A well sealing method that utilizes salt rock creep to form a barrier in salt cavern carbon sequestration wells.

Abstract

This invention discloses a well sealing method for utilizing salt rock creep to form a barrier in salt cavern carbon sequestration wells, comprising the following steps: S1: Selecting a target salt cavern carbon sequestration well; S2: Lowering a bottom bridge plug into the bottom of the wellbore; S3: Lowering a casing milling tool to the salt rock layer, cutting off the casing above the bottom bridge plug, and removing the annular cement sheath in the salt rock layer to form an enlarged section; S4: Circulating drilling fluid to remove casing and cement sheath debris from the wellbore; S5: Measuring the diameter of the enlarged section; S6: Backfilling the enlarged section with broken salt rock and compacting it to form a broken salt rock backfill section; S7: Lowering a top bridge plug above the broken salt rock backfill section to seal it; S8: Injecting cement sealing material above the top bridge plug to form a cement plug. This invention can utilize the creep behavior of the salt rock in the broken salt rock backfill section under high temperature and high pressure conditions to repair the backfill section, restore the original porosity and permeability of the caprock, and re-establish a natural salt barrier.

Description

Technical Field

[0001] This invention relates to the field of wellbore sealing technology, and in particular to a well sealing method that utilizes salt rock creep to form a barrier in a salt cavern carbonized well. Background Technology

[0002] Chinese rock salt deposits range from tens to five thousand meters underground, with thicknesses varying from tens to hundreds of meters. Long-term water-soluble extraction has created abundant salt cavern resources. Salt caverns, with their low permeability, chemical stability, and non-reaction with carbon dioxide, are ideal sites for carbon sequestration. Salt cavern carbon sequestration is a technology that uses wellbores to transport liquefied carbon dioxide to underground salt caverns for permanent storage. Due to the long storage time, there is a risk of carbon dioxide leakage along the wellbore; therefore, a well-sealing method that maintains the wellbore's long-term seal is crucial.

[0003] For permanent carbon dioxide sequestration, the conventional well sealing method is the injection plugging method, which involves injecting sealing material (usually cement) into the target well section, allowing it to penetrate the formation, damaged casing, or the annulus outside the casing to form a seal, and controlling the seal within the well to be in the designed position. Due to the extremely strong creep capacity of salt rock, continuous compression of the wellbore can cause wellbore damage, leading to seal failure. Furthermore, if the salt cavern contains water, carbon dioxide dissolves in the water, creating an acidic environment that continuously corrodes the casing and cement sheath, posing a risk of leakage. Carbon dioxide leakage caused by wellbore seal failure severely restricts the large-scale development of carbon sequestration in salt caverns. Therefore, how to achieve a permanent seal of the wellbore when sequestering carbon dioxide in salt caverns is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a well sealing method that utilizes salt rock creep to form a barrier in salt cavern carbon sequestration wells.

[0005] The technical solution of the present invention is as follows:

[0006] A well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbon sequestration well includes the following steps:

[0007] S1: Select a wellbore suitable for utilizing the salt rock creep to form a barrier as the target salt cavern carbon fixation well, and obtain the initial water content of the salt rock from the core library collected during drilling;

[0008] S2: Insert a bottom bridge plug at the bottom of the wellbore to seal off the carbon dioxide already injected into the salt cavern;

[0009] S3: Lower the casing forging and milling tool to the salt rock layer section, cut off the casing above the bottom bridge plug, and remove the annular cement ring in the salt rock layer section to form an enlarged section;

[0010] S4: Circulate drilling fluid to remove casing and cement sheath debris from the wellbore, then replace the drilling fluid in the wellbore with a large amount of clean water, and finally replace the fluid in the wellbore with gas;

[0011] S5: Lower the borehole caliper measuring tool to measure the diameter of the enlarged section;

[0012] S6: Run a coiled tubing with a bottom drain outlet into the well. Based on the diameter measurement of the enlarged section, backfill the fractured salt rock from the outer annulus of the tubing into the enlarged section. After backfilling, replenish water to the fractured salt rock through the coiled tubing drain outlet. The salt rock in the backfilled section undergoes creep under the high temperature and high pressure conditions of the formation. After water replenishment, the creep rate increases, forming a natural salt barrier.

[0013] S7: Insert a top bridge plug above the fractured salt rock backfill section to seal the fractured salt rock backfill section;

[0014] S8: Inject cement sealing material above the top bridge plug to form a cement plug.

[0015] Preferably, in step S1, the wellbore suitable for forming a barrier by utilizing salt rock creep refers to a wellbore that meets the requirement that the thickness of the top of the salt cavern is not less than 80m.

[0016] Preferably, in step S2, the bottom bridge plug is installed at a wellbore position at least 30m above the bottom of the well.

[0017] Preferably, in step S3, the height of the eye-expanding segment is greater than 50m.

[0018] Preferably, in step S4, weighted drilling fluid is used to remove casing and cement sheath debris from the wellbore.

[0019] Preferably, in step S6, the volume of the backfilled broken salt rock is calculated using the following formula:

[0020]

[0021] In the formula: V is the volume of the backfilled broken salt rock, in meters. 3 n is the number of segments in the eye-expanding segment; r i Let h be the radius of the i-th segment of the enlarged wellbore, in meters. i Let the height of the i-th segment of the enlarged borehole be m;

[0022] The volume of water replenished to the fractured salt rock is calculated using the following formula:

[0023]

[0024] In the formula: W is the water replenishment volume, m 3 W n Water content of salt rock recorded during drilling and coring, %; Wo The moisture content of the backfilled broken salt rock, measured on-site, is %.

[0025] Preferably, in step S8, the cement sealing material is injected using the circulating injection method.

[0026] Preferably, in step S8, the height of the cement plug is greater than 30m.

[0027] Preferably, the method also includes the step of installing a carbon dioxide monitor at the wellhead to monitor for any carbon dioxide leakage from the wellbore.

[0028] Preferably, the carbon dioxide monitor is monitored at an interval of no less than once every 12 hours.

[0029] The beneficial effects of this invention are:

[0030] (1) The present invention backfills the broken salt rock to the bottom of the well and uses the creep behavior of the original salt rock section under high temperature and high pressure to continuously squeeze the backfilled broken salt rock, reduce the porosity and permeability of the backfill section until it is consistent with the original salt rock section, and re-establish the natural salt barrier.

[0031] (2) This invention utilizes the natural salt barrier formed by the creep of salt rock, which not only ensures the permanent storage of carbon dioxide but also avoids the problem of carbon dioxide corrosion and solves the problem of carbon dioxide leakage along the wellbore. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic flowchart of the well sealing method of the present invention, which utilizes salt rock creep to form a barrier in a salt cavern carbon sequestration well.

[0034] Numbers in the diagram: 1-Casing; 2-Cement ring; 3-Salt rock section; 4-Bottom bridge plug; 5-Enlarged section; 6-Fractured salt rock; 7-Top bridge plug; 8-Cement plug; 9-Carbon dioxide monitor. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0036] like Figure 1 As shown, this invention provides a well sealing method for utilizing salt rock creep to form a barrier in salt cavern carbon sequestration wells, comprising the following steps:

[0037] S1: Select a wellbore suitable for utilizing the salt rock creep to form a barrier as the target salt cavern carbon fixation well, and obtain the initial water content of the salt rock from the core library collected during drilling.

[0038] In one specific embodiment, the wellbore suitable for forming a barrier by utilizing salt rock creep refers to a wellbore that meets the requirement that the thickness of the top of the salt cavern is not less than 80m.

[0039] S2: Insert bottom bridge plug 4 into the bottom of wellbore 1 to seal the carbon dioxide already injected into the salt cavern.

[0040] In one specific embodiment, the bottom bridge plug 4 is installed at a wellbore location at least 30m above the bottom of the well.

[0041] S3: Lower the casing forging and milling tool to the salt rock layer section 3, cut off the casing 1 above the bottom bridge plug 4, and remove the annular cement ring in the salt rock layer section to form the enlarged eye section 5.

[0042] In one specific embodiment, the height of the eye-expanding segment 5 is greater than 50m.

[0043] S4: Circulate drilling fluid to remove casing and cement sheath debris from the wellbore, then replace the drilling fluid in the wellbore with a large amount of clean water, and finally replace the fluid in the wellbore with gas.

[0044] In one specific embodiment, a weighted drilling fluid is used to remove casing and cement sheath debris from the wellbore. Optionally, the weighted drilling fluid is a mixture of barite and bentonite. In this embodiment, using a weighted drilling fluid to remove casing and cement sheath debris from the wellbore can suppress the creep process of the surrounding exposed rock salt layer during borehole enlargement.

[0045] S5: Lower the wellbore measuring tool to measure the diameter of the enlarged section 5.

[0046] In one specific embodiment, a wellbore measurement tool is lowered using a cable logging method.

[0047] S6: Run a coiled tubing with a bottom drain outlet into the well. Based on the diameter measurement of the enlarged section 5, backfill the fractured salt rock 6 from the outer annulus of the tubing into the enlarged section 5. After backfilling, replenish water to the fractured salt rock through the coiled tubing drain outlet. The salt rock in the backfilled section undergoes creep under the high temperature and high pressure conditions of the formation. After water replenishment, the creep rate increases, forming a natural salt barrier.

[0048] In one specific embodiment, the volume of backfilled fractured salt rock is calculated using the following formula:

[0049]

[0050] In the formula: V is the volume of the backfilled broken salt rock, in meters. 3 n is the number of segments in the eye-expanding segment; r i Let h be the radius of the i-th segment of the enlarged wellbore, in meters. i Let the height of the i-th segment of the enlarged borehole be m;

[0051] The volume of water replenished to the fractured salt rock is calculated using the following formula:

[0052]

[0053] In the formula: W is the water replenishment volume, m 3 W n Water content of salt rock recorded during drilling and coring, %; W o The moisture content of the backfilled broken salt rock, measured on-site, is %.

[0054] In one specific embodiment, the fractured salt rock is salt rock that is returned to the surface during drilling and collected and stored.

[0055] S7: Insert a top bridge plug 7 above the broken salt rock backfill section to seal the broken salt rock backfill section.

[0056] S8: Inject cement sealing material above the top bridge plug 7 to form cement plug 8.

[0057] In one specific embodiment, the cement sealing material is injected using a circulating injection method, and the height of the cement plug 8 is greater than 30m.

[0058] In one specific embodiment, the well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbon sequestration well according to the present invention further includes the step of installing a carbon dioxide monitor 9 at the wellhead to monitor whether carbon dioxide is leaking from the wellbore. Optionally, the monitoring interval of the carbon dioxide monitor 9 is not less than once every 12 hours.

[0059] In a specific embodiment, taking a 3000-meter well as an example, using the well-sealing method described in this invention—which utilizes salt rock creep to form a barrier in a salt cavern carbon sequestration well—the backfilled fractured salt rock can be restored to its original stress state and its original rock salt permeability after about one year. The backfilled well section is repaired, and a natural salt barrier is re-established.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A well sealing method for utilizing salt rock creep to form a barrier in salt cavern carbon sequestration wells, characterized in that, Includes the following steps: S1: Select a wellbore suitable for utilizing the salt rock creep to form a barrier as the target salt cavern carbon fixation well, and obtain the initial water content of the salt rock from the core library collected during drilling; S2: Insert a bottom bridge plug at the bottom of the wellbore to seal off the carbon dioxide already injected into the salt cavern; S3: Lower the casing forging and milling tool to the salt rock layer section, cut off the casing above the bottom bridge plug, and remove the annular cement ring in the salt rock layer section to form an enlarged eye section; S4: Circulate drilling fluid to remove casing and cement sheath debris from the wellbore, then replace the drilling fluid in the wellbore with a large amount of clean water, and finally replace the fluid in the wellbore with gas; S5: Lower the borehole caliper measuring tool to measure the diameter of the enlarged section; S6: Run a coiled tubing with a bottom drain outlet into the well. Based on the diameter measurement of the enlarged section, backfill the fractured salt rock from the outer annulus of the tubing into the enlarged section. After backfilling, replenish water to the fractured salt rock through the coiled tubing drain outlet. The salt rock in the backfilled section undergoes creep under the high temperature and high pressure conditions of the formation. After water replenishment, the creep rate increases, forming a natural salt barrier. S7: Insert a top bridge plug above the fractured salt rock backfill section to seal the fractured salt rock backfill section; S8: Inject cement sealing material above the top bridge plug to form a cement plug.

2. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbon sequestration well according to claim 1, characterized in that, In step S1, the wellbore suitable for forming a barrier by utilizing salt rock creep refers to a wellbore that meets the requirement that the thickness of the top of the salt cavern is not less than 80m.

3. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbonization well according to claim 1, characterized in that, In step S2, the bottom bridge plug is installed at a wellbore position at least 30m above the bottom of the well.

4. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbon sequestration well according to claim 1, characterized in that, In step S3, the height of the eye-expanding segment is greater than 50m.

5. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbon sequestration well according to claim 1, characterized in that, In step S4, heavy-duty drilling fluid is used to remove casing and cement sheath debris from the wellbore.

6. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbonization well according to claim 1, characterized in that, In step S6, the volume of backfilled broken salt rock is calculated using the following formula: In the formula: V is the volume of the backfilled broken salt rock, in meters. 3 n is the number of segments in the eye-expanding segment; r i Let h be the radius of the i-th segment of the enlarged wellbore, in meters. i Let the height of the i-th segment of the enlarged borehole be m; The volume of water replenished to the fractured salt rock is calculated using the following formula: In the formula: W is the water replenishment volume, m 3 W n Water content of salt rock recorded during drilling and coring, %; W o The moisture content of the backfilled broken salt rock, measured on-site, is %.

7. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbonization well according to claim 1, characterized in that, In step S8, the cement sealing material is injected using the circulating injection method.

8. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbon sequestration well according to claim 1, characterized in that, In step S8, the height of the cement plug is greater than 30m.

9. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbonization well according to any one of claims 1-8, characterized in that, It also includes the step of installing a carbon dioxide monitor at the wellhead to monitor for any carbon dioxide leakage from the wellbore.

10. The well sealing method for utilizing salt rock creep to form a barrier in a salt cavern carbonization well according to claim 9, characterized in that, The monitoring interval of the carbon dioxide monitor shall not be less than once every 12 hours.

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