Air tightness test device with cavity top position detection and cavity top position detection method thereof

Abstract

The application provides a cavity top position detection gas seal test device and a cavity top position detection gas seal test method thereof. The device comprises a variable diameter flange, a nitrogen injection pipeline and a pressure gauge. The method is suitable for the cavity top position detection gas seal test device and comprises the following steps: S1, connecting a salt cave cavity mouth device; S2, increasing nitrogen pressure; S3, measuring a gas halo interface; and S4, drawing a nitrogen pressure-cavity mouth gas halo interface depth curve of the salt cave. The method is simple in operation and can accurately detect the highest position of the salt cave top of a single well and a single cavity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underground salt cavern storage engineering, and particularly relates to a gas seal test device for detecting a top position of a cavity and a method for detecting the top position of the cavity. BACKGROUND

[0002] Due to stratum inclination, there is an obvious partial dissolution phenomenon in the process of water-soluble dissolution of a salt cavity, which causes the highest point of the salt cavity not to be the position where the injection-production well initially enters the cavity. At present, the form of the salt cavity is understood by using a sonar cavity measurement and a three-dimensional seismic test method. Since the limit of the sonar detection equipment, when the form of the underground cavity exceeds the form range that can be detected by the sonar, the sonar cavity measurement cannot detect the highest position of the top of the salt cavity. When the three-dimensional seismic detection is performed, the distribution form of the salt cavity needs to be understood in detail, and the range of the three-dimensional seismic wiring is set in a targeted manner. However, the fracturing range of the fracturing well is difficult to predict, and the distribution of the cavity is also complex and changeable, so the cavity boundary measured by the three-dimensional seismic measurement often exceeds the range of the three-dimensional seismic wiring, causing the highest position of the top of the salt cavity to be undetectable. Meanwhile, the system error of the three-dimensional seismic detection cavity depth also exists.

[0003] Since the depth of the top of the salt cavity is unknown, there is a certain risk in the pressure design of the underground salt cavern storage, and it is also difficult to determine the position of the injection-production well. How to obtain the depth of the top of the cavity has a positive significance. SUMMARY

[0004] To solve the above technical problems, one of the technical solutions of the present application is a gas seal test device for detecting a top position of a cavity, an injection-production pipe string 1 and an annular packer 2 are arranged in the injection-production well, the injection-production pipe string 1 is vertically inserted into the cavity of the salt cavern, and the annular packer 2 is arranged in the gap between the injection-production pipe string 1 and the inner wall of the cavity of the salt cavern. The device is installed at the top of the cavity of the salt cavern, and the device comprises:

[0005] a variable-diameter flange which is installed on the injection-production pipe string 1;

[0006] a gas injection pipeline which is installed on the variable-diameter flange and has one end extending into the injection-production pipe string 1;

[0007] a pressure gauge 3 which is installed on the variable-diameter flange and is used for monitoring the pressure in the injection-production pipe string 1 after gas injection.

[0008] Further, the other end of the gas injection pipeline is connected with an external nitrogen making equipment.

[0009] A gate valve is arranged on the gas injection pipeline and is used for controlling the amount of gas.

[0010] Another technical solution of the present application is a method for detecting a top position of a cavity, which is suitable for the above-mentioned gas seal test device for detecting the top position of the cavity, and the method comprises the following steps:

[0011] S1, the cavity mouth equipment of the salt cave is connected;

[0012] S2, nitrogen injection and pressure increase;

[0013] S3, gas-halide interface measurement;

[0014] S4, drawing the curve of the nitrogen pressure at the cavity mouth of the salt cave and the depth of the gas-halide interface.

[0015] Further, in S1, the downhole preparation is made, the reducing flange, the gate valve, the gas injection pipeline and the pressure gauge 3 are installed at the cavity mouth of the salt cave, the pressure test is carried out on the connecting part of the well mouth equipment, and the qualified pressure test is ensured.

[0016] Further, in S2, the gate valve for gas injection is opened, and nitrogen is injected into the injection and production pipe string 1 through the existing nitrogen making vehicle;

[0017] When the nitrogen is injected into the cavity point of the injection and production pipe string 1, the gate valve for gas injection is closed.

[0018] Further, in S3, the existing optical fiber or neutron logging is lowered into the cavity of the salt cave, and the continuous gas-halide interface depth is read during the process of nitrogen injection and pressure increase.

[0019] Further, in S4, the inflection point of the curve of the nitrogen pressure at the cavity mouth of the salt cave and the depth of the gas-halide interface is the highest position of the cavity top of the salt cave.

[0020] The method has the advantages and positive effects that the method is simple to operate, and the highest position of the cavity top of the single-well single-cavity salt cave can be accurately detected. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a schematic diagram of the gas seal test device for detecting the position of the cavity top;

[0022] Figure 2 It is a schematic diagram of the gas seal test device for detecting the position of the cavity top after nitrogen injection;

[0023] Figure 3 It is a physical process diagram of the gas seal test device for the mathematical model of liquid elastic compression;

[0024] Figure 4 It is a physical process diagram of the gas seal test device for the mathematical model of liquid column pressure;

[0025] Figure 5 It is a pressure gauge monitoring time curve diagram;

[0026] In the figure: 1, injection and production pipe string; 2, annular packer; 3, pressure gauge. DETAILED DESCRIPTION

[0027] To better understand the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0028] Example 1

[0029] like Figures 1-2 As shown, a gas-tightness test device is located at the top of the cavity for detection. The injection-production well contains an injection-production tubing string 1 and an annular packer 2. The injection-production tubing string 1 is vertically inserted into the cavity of the salt cavern. The annular packer 2 is located in the gap between the injection-production tubing string 1 and the inner wall of the salt cavern cavity. The device is installed at the top of the salt cavern cavity and includes:

[0030] A reducing flange, which is installed on injection / production tubing string 1;

[0031] The gas injection line is installed on the reducing flange and one end extends into the injection and production tubing string 1.

[0032] Pressure gauge 3, which is installed on the reducing flange, is used to monitor the pressure inside the injection and production tubing 1 after gas injection.

[0033] Specifically, the pressure gauge used for testing is a high-precision, high-density pressure gauge with an accuracy of 0.0001 MPa, capable of reading data in seconds.

[0034] Furthermore, the other end of the gas injection line is connected to an external nitrogen generator.

[0035] The annular packer 2 is filled with protective fluid.

[0036] A gate valve is installed on the air injection line to control the amount of air entering the system.

[0037] Example 2

[0038] A cavity top position detection method, applicable to the gas-tight test device for cavity top position detection described in Example 1 above, the method comprising:

[0039] S1, Connection of the cavity opening device of the salt cave;

[0040] S2, Nitrogen injection pressurization;

[0041] S3, interface for measuring gaseous brine;

[0042] S4. Plot the curve of nitrogen pressure at the cavity opening of the salt cavern versus the depth of the brine interface.

[0043] Furthermore, in S1, prepare for going downhole, and install a reducing flange, gate valve, gas injection line and pressure gauge 3 at the cavity opening of the salt cavern; perform pressure testing on the connection parts of the wellhead equipment to ensure that the pressure test is qualified.

[0044] Further, in S2, the gate valve of the gas injection is opened, and nitrogen is injected into the injection-production pipe string 1 through the existing nitrogen generator vehicle;

[0045] When the nitrogen is injected into the injection-production pipe string 1 into the cavity point, the gate valve of the gas injection is closed.

[0046] Further, in S3, the existing optical fiber or neutron logging is lowered into the cavity of the salt cavern, and the continuous gas-halide interface depth is read during the process of nitrogen injection and pressure increase.

[0047] Further, in S4, the inflection point of the curve of the nitrogen pressure at the mouth of the cavity of the salt cavern and the gas-halide interface depth is the highest position of the top of the cavity of the salt cavern.

[0048] The working principle is as follows: the salt cavern cavity top highest position detection technology based on the wellhead pressure data of the injection-production well is to uniformly inject nitrogen at the wellhead until the nitrogen and the brine interface approach the wellbore into the cavity point. During the process, the high-pressure gas has two physical effects: the first is to compress the saturated brine; the second is to support the saturated brine column;

[0049] The first effect runs through the entire process and can be a nonlinear elastic compression; the second only exists after the gas-liquid interface is below the top of the cavity, and the effect of the gas begins to support the brine column above the gas-liquid interface. The pressure required for the first physical effect is defined as P1, and the pressure required for the second physical effect is defined as P2.

[0050] As shown in Figures 3-4 , 1, a mathematical model of liquid elastic compression is obtained. The first physical effect is the elastic compression of the liquid, and the mathematical model is:

[0051]

[0052] Wherein, E v is the volumetric compression modulus; dP is the pressure increment.

[0053] The initial state of the brine pressure is 0, and the initial state of the brine volume is V0; the gas pressure for compressing the brine is P1, and the brine volume is V i ; the integral of the formula can be obtained as:

[0054]

[0055] Let ΔV = V i -V0, substitute the above formula to obtain

[0056]

[0057] The is expanded in series

[0058]

[0059] Since the volume of brine in the wellbore is a small amount compared to the overall volume of brine, in the case of a small amount, a small amount of the second order or more can be ignored, and the following equation is obtained

[0060]

[0061] 2, obtain the mathematical model of the liquid column pressure, the second physical action is the support of the liquid column pressure, and the mathematical model is:

[0062] P2=pgAH

[0063] AH=H i -H0

[0064] Where: p is the saturated brine density, 1209.6 kg / m 3 ; g is the acceleration of gravity, m / s 2 ; H i is the depth of the gas-liquid interface, m; H i is the depth of the cavity top, m; AH is the height difference between the gas-liquid interface and the cavity top, m;

[0065] When the gas-liquid interface H i is above the cavity top H0, only the elastic compression of the liquid; when the gas-liquid interface H i is below the cavity top H0, in addition to the elastic compression of the liquid, there is also the support of the liquid column pressure, that is

[0066]

[0067] The data-intensive pressure monitoring time curve can be obtained under the pressure gauge monitoring data as shown in Figure 5 When the gas-liquid interface crosses the cavity top, the pressure value monitored will change obviously at a certain time Ti due to the difference in pressure equation. At that moment, the gas-liquid interface crosses the cavity top. The gas-liquid interface data monitored at that moment is the highest position of the salt cavern cavity top.

[0068] The above embodiments of the application are described in detail, but the content described is only the preferred embodiments of the application, and cannot be considered as limiting the scope of the application. Any equivalent changes and improvements within the scope of the application should still be included in the scope of the patent.

Claims

1. A method of cavity top position detection, characterized by: The method comprises: S1, connecting the air tightness test device at the cavity mouth of the salt cave; the injection-production well is provided with an injection-production pipe string (1) and an annular packer (2), the injection-production pipe string (1) is vertically inserted into the cavity of the salt cave; the annular packer (2) is located in the gap between the injection-production pipe string (1) and the inner wall of the cavity of the salt cave; the air tightness test device is installed at the top of the cavity of the salt cave, and the air tightness test device comprises: a variable diameter flange installed on the injection-production pipe string (1); a gas injection pipeline installed on the variable diameter flange and extending into the injection-production pipe string (1) at one end; a pressure gauge (3) installed on the variable diameter flange for monitoring the pressure in the injection-production pipe string (1) after gas injection; S2, nitrogen injection and pressure increase; S3, gas-halide interface measurement; S4, drawing a curve of the nitrogen pressure at the cavity mouth of the salt cave and the gas-halide interface depth; In S4, the inflection point of the curve of the nitrogen pressure at the cavity mouth of the salt cave and the gas-halide interface depth based on the monitoring data of the pressure gauge (3) and the gas-liquid interface is the highest position of the top of the cavity of the salt cave.

2. The chamber top position detection method of claim 1, wherein: The other end of the gas injection pipeline is connected with an external nitrogen making equipment; a gate valve is arranged on the gas injection pipeline for controlling the amount of gas.

3. The chamber top position detection method of claim 2, wherein: In S1, the downhole preparation is completed, the variable diameter flange, the gate valve, the gas injection pipeline and the pressure gauge (3) are installed at the cavity mouth of the salt cave; the wellhead equipment connection part is pressure tested to ensure that the pressure test is qualified.

4. The chamber top position detection method of claim 3, wherein: In S2, the gas injection gate valve is opened, and nitrogen is injected into the injection-production pipe string (1) through the existing nitrogen making vehicle; When the nitrogen is injected into the cavity point of the injection-production pipe string (1), the gas injection gate valve is closed.

5. The chamber top position detection method of claim 4, wherein: In S3, the existing optical fiber or neutron logging is lowered into the cavity of the salt cave, and the continuous gas-halide interface depth is read during the nitrogen injection and pressure increase process.

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