A method for plugging a depleted well for carbon sequestration

Abstract

The application discloses a carbon sequestration abandoned well plugging method, which comprises the following steps: closing the open hole or the perforated section to form a first plug surface, the position of the first plug surface being higher than the casing shoe of the technical casing; injecting cement on the first plug surface to form a second plug surface; injecting a suspending agent on the second plug surface to form a suspending agent layer, wherein the suspending agent comprises barite and Pb(OH)2; injecting cement on the suspending agent layer to form a third plug surface, the position of the third plug surface being higher than the cement return depth of the production casing; lowering a light oil pipe to the upper part of the wellbore; and injecting an anticorrosive liquid on the third plug surface. The carbon sequestration abandoned well plugging method can solve the problem of carbon sequestration abandoned well, can solve the problem of using a conventional cement plug or a mechanical well plugging process to plugging the CCUS abandoned well, and can guarantee long-term effective sealing of the wellbore and solve the problem of serious safety hazards.

Description

Technical Field

[0001] This invention relates to the field of abandoned well sealing technology, and more particularly to a method for sealing abandoned wells containing carbon deposits. Background Technology

[0002] CCUS pilot testing aims to achieve the dual goals of carbon sequestration and significantly improving oilfield recovery. However, CO2 moisture is extremely corrosive to ordinary alloy steel and has a strong penetrating ability into micro-cracks. Even if abandoned carbon sequestration wells employ the highest-standard sealing technology currently available, the "termite effect" can still lead to seal failure, creating long-term safety hazards.

[0003] Currently, there is no effective method for sealing abandoned CCUS wells. The highest standard for conventional abandoned well sealing is the "Operation Procedure for Sealing Abandoned Wells in Gas Storage Facilities" and the "Technical Specification for Permanent Sealing of Natural Gas Wells". The main methods used are conventional plugs such as cement plugs and bridge plugs, plus heavy crystal plugs and corrosion inhibitors for sealing.

[0004] Existing technology discloses a safe, environmentally friendly, and pressure-relief well sealing device, which sets up four rubber sleeves with different hardnesses and arranges them from top to bottom in order of decreasing hardness. The advantage of this structure is that when the rubber sleeves are set, only the bottommost rubber sleeve D with the lowest hardness needs to be set, so the required setting pressure is very small. Large equipment such as work vehicles, pump trucks, and water tankers are not required during setting, which greatly reduces the operating cost.

[0005] Existing technologies also disclose methods for plugging permanently abandoned oil, gas, and water wells. For the lower perforated layers of the producing formation, direct cement slurry injection is used for plugging; for the uppermost perforated layers, ultrafine cement slurry is injected using a cement retainer. For plugging the caprock above the producing formation, the following considerations must be taken into account: if there is a continuous high-quality cementing section of more than 20m below the caprock and above the oil cap, or a 200m section of qualified cementing quality between the oil cap and the top of the caprock, then direct cement slurry injection is used to plug the caprock location. Otherwise, a bridge plug is first installed 15-20m below the caprock location, followed by milling 25m of casing and then open-hole cement slurry injection for plugging.

[0006] However, if the above conventional well sealing process is used to seal the abandoned wells in the CCUS test, CO2 will cause pitting and cratering of the well casing, cement or mechanical plug, which may lead to failure of the high-pressure buried seal and cause major environmental leakage and other safety hazards.

[0007] Therefore, a method is needed to eliminate the safety hazards of abandoned wellbores in CCUS tests and achieve long-term safe well sealing. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a method for sealing abandoned wells with carbon sequestration (CCUS). This method is used to eliminate safety hazards in abandoned wells with CCUS and achieve long-term safe well sealing. It is applicable to CO2 flooding in oil and gas fields and the safe sealing of abandoned CCUS wells, thereby preventing wellbore corrosion and CO2 gas leakage that could cause production losses and personnel casualties.

[0009] Based on this, the following technical solution is adopted:

[0010] The present invention discloses a method for sealing abandoned carbon burial wells, the method comprising:

[0011] The exposed hole or perforation section is sealed by resin and cement injection and mechanical plugging to form the first plug surface, which is positioned higher than the casing shoe of the technical casing.

[0012] The first plug surface is sealed with cement to form the second plug surface;

[0013] A suspension layer is formed by injecting a suspension agent into the second stopper surface, wherein the suspension agent contains barite and Pb(OH)2;

[0014] Cement is injected onto the suspension layer to form a third plug surface, which is positioned higher than the cement return depth of the production casing.

[0015] A smooth oil pipe is installed at the top of the wellbore, and corrosion inhibitor is injected into the third plug surface.

[0016] Furthermore, the suspension also includes a dispersant and water.

[0017] Furthermore, the components of the suspension are as follows by mass percentage: barite 30-50%, Pb(OH)2 10%-20%, dispersant 1-2%, and the balance is water.

[0018] Furthermore, the preparation of the suspension comprises the following steps:

[0019] After adding barite powder to water, Pb(OH)2 powder is added, and finally a dispersant is added and stirred evenly to form a suspension.

[0020] Furthermore, the position of the first plug surface is 30m higher than the casing shoe of the technical casing.

[0021] Furthermore, the amount of resin and cement added during the resin injection and cement sealing process:

[0022]

[0023] Where r1 is the design sealing radius, r2 is the oil layer casing radius, h1 is the sealing layer thickness, and h2 is the plugging agent thickness inside the wellbore. Porosity.

[0024] Furthermore, the resin contains phenolic or epoxy resins that are resistant to CO2 corrosion, and the cement contains corrosion-resistant cement.

[0025] Furthermore, the resin and cement are mixed at a weight ratio of 1:2.

[0026] Furthermore, the main component of the dispersant is sodium hexametaphosphate.

[0027] Furthermore, the corrosion inhibitor is a CO2-resistant corrosion inhibitor.

[0028] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0029] The sealing method for abandoned carbon burial wells provided by this invention can solve the problem that the long-term "termite-eating effect" of CO2 may lead to the failure of the high-pressure burial seal, resulting in a major environmental leakage safety hazard.

[0030] This invention employs a bottom-up well-sealing process, sequentially sealing the producing formation and the wellbore. First, resin and cement are used to seal the open hole or perforated section, with the plug surface positioned 30m above the technical casing shoe. The upper end is reinforced and sealed with a CO2-resistant bridge plug. Then, Pb(OH)2 + barite is selected as a long-lasting and safe well-sealing agent to achieve self-sealing repair of the leaking section, blocking and delaying the "termite-eating effect" of CO2 on the wellbore. Combined with the upper cement plug seal, a smooth tubing is installed at the top of the wellbore, and corrosion inhibitor is injected, achieving quadruple well-sealing safety protection.

[0031] The advantages of the method for sealing abandoned carbon burial wells of the present invention are as follows: (1) The resin + cement sealing agent used in the present invention is a CO2 corrosion resistant material. The resin is mainly phenolic or epoxy resin, and the cement is CO2 erosion resistant cement. The weight ratio of resin to cement is 1:2, and the amount of resin added is Q = π(r1 2 -r2 2 )h1φ+πr2 2h2r1 is the design sealing radius, r2 is the oil layer casing radius, h1 is the sealing layer thickness, h2 is the thickness of the plugging agent in the wellbore, and φ is the porosity. The plugging agent can withstand pressure of more than 35MPa after curing; (2) The bridge plug used is a CO2 corrosion resistant bridge plug, the main material is 13Cr, and the sealing material is CO2 corrosion resistant rubber; (3) Based on the reaction of Pb(OH)2 with infiltrated CO2 to generate PbCO3 precipitate, barite and PbCO3 are mixed with corrosion products through self-crystallization under high temperature and high pressure conditions to achieve self-sealing repair of corrosion in the leakage section and block and delay the "termite effect" of CO2 on the wellbore; (4) From bottom to top, the following processes are used: corrosion resistant resin + cement plug, corrosion resistant bridge plug, self-repair and blockage of barite and PbCO3, and corrosion resistant cement plug + upper-end injection of corrosion inhibitor to achieve quadruple well sealing safety protection. It can fundamentally guarantee the long-term safety and effectiveness of sealing abandoned carbon deposit wells.

[0032] Compared with existing technologies, the sealing method of this invention has the advantages of simple construction steps, high success rate, and high process safety; after well sealing, the CO2 gas permeability is less than 7.34×10⁻⁶. -3 mD; The sealing method of the present invention can achieve long-term effective sealing of abandoned wells, meeting the needs of sealing abandoned wells in CCUS tests. Attached Figure Description

[0033] 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.

[0034] Figure 1 This is a schematic diagram illustrating the sealing effect of an abandoned well in a CCUS test according to an embodiment of the present invention;

[0035] Figure 2 This is a flowchart illustrating a method for sealing abandoned wells according to an embodiment of the present invention.

[0036] [List of Labels in the Attached Image]

[0037] 2. Cement return depth, 3. Casing shoe of technical casing, 4. Casing shoe of oil casing, 5. Construction pipe column, 6. First cement plug, 7. Suspension layer, 8. Second cement plug, 9. Mechanical plug, 10. Cement plug / resin plug. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0039] like Figure 1 The diagram shown illustrates the sealing effect of abandoned wells during the CCUS test.

[0040] First, seal the open hole or perforated section using resin or cement injection combined with mechanical sealing. The sealing surface should be higher than the casing shoe by 3. The amount of resin and cement added... r1 is the design sealing radius, r2 is the oil layer casing radius, h1 is the sealing layer thickness, and h2 is the plugging agent thickness inside the wellbore. Porosity. Then, a mechanical plugging method is used for reinforcement and sealing. Based on this, cement is injected for further sealing. Next, a suspension formed by mixing barite + Pb(OH)2 powder and a small amount of dispersant is injected into the wellbore. The suspension layer thickness is ≥300 μm. Finally, cement is injected above this suspension layer for reinforcement and sealing to form the first cement plug 6. The thickness of the first cement plug 6 should exceed 300 μm, and the plug surface should be controlled above the cement return height of the production casing. A smooth tubing is installed at the top of the wellbore, and corrosion inhibitor is injected to fundamentally prevent wellbore corrosion and CO2 upflow along the wellbore.

[0041] like Figure 2 The method for sealing abandoned carbon burial wells shown in the embodiment of the present invention employs a bottom-up sealing process, sequentially sealing the producing layer and the well casing.

[0042] The method includes the following steps:

[0043] Step S101: First, resin and cement are injected to form a cement plug / resin plug 10. Then, a mechanical plug 9 is formed on top of the cement plug / resin plug by mechanical plugging to seal the open hole or perforation section. The mechanical plug has a first plug surface, which is positioned higher than the casing shoe 3 of the technical casing.

[0044] Step S102: Cement is injected into the first plug surface to form a second cement plug 8, which has a second plug surface;

[0045] Step S103: Inject a suspension agent into the second plug surface to form a suspension agent layer 7, wherein the suspension agent contains barite and Pb(OH)2;

[0046] Step S104: Cement is injected onto the suspension layer to form a first cement plug 6. The first cement plug 6 has a third plug surface, and the position of the third plug surface is higher than the cement return depth 2 of the production casing.

[0047] Step S105: Lower the oil tubing (i.e., construction string 5) into the upper part of the wellbore and inject corrosion inhibitor on the third plug surface.

[0048] The suspension contains barite, Pb(OH)₂, a dispersant, and water. Barite is an inorganic compound, mainly composed of BaSO₄, and consists of white, thick, plate-like crystals with a density of 4.3 g / cm³. 3It is non-toxic. Pb(OH)₂ is an inorganic compound with a density of 7.59 g / cm³. 3 It is insoluble in water, toxic, a white amorphous powder or solid, tasteless and odorless, and decomposes at 145℃.

[0049] The components of the suspension, by mass percentage, are: barite 30-50%, Pb(OH)2 10%-20%, dispersant 1-2%, and the balance is water.

[0050] The preparation of a suspension includes the following steps:

[0051] After adding barite powder to water, Pb(OH)2 powder is added, and finally a dispersant is added and stirred evenly to form a suspension.

[0052] The first plug surface is positioned 30m above the casing shoe of the technical casing.

[0053] The amount of resin and cement added during the resin and cement sealing process:

[0054]

[0055] Where r1 is the design sealing radius, r2 is the oil layer casing radius, h1 is the sealing layer thickness, and h2 is the plugging agent thickness inside the wellbore. Porosity.

[0056] The resin contains phenolic or epoxy resins that are resistant to CO2 corrosion, and the cement contains corrosion-resistant cement.

[0057] The resin and cement are mixed at a weight ratio of 1:2.

[0058] The main dispersant is sodium hexametaphosphate, a white crystalline powder, odorless.

[0059] The corrosion inhibitor is a CO2-resistant corrosion inhibitor for downhole use in oil and gas wells (specifically, it uses the salt-resistant corrosion and scale inhibitor for downhole use in oil and gas wells disclosed in patent application ZL201310597223.6, the content of which is hereby incorporated into this invention), a brownish-red liquid with a density of 0.9 g / cm³. 3 Chemically pure.

[0060] All embodiments are based on indoor physical model experiments conducted with reference to field well examples.

[0061] Field well case reference: Abandoned oil well (reference) Figure 1The well has been drilled to a depth of 4003m, with open-hole completion. The open-hole section is 15m long, and the cementing quality is consistently excellent for more than 20m. The technical casing shoe 3 is located at 2552.38m, the oil casing shoe 4 at 3986.15m, and the oil casing cement return depth is 377.0m. Gas injection is about to be implemented in this fault block at a pressure of 29MPa, with a maximum downhole temperature of 135℃. To prevent gas from leaking from the producing formation to the surface, well sealing is required.

[0062] The following Examples 1-4 simulate the formation of the suspension in step S103 and the reaction of the suspension with CO2 under well pressure using laboratory conditions.

[0063] Example 1 :

[0064] Indoor physical model experiments were conducted using a high-temperature, high-pressure reactor. First, 500 mL of water was added to a beaker, followed by 30 wt% BaSO4 powder, then 10 wt% Pb(OH)2 powder, and finally 1 wt% dispersant. The mixture was stirred until homogeneous, forming a BaSO4 + Pb(OH)2 suspension. This suspension was then added to the reactor to create a sealed environment. CO2 gas was introduced, and the pressure was controlled at 29 MPa and the temperature at 135 °C. After a full reaction of 4 hours, the gas source was shut off, the reactor was opened, and the interior was observed to have completely formed a BaSO4 + PbCO3 solid. The BaSO4 + PbCO3 solid was removed, and its hardness and gas permeability were measured. The hardness of the BaSO4 + PbCO3 solid was 3.5, and the CO2 gas permeability was 7.34 × 10⁻⁶. -3 mD can meet the long-term safe well sealing requirements on site.

[0065] Example 2 :

[0066] Indoor physical model experiments were conducted using a high-temperature, high-pressure reactor. First, 500 mL of water was added to a beaker, followed by 30 wt% BaSO4 powder, then 20 wt% Pb(OH)2 powder, and finally 1 wt% dispersant. The mixture was stirred until homogeneous, forming a BaSO4 + Pb(OH)2 suspension. This suspension was then added to the reactor to create a sealed environment. CO2 gas was introduced, and the pressure was controlled at 29 MPa and the temperature at 135 °C. After a full reaction of 4 hours, the gas source was shut off, the reactor was opened, and the interior was observed to have completely formed a BaSO4 + PbCO3 solid. The BaSO4 + PbCO3 solid was removed, and its hardness and gas permeability were measured. The hardness of the BaSO4 + PbCO3 solid was 3.65, and the CO2 gas permeability was 5.95 × 10⁻⁶. -3 mD can meet the long-term safe well sealing requirements on site.

[0067] Example 3 :

[0068] Indoor physical model experiments were conducted using a high-temperature, high-pressure reactor. First, 500 mL of water was added to a beaker, followed by 40 wt% BaSO4 powder, then 10 wt% Pb(OH)2 powder, and finally 1 wt% dispersant. The mixture was stirred thoroughly to form a BaSO4 + Pb(OH)2 suspension. This suspension was then added to the reactor to create a sealed environment. CO2 gas was introduced, and the pressure was controlled at 29 MPa and the temperature at 135 °C. After a full reaction of 4 hours, the gas source was shut off, the reactor was opened, and the interior was observed to have completely formed a BaSO4 + PbCO3 solid. The BaSO4 + PbCO3 solid was removed, and its hardness and gas permeability were measured. The hardness of the BaSO4 + PbCO3 solid was 3.7, and the CO2 gas permeability was 5.62 × 10⁻⁶. -3 mD can meet the long-term safe well sealing requirements on site.

[0069] It should be noted that the components or steps in the above embodiments can be interchanged, substituted, added, or deleted. Therefore, the combinations formed by these reasonable permutations and transformations should also fall within the protection scope of this invention, and the protection scope of this invention should not be limited to the above embodiments.

[0070] The above are exemplary embodiments disclosed in this invention. The order of the disclosed embodiments is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0071] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for sealing abandoned wells used for carbon burial, characterized in that, The method includes: The open hole or perforation section is sealed to form a first plug surface, which is positioned higher than the casing shoe of the technical casing. The open hole or perforation section is sealed by means of resin injection and cement sealing, and mechanical plugging to form the first plug surface. The resin contains phenolic or epoxy resin that is resistant to CO2 corrosion. The first plug surface is sealed with cement to form the second plug surface; A suspension is injected into the second stopper surface to form a suspension layer, wherein the components of the suspension are as follows by mass percentage: barite 30-50%, Pb(OH)2 10%-20%, dispersant 1-2%, and the balance is water; wherein the main component of the dispersant is sodium hexametaphosphate. Cement is injected onto the suspension layer to form a third plug surface, which is positioned higher than the cement return depth of the production casing. A smooth oil tubing is installed at the top of the wellbore, and a corrosion inhibitor is injected into the third plug surface; the corrosion inhibitor is a CO2-resistant corrosion inhibitor. Cement includes corrosion-resistant cement.

2. The method for sealing abandoned wells for carbon burial according to claim 1, characterized in that, The preparation of the suspension includes the following steps: After adding barite powder to water, Pb(OH)2 powder is added, and finally a dispersant is added and stirred evenly to form a suspension.

3. The method for sealing abandoned wells for carbon burial according to claim 1, characterized in that, The first plug surface is positioned 30m above the casing shoe of the technical casing.

4. The method for sealing abandoned wells for carbon burial according to claim 3, characterized in that, The amount of resin and cement added during the resin and cement sealing process: Q=π(r1 2 –r2 2 )h1φ+πr2 2 h2, Where r1 is the design sealing radius, r2 is the oil layer casing radius, h1 is the sealing layer thickness, h2 is the plugging agent thickness in the wellbore, and φ is the porosity.

5. The method for sealing abandoned carbon burial wells according to claim 4, characterized in that, The resin and cement are mixed at a weight ratio of 1:2.

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