combine, disassemble and wash, it is also possible to use a special sand packing device, which improves the average density in the thin tube model and avoids the formation of pore material and gas channel discontinuity. When connected in series, the length of the thin tube can vary according to the conditions of the experiment.

The disadvantages of the known technical solution is:

- the risk of system leakage due to the large number of threaded couplings, which complicate the preparation of the tube for testing. When conducting physical modeling for gas EOR in the area of high reservoir pressures (up to 70 MPa), it is necessary to use a minimum of threads to eliminate the leakage of the installation;

- lack of a description of the possibility of adjusting the range of permeability according to the given values, as well as conducting studies on bulk disintegrated core models of the studied field.

Based on the analysis of the studied prior art, the applicant concludes that the identified analogues coincide with the claimed technical solution in various single features in different analogues, as a result of which the prototype in relation to the claimed technical solution has not been identified, therefore, the independent claims are made without a restrictive part.

The technical result of the claimed technical solution is the ability to control the permeability range of a thin tube by varying the granulometric composition of the bulk disintegrated core model with the possibility of adjusting the packaging of the disintegrated model in the core holder by means of the ability to control the tightening force of the side covers of the core holder by using a bolt-nut type connection. The degree of packing of the core material in the core holder is selected based on the observance of the similarity of the reservoir bedding conditions and its reservoir properties of a sample from a real well.

The essence of the claimed technical solution is a core holder for physical modeling of mass transfer processes in the study of oil displacement by gas, consisting of a base, left and right side covers, while the left and right side covers, respectively, are made tightly adjacent to the base on both sides using bolted connections; between the base, the left cover and the right cover there is a sealing gasket made of soft metal with the possibility of ensuring the tightness of the core holder; on both sides of the base there are internal spiral channels left and right, respectively, with the possibility of filling with a bulk core model, in the central part of the base, a through transition channel is made to connect two helical channels, left and right, respectively, by means of a bolt-nut connection; a through hole is made in the base of the core holder with the possibility of supplying an injection agent, and an opposite hole is made in the right spiral channel with the possibility of removing oil and gas.

The claimed technical solution is illustrated in Fig.1 - Fig.7.

Figure 1 shows the base of the declared core holder (top view).

Figure 2 shows the base of the core holder for physical modeling of mass transfer processes (sectional view A-A ).

Figure 3 shows the base of the core holder for physical modeling of mass transfer processes (sectional view B-B ).

Figure 4 shows the side cover of the claimed core holder (top view).

Figure 5 shows the core holder for physical modeling of mass transfer processes (sectional view A-A ).

Figure 6 shows an annealed copper gasket for a core holder for physical modeling of mass transfer processes

Figure 7 presents a Table that shows the results of physical modeling of mass transfer processes in the study of oil displacement by gas at various rates.

Positions in figure 1 - figure 5 denote:

1 - base;

2 - side cover (left);

3 - side cover (right);

4 - spiral channel (left);

5 - spiral channel (right);

6 - transition channel between spirals;

7 - through hole for supplying the injection agent;

8 - through hole for fluid output from the spiral channel;

9 - annealed copper seals (disposable);

10 - a bolt of fastening of covers.

11 - the location of the coupling bolt.

The declared core holder is assembled as follows.

1. A bulk disintegrated core model is prepared by crushing the core taken from the field under study to a certain required fraction.

2. To simulate the pore space, the spiral channel (left) of the prepared bulk disintegrated core model is packed until it is completely filled. Next, the level of the bulk disintegrated core model is leveled using a special scraper and its excess part is removed from the surface of the spiral channels.

3. To create a given permeability, the side cover (left) and the base of the core holder are assembled with a bulk disintegrated core model with the required tightening torque of the bolt-nut fasteners.

4. Before assembly, the sealing surfaces of the side cover (left) are cleaned of dirt, degreased with white spirit according to GOST 3134 or acetone according to GOST 2768 and dried.

5. Before assembly, anti-friction grease is applied to the threaded part of the bolts (studs) and nuts intended for fastening the side cover (left) and the base.

6. Before assembly on the surface of the side cover (left), prepare and install a soft metal seal (mainly copper), and fasteners in the places where the covers are connected. The tightness of the core holder is ensured not only directly by the tightening force of the fasteners, but also by the effect of self-sealing of the gaskets.

7. When assembling, uniformly tighten the fasteners of the side cover (left) and the base in a crosswise sequence until the sealing surfaces of the side covers come into contact with the gasket. At the same time, the gap between the side covers and the base is constantly monitored.

8. In a similar way, prepare and assemble the side cover (right) and base.

9. When disassembling, the fasteners are released in the reverse order of tightening.

Next, the applicant provides a description of the claimed technical solution.

The claimed core holder refers to a device that, when used in laboratory conditions, makes it possible to conduct physical modeling of mass transfer processes during the filtration of oil and other fluids with gases (at various compositions and proportions) on a bulk disintegrated core model. At the same time, due to the variation in the granulometric composition of the core material, it is possible to conduct filtration experiments on a bulk disintegrated core model with an absolute permeability of 1 D or less, created by crushing and packing the core of the studied operational object of the field.

The claimed core holder (Figure 1 - Figure 6) is characterized by a simple design, which facilitates the preparation of the core holder for laboratory research and contributes to a minimal risk of leakage in the device.

In general, the core holder consists of three main parts, namely:

- bases (1),

- left cover (2),

- right cover (3).

In this case, the left (2) and right (3) side covers are made tightly adjacent to the base (1) on both sides using, for example, bolted connections (10). At the same time, between the base (1), the left cover (2) and the right cover (3), a sealing gasket (9) is made of soft metal, for example, copper, with the possibility of ensuring the tightness of the core holder, while with each new experiment of the gasket (9) are replaced with new ones, because they are subjected to dynamic forces and thereby lose their thickness, namely, they are flattened under a compression load by a bolted connection (11) of the bolt-nut type.

At the same time, on both sides of the base (1) there are internal spiral channels left (4) and right (5), respectively, with the possibility of filling with a bulk core model. In the central part of the base (1) there is a through transition channel (6) for connecting two helical channels (4) and (5), which is carried out by means of a bolt-nut connection (11).

A through hole (7) is made in the base of the core holder (1) with the possibility of supplying the injection agent. The spiral channel (5) has an opposite opening (8) with the possibility of oil and gas withdrawal. Through holes for injection agent supply (7) and oil and gas output (8) are mirror-symmetrical along the section A-A and and rotated by 180° relative to each other (see Fig. 2).

Further, the applicant provides a description of the work of the declared core holder.

First, the granulometric composition of the bulk core model is selected according to the specified values of the final permeability.

Next, a bulk disintegrated core model is prepared by crushing the core taken from the field under study to a certain required fraction.

Next, the internal spiral channels of the left (4) and right (5) are prepared, for which each spiral channel of the core holder is packed with a pre-prepared bulk core model using a special scraper. Packing is carried out with the core holder in a horizontal position. The assembly of the core holder is carried out with the required tightening force of the fasteners. The applied force is calculated based on the compliance of the prepared bulk core model with the reservoir properties of the studied field.

Then the core holder is placed in a filtration unit, thermobaric conditions are set, and studies are carried out on the displacement of oil by gas.

At the end of the experiment, the core holder is dismantled, a bulk core model is removed for further analysis of residual oil saturation, changes in permeability and particle size distribution.

At the same time, it should be noted that the spacers need to be replaced with each new experiment. because when applying compressive forces, the gasket will deform (flatten out).

Further, the applicant gives an example of the implementation of the claimed technical solution.

Example 1. Physical modeling of mass transfer processes in the study of oil displacement by gas.

For physical modeling, core samples are taken from one of the deposits in Western Siberia.

A bulk disintegrated core model is prepared by crushing the core taken from the field under study to a fraction of 0.1-0.16 mm.

Next, the internal spiral channels of the left and right are prepared, for which each spiral channel of the core holder is packed with a pre-prepared bulk disintegrated core model. Packing is carried out with the core holder in a horizontal position using a special scraper. The assembly of the core holder is carried out with the required tightening force of the fasteners. The applied force is calculated experimentally, based on the reservoir properties of the reservoir under study.

Next, the core holder is placed in a filtration unit, the reservoir temperature and the injection agent flow rate are set.

Further studies are carried out on the displacement of oil by methane. Research is carried out until the end of oil displacement.

At the end of the experiment, the core holder is dismantled, a bulk disintegrated core model is removed for further analysis of residual oil saturation, changes in permeability and particle size distribution.

The results of the experiment are shown in the Table in FIG. 7.

According to the results shown in the Table, it can be concluded that the claimed core holder provides the possibility of conducting physical modeling of mass transfer processes during the filtration of oil and other fluids with gases (at different compositions and proportions) on a bulk disintegrated core model with a given absolute permeability and using core material the investigated operational object of the field, which confirms the achievement of the claimed technical result.

The claimed technical solution meets the criterion of "novelty" for inventions, because the claimed set of features is not identified from the studied prior art.

The claimed technical solution meets the criterion of "inventive step", because is not obvious to a specialist due to the fact that the claimed design allows the implementation of two new tasks in one installation, which could not previously be implemented on similar devices, or such tasks have not been previously posed in principle, namely, for example, the task of preparing a disintegrated model formation according to the given permeability values, with the possibility of using core samples for grinding the studied field, in the field of studying mass-transfer processes in laboratory conditions, was not feasible, as a result of which the use of the claimed device provides the possibility of obtaining more information about the process of physical modeling of oil displacement by gas, which contributes to an increase the probability of a more accurate determination of the minimum miscibility pressure and the oil-gas displacement ratio for the studied reservoir.

The claimed technical solution complies with the condition of patentability "industrial applicability" for inventions, tk. can be carried out using standard equipment and known techniques.

Claims (1)

Core holder for physical modeling of mass transfer processes in the study of oil displacement by gas, consisting of a base, left and right side covers, while the left and right side covers, respectively, are made tightly adjacent to the base on both sides using bolted connections; between the base, the left cover and the right cover there is a sealing gasket made of soft metal with the possibility of ensuring the tightness of the core holder; on both sides of the base there are internal spiral channels left and right, respectively, with the possibility of filling with a bulk core model, in the central part of the base, a through transition channel is made to connect two helical channels, left and right, respectively, by means of a bolt-nut connection; a through hole is made in the base of the core holder with the possibility of supplying an injection agent, and an opposite hole is made in the right spiral channel with the possibility of removing oil and gas.

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