A method of determining the upper edge of a communication salt cavern access

Abstract

The application discloses a method for determining the upper edge of a communication salt cavern channel, comprising the following steps: performing a sonar cavity measurement operation on two dissolved cavities of a communication well, taking the well with a larger cavity bottom depth as a gas injection well, and taking the well with a smaller cavity bottom depth as a brine discharge well; injecting a liquid for dissolving salt mines into the gas injection well and the brine discharge well to form brine; lowering a test pipe string into the gas injection well until the test pipe string contacts the bottom of the dissolved cavity of the gas injection well, and recording the test pipe string lowering depth L; injecting nitrogen into the test pipe string lowered in the step three, so that the gas enters the gas injection well, and the annulus between the gas injection well and the test pipe string is sealed. Compared with the prior art, the application can determine the height interval of the upper edge of the communication channel between the gas injection well and the communication well, so that the gas-liquid interface height is higher than the height interval of the upper edge of the communication channel when natural gas is injected, and then natural gas leakage caused by the natural gas entering the brine discharge well through the communication channel is avoided, so that the gas injection safety is improved.

Description

Technical Field

[0001] This invention relates to the field of salt cavern gas injection technology, and in particular to a method for determining the upper edge of a connecting salt cavern channel. Background Technology

[0002] like Figure 1 The two salt caverns shown can be used to store natural gas. The storage method is to inject natural gas into the injection well and discharge brine from the discharge well. During the injection process, the gas-liquid interface of the injection well will gradually decrease. The more the interface decreases, the more natural gas can be stored. However, when the gas-liquid interface is lower than the upper edge of the channel, gas will leak out from the discharge well, causing danger.

[0003] In actual production, the free volume of the salt cavern and the bottom of the salt cavern can be monitored by sonar instruments. However, the upper edge of the channel cannot be monitored. This makes it impossible to determine the position of the gas injection interface of the gas injection well, and thus impossible to maximize gas injection. How to determine the position of the upper edge of the channel is the problem that this patent aims to solve. Summary of the Invention

[0004] The main objective of this invention is to provide a method for determining the upper edge of a connecting salt cavern channel, which can determine the height range of the upper edge of the connecting channel between the gas injection well and the connecting well, thereby ensuring that the gas-liquid interface height is higher than the height range of the upper edge of the connecting channel when natural gas is injected, thus preventing natural gas from entering the brine discharge well through the connecting channel and causing natural gas leakage, thereby improving gas injection safety.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for determining the upper edge of a connected salt cavern channel, comprising the following steps: Step 1: Perform sonar cavity probing on the two cavities of the connected well, designating the well with the greater cavity bottom depth as the gas injection well and the well with the smaller cavity bottom depth as the brine discharge well; Step 2: Inject liquid to dissolve the salt ore into the gas injection well and the brine discharge well to form brine; Step 3: Run a test string into the injection well until the test string contacts the bottom of the injection well cavity, and record the depth L of the test string. Step 4: Inject nitrogen into the test string that was lowered in Step 3, so that the gas enters the injection well and seals the annulus between the injection well and the test string. Step 5: Based on Step 4, drain the brine from the brine well and observe whether there are air bubbles in the brine. If there are no air bubbles, it proves that the upper edge of the channel connecting the gas injection well and the brine drain well is below the bottom of the test string. If there are air bubbles, it proves that the upper edge of the channel connecting the gas injection well and the brine drain well is above the test string. Step Six: When the brine discharged from the brine well contains air bubbles, the test string should be pulled up and the operations of Steps Four and Five should be repeated until the brine discharged from the brine well does not contain air bubbles. Record the position L1 of the bottom of the test string at this time, and then pull out the test string to remove it from the gas injection well. Step 7: After the injection and production of the gas injection well is completed, a gas-water interface detector is installed in the injection and production tubing, and natural gas is injected through the injection and production tubing to allow natural gas to enter the gas injection well. The gas-water interface detector is used to monitor the gas-water interface position of natural gas and brine in real time to ensure that the real-time monitored gas-water interface position is above L1 to ensure gas injection safety.

[0006] Furthermore, in step four, the pressure of nitrogen injected into the test column is X MPa greater than the liquid column pressure at depth L, where X is a constant ranging from 0.1 to 5.

[0007] Furthermore, the formula for calculating the nitrogen injection pressure is P=0.0098*ρ*L+X, where: P is the nitrogen injection pressure, in MPa; ρ is the brine density, in g / cm3; and L is the depth of the tubing, in m.

[0008] Furthermore, the formula for calculating the nitrogen injection volume is Q = a * V * P / P 0， In the formula: V is the volume of the tubular column, in meters. 3 P0 is standard atmospheric pressure, and a is a constant with a value range of 3-5.

[0009] Furthermore, the liquid in step two is either water or unsaturated brine.

[0010] Furthermore, the formula for calculating the bottom position L1 of the test tube is L1=LY*n, where n is the number of times the test tube is lifted, Y is the height of lifting the test tube, and the distance of lifting the test tube is the same each time.

[0011] Furthermore, in step five, samples are periodically taken from the brine discharge pipeline of the brine discharge well, and the presence of air bubbles in the brine discharge well is determined by observing whether the sample brine contains air bubbles.

[0012] Furthermore, when the sample brine contains air bubbles, a gas analyzer is used to detect whether the gas contained in the air bubbles is nitrogen.

[0013] Furthermore, the brine sampling interval is 0.5 hours to 1 hour, and the sampling cycle is 24 hours.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention can determine the height range of the upper edge of the connecting channel between the injection well and the connecting well, thereby ensuring that the height of the gas-liquid interface is higher than the height range of the upper edge of the connecting channel when natural gas is injected, thus preventing natural gas from entering the brine discharge well through the connecting channel and causing natural gas leakage, thereby improving the safety of gas injection. Attached Figure Description

[0015] Figure 1 This is a structural diagram of the gas injection well, brine discharge well, and connecting passage.

[0016] Figure 2 This is a schematic diagram of the test string being lowered into the gas injection well according to the present invention. Detailed Implementation

[0017] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments. Example

[0018] Select a pair of connected wells and use sonar to detect the morphology and volume of the cavity, the depth of the cavity top and the depth of the cavity bottom. The well with the larger cavity bottom depth is used as the gas injection well and the well with the smaller cavity bottom depth is used as the brine discharge well. Then, inject clean water or unsaturated light brine into the gas injection well and the brine discharge well, so that the salt minerals in the cavity of the gas injection well and the brine discharge well dissolve and form saturated brine. Using a workover rig, the test string is lowered into the injection well until its bottom tip contacts the bottom of the injection well's cavity. At this point, the depth L of the test string is recorded. Nitrogen is then injected into the injection well through the test string, and the annulus between the injection well and the test string is sealed. The nitrogen will then be transported to the bottom of the injection well. If the upper edge of the connecting channel between the injection well and the brine discharge well is located below the bottom of the injection well's cavity, the nitrogen will float due to its lower density than the brine and will not be able to enter the brine discharge well through the connecting channel. In this case, the injection well can be filled with natural gas, preventing natural gas from entering the brine discharge well through the connecting channel and causing a natural gas leak. If the brine sample discharged from the brine well contains air bubbles and nitrogen is detected by a gas analyzer, the upper edge of the surface connecting channel is located above the bottom opening of the test string. In this case, the test string needs to be lifted by the workover rig, and the brine sample discharged from the brine well needs to be tested again to determine whether nitrogen-containing air bubbles are present. If nitrogen-containing air bubbles are still present, the above steps are repeated until nitrogen-containing air bubbles are no longer present in the brine sample. At this time, the height L1 of the bottom opening of the test string should be recorded. If the brine sample contains air bubbles but no nitrogen is detected, the sampling and testing time will be delayed until air bubbles containing nitrogen are detected or the brine sample does not contain air bubbles.

[0019] Since the test string is lifted to the same height each time by the pipe repair machine, the value of L1 is calculated using the formula L1=LY*n, where L is the depth of the test string, n is the number of times the test string is lifted, and Y is the height of the test string being lifted. Since the height of the upper edge of the connecting channel is lower than L1, when injecting natural gas into the injection well, it is necessary to ensure that the gas-liquid interface height is higher than L1 to ensure that natural gas cannot enter the brine discharge well through the connecting channel, thereby improving safety.

[0020] When injecting nitrogen into the test string, ensure that the pressure of the injected nitrogen is greater than the liquid column pressure at depth L. This allows the nitrogen to be expelled from the test string and enter the injection well. The formula for calculating the injected nitrogen pressure is P = 0.0098 * ρ * L + X, where: P is the nitrogen injection pressure in MPa; ρ is the brine density in g / cm³. 3 L is the depth of the tubing insertion, in meters. The formula for calculating the nitrogen injection volume is Q = a * V * P / P 0， In the formula: V is the volume of the tubular column, in meters. 3 P0 is standard atmospheric pressure, and a is a constant with a value range of 3-5.

[0021] When sampling brine from the discharge well, the sampling interval is 0.5 to 1 hour, and the sampling cycle is 24 hours, to allow sufficient time for nitrogen to rise.

[0022] After the height of the upper edge of the connecting channel is determined and the injection and production wells are completed, a gas-water interface detector is run into the injection and production tubing, and natural gas is injected through the injection and production tubing to allow natural gas to enter the injection well. The gas-water interface detector is used to monitor the gas-water interface position of natural gas and brine in real time to ensure that the real-time monitored gas-water interface position is above L1 to ensure gas injection safety.

[0023] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining the upper edge of a connected salt cavern channel, characterized in that: Includes the following steps: Step 1: Perform sonar cavity probing on the two cavities of the connected well, designating the well with the greater cavity bottom depth as the gas injection well and the well with the smaller cavity bottom depth as the brine discharge well; Step 2: Inject liquid to dissolve the salt ore into the gas injection well and the brine discharge well to form brine; Step 3: Run a test string into the injection well until the test string contacts the bottom of the injection well cavity, and record the depth L of the test string. Step 4: Inject nitrogen into the test string that was lowered in Step 3, so that the gas enters the injection well and seals the annulus between the injection well and the test string. Step 5: Based on Step 4, drain the brine from the brine well and observe whether there are air bubbles in the brine. If there are no air bubbles, it proves that the upper edge of the channel connecting the gas injection well and the brine drain well is below the bottom of the test string. If there are air bubbles, it proves that the upper edge of the channel connecting the gas injection well and the brine drain well is above the test string. Step Six: When the brine discharged from the brine well contains air bubbles, the test string should be pulled up and the operations of Steps Four and Five should be repeated until the brine discharged from the brine well does not contain air bubbles. Record the position L1 of the bottom of the test string at this time, and then pull out the test string to remove it from the gas injection well. Step 7: After the injection and production of the gas injection well is completed, a gas-water interface detector is installed in the injection and production tubing, and natural gas is injected through the injection and production tubing to allow natural gas to enter the gas injection well. The gas-water interface detector is used to monitor the gas-water interface position of natural gas and brine in real time to ensure that the real-time monitored gas-water interface position is above L1 to ensure gas injection safety.

2. The method for determining the upper edge of a connected salt cavern channel according to claim 1, characterized in that: In step four, the pressure of nitrogen injected into the test column is X MPa greater than the liquid column pressure at depth L, where X is a constant ranging from 0.1 to 5.

3. The method for determining the upper edge of a connected salt cavern channel according to claim 2, characterized in that: The formula for calculating the nitrogen injection pressure is P=0.0098*ρ*L+X, where: P is the nitrogen injection pressure; ρ is the brine density; and L is the depth of the tubing.

4. The method for determining the upper edge of a connected salt cavern channel according to claim 3, characterized in that: The formula for calculating the nitrogen injection volume is Q=a*V*P / P0, where: V is the volume of the tubing; P0 is the standard atmospheric pressure; and a is a constant with a value range of 3-5.

5. The method for determining the upper edge of a connected salt cavern channel according to claim 1, characterized in that: The liquid in step two is either water or unsaturated brine.

6. The method for determining the upper edge of a connected salt cavern channel according to claim 1, characterized in that: The formula for calculating the bottom position L1 of the test tube is L1=LY*n, where n is the number of times the test tube is lifted, and Y is the height of lifting the test tube. The distance of lifting the test tube is the same each time.

7. The method for determining the upper edge of a connected salt cavern channel according to claim 1, characterized in that: In step five, samples are periodically taken from the brine discharge pipeline of the brine discharge well. The presence of air bubbles in the brine sample is used to determine whether the brine in the brine discharge well contains air bubbles.

8. The method for determining the upper edge of a connected salt cavern channel according to claim 7, characterized in that: When the sample brine contains air bubbles, a gas analyzer is used to detect whether the gas contained in the air bubbles is nitrogen.

9. The method for determining the upper edge of a connected salt cavern channel according to claim 7, characterized in that: The brine sampling interval is 0.5 to 1 hour, and the sampling cycle is 24 hours.

10. The method for determining the upper edge of a connected salt cavern channel according to claim 1, characterized in that: The data obtained from the sonar cavity measurement in step one includes the cavity morphology and volume, cavity top depth and cavity bottom depth of the gas injection well and brine discharge well.

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