Method for preventing casing deformation in gypsolith intervals and device therefor

Abstract

The present application relates to a method for preventing casing deformation in gypsolith intervals, comprising obtaining a reamed section of a gypsolith interval; obtaining a first well section below the reamed section, a second well section above the reamed section, a first annulus, a second annulus, and a reamed annulus; providing a first cementing stage collar and a first packer and a second cementing stage collar and a second packer; injecting cement slurry into the first annulus to perform primary cementing; isolating the cement slurry in the first annulus from the reamed annulus by the first packer; filling the reamed annulus with an equal-pressure medium by the first cementing stage collar; isolating the equal-pressure medium from the second annulus by the second packer; injecting cement slurry into the second annulus to perform secondary cementing by the second cementing stage collar; and allowing the cement slurry to set during the primary and secondary cementing processes. The present application fills the reamed annulus with an equal-pressure medium for isolation and anticorrosion effect to achieve the purpose of preventing casing deformation and corrosion with a small increase in cost and simple and easy-to-operate operation.

Description

Technical Field

[0001] This invention relates to the field of oilfield production technology, and more specifically, to a method and apparatus for preventing casing deformation in gypsum-salt rock formations. Background Technology

[0002] During oilfield drilling, when drilling through gypsum-salt rock formations and bringing them into contact with drilling mud, the gypsum-salt rock undergoes a dissolution and hydration reaction with the water in the drilling mud. This causes volume changes and creates uneven stress, leading to casing deformation. This makes it difficult for injection / production tubing and downhole operations and workover tools to pass through, and in severe cases, it can even render the well unusable. Casing deformation caused by gypsum-salt rock is difficult and costly to repair; therefore, the primary approach is to take preventative measures during drilling, cementing, and completion.

[0003] In their article "Mechanism and Prevention Methods of Casing Deformation in Jingqiu Oilfield" published in *Petroleum Drilling and Production Technology*, Vol. 16, No. 2, 1994, Zhang Xianpu et al. argued that different forms of external extrusion loads significantly affect the degree of damage to the casing. However, regardless of the load form, the problem of the casing's resistance to external extrusion pressure must be addressed. The greater the non-uniformity of the load, the more necessary it is to improve the casing's resistance to crushing. The main methods for preventing casing deformation by increasing the casing's resistance to crushing pressure are as follows:

[0004] (1) Use thickened and high-strength material sleeves

[0005] Increasing the casing wall thickness and using high-strength materials can undoubtedly improve the casing's resistance to crushing to some extent. Calculations show that every 2mm increase in wall thickness can increase crushing resistance by approximately 15%. However, this method relies on rigid support and does not fully utilize the self-supporting capacity of the surrounding rock. While this method is effective under uniform external loads, it cannot effectively address the problem of bearing large, non-uniform loads.

[0006] (2) Using a reinforced sleeve, six 8mm steel bars are symmetrically welded to the outer wall of the sleeve. Calculation results show that the bearing capacity can be increased by 25% to 30%.

[0007] (3) Change the stress state of the strata and improve the self-supporting capacity of the surrounding rock.

[0008] In deformed well sections, a reaming bit is used to drill holes with a larger diameter than those in other sections. Saturated brine, cement, or other media are then injected to allow rock deformation. This allows the surrounding rock to first enter a plastic state, and then the plastic zone expands outward until stress equilibrium is achieved. This method can improve the self-supporting capacity of the surrounding rock to a certain extent, providing joint support for the casing and surrounding rock against external extrusion loads and mitigating the external forces that cause casing deformation.

[0009] (4) Use double-layer combined sleeve

[0010] AMOCO, an American company, successfully used double-layer composite casing in the Suez Gulf to penetrate deep gypsum rock strata, proving it to be a feasible, effective, and reliable method. Theoretical analysis and experimental studies have demonstrated that: (a) the crush resistance of the double-layer composite casing is at least equal to the sum of the crush resistances of each individual casing layer, with an external force transmission coefficient of 0.4–0.6; (b) it can resist large non-uniform external loads. In double-layer composite casing, non-uniform external loads act on the outer casing, causing it to deform. The intermediate cement ring enters a plastic state, making the stress in all directions more uniform, resulting in a more uniform load transmitted to the inner casing than the outer casing, while the casing can withstand a considerable uniform load. Clearly, double-layer composite casing can significantly improve both the overall load-bearing capacity and the ability to resist non-uniform loads. In the field, to save costs, double-layer composite casing can be used only in the deformed sections of the casing.

[0011] In their article "Design and Performance Evaluation of Double-Layer Composite Casing," published in the November 1997 issue of the *Journal of Southwest Petroleum Institute* (Vol. 19, No. 4), Dong Er et al. pointed out that the vast majority of wells in my country experiencing casing damage are concentrated in soft rock formations such as salt rock, mudstone, gypsum rock, and gypsum-salt rock. The article also provided a detailed analysis of the irrationality of current casing string designs in complex formations in my country. Single-layer casing is insufficient to withstand the complex external loads of salt layers. Salt layer casing strings are designed based on overlying formation pressure, and widely use casings such as N80*9.17, P110*9.17, or P110*10.54. However, a large number of casings still deform. The article proposed a design scheme using double-layer composite casing in ultra-high pressure formations, concluding that using locally double-layer composite casing is the optimal solution to address casing deformation in ultra-high pressure formations. For new wells, adopting a double-layer composite casing string structure can ensure that the casing does not deform within its service life. The North China Oilfield has drilled 32 wells using this casing string design scheme. Except for two wells where the casing has undergone significant deformation, all the other wells have successfully withstood the radial ultra-high pressure of the gypsum-salt rock layer.

[0012] Chinese Patent Publication No. CN 111691849 A discloses a process method for solving casing deformation in gypsum-salt formations, including the following steps: After the initial drilling is completed, the wellbore diameter of the gypsum-salt formation and the well section above and below it is expanded using a reamer; the annular volume formed by the well section below the gypsum-salt formation, the well section above the gypsum-salt formation, and the casing of the initial drilling is obtained respectively; the casing string is lowered to the bottom of the well, with the graded collar and expansion packer on the string positioned 20m above the gypsum-salt formation; first-stage cementing is performed: cement slurry of the corresponding annular volume is injected into the space formed by the well section below the gypsum-salt formation and the casing of the initial drilling; second-stage cementing is performed: cement slurry of the corresponding annular volume is injected into the space formed by the well section above the gypsum-salt formation and the casing of the initial drilling; the cement slurry solidifies, leaving the gypsum-salt formation in an unsealed state, thereby releasing the uneven formation stress. This invention transforms uneven stress into uniform stress, eliminating the stress concentration on the casing caused by the uneven cement sheath formed during cementing, thus achieving the effect of preventing casing deformation.

[0013] Dong Er proposed using a local double-layer combined casing in gypsum-salt rock formations for oilfield drilling. Application in the North China Oilfield showed that this method effectively prevents casing deformation. However, it requires increasing the wellbore diameter throughout the entire process from the surface to the gypsum-salt rock formation. The double-layer combined casing increases casing usage, complicates surface assembly, and significantly increases drilling procedures, raising the total drilling cost by 30%-50%. Therefore, Bohai Drilling Engineering Co., Ltd. of China National Petroleum Corporation tested the third method mentioned by Zhang Xianpu et al., namely the process for solving casing deformation in gypsum-salt rock formations (Chinese Patent Publication No. CN111691849A): During conventional drilling, a hole-enlarging, non-cementing method is used to prevent casing deformation in gypsum-salt rock formations, leaving space for deformation. This prevents the gypsum-salt rock from contacting and compressing the casing, thus preventing deformation. This method locally increases the wellbore diameter without increasing casing usage, is simple in process, and only slightly increases drilling procedures, effectively controlling drilling costs. However, the method in Chinese Patent Publication No. CN 111691849 A has two shortcomings: First, after the completion of the oil well, the gypsum-salt rock continues to come into contact with the water (generated by mud degradation) in the enlarged and unconsolidated section, and continues to undergo dissolution and hydration reactions. The uneven stress is still changing, and the risk of casing deformation still exists. Second, the outer wall of the casing comes into contact with the highly mineralized water dissolved in the gypsum-salt rock, causing casing corrosion, which poses a risk of breakage and deformation. Moreover, the corrosion of the outer wall of the casing cannot be prevented and controlled in the well, affecting the life of the well.

[0014] Therefore, it is necessary to find a way to address the risks of casing deformation and external wall corrosion in the gypsum-salt rock formation during oilfield drilling using the enlarged hole, non-cemented well method, in order to better prevent casing deformation. Summary of the Invention

[0015] To address the shortcomings of existing technologies, the present invention aims to provide a method and apparatus for preventing casing deformation in gypsum-salt rock formations. This invention selects a balanced pressure-bearing medium that meets performance requirements for isolation and corrosion prevention, and designs a device to fill this medium into the annulus of the enlarged borehole. This balanced pressure-bearing medium, providing isolation and corrosion prevention, is then filled into the annulus of the uncemented section of the gypsum-salt rock formation, replacing the existing mud. This prevents the gypsum-salt rock from further contacting water and undergoing dissolution and hydration reactions, thus stabilizing the stress in the gypsum-salt rock formation. Consequently, the outer wall of the casing is no longer in contact with the highly mineralized water dissolved in the gypsum-salt rock, preventing corrosion and achieving the goal of preventing casing deformation and corrosion.

[0016] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0017] According to one aspect of the present invention, a method for preventing casing deformation in gypsum-salt rock strata includes:

[0018] Complete drilling and enlarge the borehole in the gypsum-salt rock section to obtain the enlarged section of the gypsum-salt rock section;

[0019] Obtain the first well section below the enlarged section, the second well section above the enlarged section, the first annulus formed outside the casing in the first well section, the second annulus formed outside the casing in the second well section, and the enlarged annulus formed outside the casing in the enlarged section;

[0020] A first cementing stage collar and a first packer outside the casing are provided below the reaming section, and a second cementing stage collar and a second packer outside the casing are provided above the reaming section;

[0021] Inject the corresponding volume of cement slurry into the first annulus for primary cementing;

[0022] The cement slurry in the first annulus is separated from the enlarged annulus by the first packer;

[0023] The first cementing stage ring fills the enlarged annulus with a corresponding volume of balanced pressure-bearing medium.

[0024] The equalizing pressure-bearing medium in the expanded annulus is separated from the second annulus by the second packer;

[0025] Secondary cementing is performed by injecting cement slurry into the second annulus through the second cementing stage clamp; and

[0026] This causes the cement slurry to solidify during the primary and secondary cementing processes.

[0027] In one embodiment of the present invention, the first packer is located 5m below the reaming section, and the second packer is located 5m above the reaming section.

[0028] In one embodiment of the present invention, a first cementing stage collar is connected to a first packer via a first casing stub, and a second cementing stage collar is connected to a second packer via a second casing stub.

[0029] In one embodiment of the invention, the pressure at which the first packer opens and closes is less than the sum of the pressure at which the second packer opens and closes and the pressure of the liquid column between the first and second packers.

[0030] In one embodiment of the present invention, the pressure-balancing medium is selected based on its resistance to high temperature and high pressure, water resistance, adhesion properties, rheological properties, performance in balancing pressure loads, and product price.

[0031] In one embodiment of the present invention, the pressure-balancing medium includes an oil-based gel material.

[0032] In one embodiment of the present invention, the pressure-balancing medium comprises a soap-based thickened hydrocarbon material.

[0033] In one embodiment of the present invention, the pressure-balancing medium is lithium-based grease No. 3.

[0034] In one embodiment of the present invention, the step of separating the cement slurry in the first annulus from the enlarged annulus using a first packer includes:

[0035] Displacement fluid is continuously injected from the wellhead into the casing, pressurized to the opening pressure of the first packer to cause the first packer sleeve to expand, and then the first packer is closed, thereby maintaining the separation of the cement slurry in the first annulus from the enlarged annulus.

[0036] In one embodiment of the present invention, the step of filling the annulus of the enlarged borehole with a corresponding volume of equalizing pressure-bearing medium through a first cementing stage collar includes:

[0037] The opening plug of the first cementing stage collar is inserted into the wellhead. The wellhead is pressurized until the opening plug abuts against the opening sleeve of the first cementing stage collar, thus opening the injection hole of the first cementing stage collar. The equalizing pressure-bearing medium is pumped into the well from the wellhead. Then, the closing plug of the first cementing stage collar is inserted into the wellhead, and displacement fluid is pumped into the well from the wellhead. This causes the closing plug of the first cementing stage collar to push the equalizing pressure-bearing medium downwards, entering the enlarged annulus through the injection hole of the first cementing stage collar, until the closing plug abuts against the closing sleeve of the first cementing stage collar, thus closing the injection hole. In this way, all the equalizing pressure-bearing medium enters the enlarged annulus.

[0038] In one embodiment of the present invention, the step of separating the equalizing pressure-bearing medium within the expanded annulus from the second annulus using a second packer includes:

[0039] Displacement fluid is continuously injected from the wellhead into the casing, pressurizing it to the opening pressure of the second packer to cause the second packer sleeve to expand. Then the second packer is closed to maintain the balanced pressure-bearing medium in the enlarged annulus and separate it from the second annulus.

[0040] In one embodiment of the present invention, the step of injecting cement slurry into the second annulus through a second cementing stage clamp to perform secondary cementing includes:

[0041] The opening plug of the second cementing stage collar is inserted into the wellhead. The wellhead is pressurized until the opening plug abuts against the opening sleeve of the second cementing stage collar, thus opening the injection hole of the second cementing stage collar. Cement slurry is pumped into the well from the wellhead. Then, the closing plug of the second cementing stage collar is inserted into the wellhead, and displacement fluid is pumped into the well from the wellhead. This causes the closing plug of the second cementing stage collar to push the cement slurry downwards, through the injection hole of the second cementing stage collar, into the second annulus, until the closing plug abuts against the closing sleeve of the second cementing stage collar. Then, the injection hole is closed, so that all the cement slurry enters the second annulus.

[0042] According to another aspect of the present invention, a device for preventing deformation of casing in gypsum-salt rock strata is provided, comprising:

[0043] The first packer is installed on the outside of the casing below the enlarged section of the gypsum-salt rock formation. The first packer separates the first annulus formed by the casing in the first well section below the enlarged section from the enlarged annulus formed on the outside of the casing in the enlarged section. Cement slurry of a corresponding volume is injected into the first annulus for primary cementing.

[0044] The first cementing stage collar is located below the enlarged section and connected to the first packer above the first packer. The first cementing stage collar fills the enlarged annulus with a corresponding volume of equal pressure-bearing medium.

[0045] A second packer, disposed on the outside of the casing above the enlarged section in the gypsum-salt rock formation, separates the equalizing pressure-bearing medium within the enlarged annulus from the second annulus formed outside the casing in the second well section above the enlarged section; and

[0046] The second cementing stage collar, which is located above the enlarged section of the gypsum-salt rock stratum and connected to the second packer above the second packer, injects cement slurry into the second annulus for secondary cementing.

[0047] In one embodiment of the present invention, a first cementing stage collar is connected to a first packer via a first casing stub, and a second cementing stage collar is connected to a second packer via a second casing stub.

[0048] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0049] This invention utilizes an innovative combination of existing market components and materials to achieve, with minimal increase in cost and simple operation, the filling of the enlarged annulus in the uncemented section of the gypsum-salt rock formation with a balanced pressure-bearing medium that provides isolation and corrosion protection, thereby preventing casing deformation and corrosion. Attached Figure Description

[0050] Figure 1 A flowchart of a method for preventing casing deformation in gypsum-salt rock strata provided by an embodiment of the present invention is shown;

[0051] Figure 2 A schematic diagram of a device for preventing casing deformation in gypsum-salt rock strata provided in an embodiment of the present invention is shown;

[0052] Figure 3 It shows the use of Figure 2 A schematic diagram of the device during the first-stage cementing and injection of equalizing pressure-bearing medium into the enlarged annulus.

[0053] Figure 4 Is Figure 3 A schematic diagram of the device during secondary cementing based on the existing device.

[0054] List of reference numerals

[0055] Steps S101, S102, S103, S104, S105, S106, S107, S108, S109; 1001 Drilling Diameter Section; 1002 Enlarged Section of Gypsum-Salt Rock Formation; 1003 Casing; 1004 Wellhead Equipment; 1005 First Packer; 1006 First Cementing Stage Hoop; 1007 Second Packer; 1008 Second Cementing Stage Hoop; 1009 First Well Section; 1010 Second Well Section; 1011 First Annulus; 1012 Second Annulus; 1013 Enlarged Annulus; 1014 First Cementing Top Plug; 10 15 Cement slurry during the first stage cementing process; 1016 Opening plug of the first cementing stage collar; 1017 Opening sleeve of the first cementing stage collar; 1018 Closing sleeve of the first cementing stage collar; 1019 Injection hole of the first cementing stage collar; 1020 Equalizing pressure-bearing medium; 1021 Closing plug of the first cementing stage collar; 1022 Opening sleeve of the second cementing stage collar; 1023 Injection hole of the second cementing stage collar; 1024 Closing sleeve of the second cementing stage collar; 1025 Opening plug of the second cementing stage collar; 1026 Closing plug of the second cementing stage collar; 1027 Cement slurry during the second stage cementing process. Detailed Implementation

[0056] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0057] like Figure 1-4 As shown, the present invention provides a method for preventing casing deformation in gypsum-salt rock strata, comprising:

[0058] Step S101: Complete drilling and enlarge the borehole in the gypsum-salt rock section to obtain the enlarged section 1002 of the gypsum-salt rock section;

[0059] Step S102: Obtain the first well section 1009 below the enlarged section 1002, the second well section 1010 above the enlarged section 1002, the first annulus 1011 formed outside the casing in the first well section 1009, the second annulus 1012 formed outside the casing in the second well section 1010, and the enlarged annulus 1013 formed outside the casing in the enlarged section 1002;

[0060] Step S103: Provide a first cementing stage collar 1006 and a first packer 1005 outside the casing below the enlarged section 1002, and provide a second cementing stage collar 1008 and a second packer 1007 outside the casing above the enlarged section 1002;

[0061] Step S104: Inject cement slurry 1015 of the corresponding space volume into the first annulus 1011 to perform primary cementing;

[0062] Step S105: Separate the cement slurry 1015 in the first annulus 1011 from the enlarged annulus 1013 using the first packer 1005;

[0063] Step S106: Fill the enlarged annulus 1013 with a corresponding volume of equal pressure-bearing medium 1020 through the first cementing stage collar 1006;

[0064] Step S107: Separate the equalizing pressure-bearing medium 1020 in the expanded annulus 1013 from the second annulus 1012 by the second packer 1007;

[0065] Step S108: Inject cement slurry 1027 into the second annulus 1012 through the second cementing stage clamp 1008 to perform secondary cementing; and

[0066] Step S109: Solidify the cement slurry 1015 in the first-stage cementing process and the cement slurry 1027 in the second-stage cementing process.

[0067] In the above method, step S101 includes:

[0068] After the basic wellbore is completed, the diameter of the wellbore in the gypsum-salt layer and the well section above and below it is expanded using a reaming bit. The degree of expansion is determined according to the proportion of gypsum in the gypsum-salt layer.

[0069] In the above method, step S101 specifically involves using a reaming drill bit to expand the diameter of the gypsum-salt layer and the 20m well sections above and below it from 190.5mm to 215.9mm.

[0070] In the above method, in step S103, the first packer 1005 is located 5m below the reaming section, and the second packer 1007 is located 5m above the reaming section.

[0071] In the above method, in step S103, the first cementing stage collar 1006 is connected to the first packer 1005 through the first casing stub, and the second cementing stage collar 1008 is connected to the second packer 1007 through the second casing stub.

[0072] In the above method, the lengths of the first and second sleeve short sections in step S103 are both 1m.

[0073] In the above method, the pressure at which the first packer 1005 opens and closes is less than the sum of the pressure at which the second packer 1007 opens and closes and the pressure of the liquid column between the first packer 1005 and the second packer 1007.

[0074] In the above method, the balanced pressure-bearing medium 1020 is selected based on its resistance to high temperature and high pressure, water resistance, adhesion, rheological properties, performance in balancing pressure loads, and product price.

[0075] In the above method, the equalizing pressure-bearing medium 1020 has long-term stable high-temperature and high-pressure resistance performance under high temperature of 120℃ and high pressure of 35MPa.

[0076] In the above method, the pressure-bearing medium 1020 includes oil-based gel materials.

[0077] In the above method, the pressure-bearing medium 1020 includes soap-based thickened hydrocarbon materials.

[0078] In the above method, the equalizing pressure-bearing medium 1020 is lithium-based grease No. 3.

[0079] In the above method, step S105 includes:

[0080] Displacement fluid is continuously injected from the wellhead into the casing and pressurized to the opening pressure of the first packer 1005 to cause the rubber sleeve of the first packer 1005 to expand. Then the first packer 1005 is closed, thereby keeping the cement slurry 1015 in the first annulus 1011 separated from the enlarged annulus 1013.

[0081] In the above method, step S106 includes:

[0082] The opening plug 1016 of the first cementing stage collar is inserted into the wellhead. The wellhead is pressurized until the opening plug 1016 abuts against the opening sleeve 1017 of the first cementing stage collar, thus opening the injection hole 1019 of the first cementing stage collar. The equalizing pressure-bearing medium 1020 is pumped into the well from the wellhead. Then, the closing plug 1021 of the first cementing stage collar is inserted into the wellhead, and displacement fluid is pumped into the well from the wellhead. This causes the closing plug 1021 of the first cementing stage collar to push the equalizing pressure-bearing medium 1020 downward, through the injection hole 1019 of the first cementing stage collar, into the enlarged annulus 1013, until the closing plug 1021 abuts against the closing sleeve 1018 of the first cementing stage collar, thus closing the injection hole 1019. In this way, all the equalizing pressure-bearing medium 1020 enters the enlarged annulus 1013.

[0083] In the above method, step S107 includes:

[0084] Displacement fluid is continuously injected from the wellhead into the casing and pressurized to the opening pressure of the second packer 1007 to cause the rubber sleeve of the second packer 1007 to expand. Then the second packer 1007 is closed to keep the balanced pressure-bearing medium 1020 in the enlarged annulus 1013 separated from the second annulus 1012.

[0085] In the above method, step S108 includes:

[0086] The opening plug 1025 of the second cementing stage collar is inserted into the wellhead. The wellhead is pressurized until the opening plug abuts against the opening sleeve 1022 of the second cementing stage collar, thereby opening the injection hole 1023 of the second cementing stage collar. Cement slurry 1027 is pumped into the well from the wellhead. Subsequently, the closing plug 1026 of the second cementing stage collar is inserted into the wellhead, and displacement fluid is pumped into the well from the wellhead. This causes the closing plug 1026 of the second cementing stage collar to push the cement slurry 1027 downward, through the injection hole 1023 of the second cementing stage collar, into the second annulus 1012, until the closing plug 1026 abuts against the closing sleeve 1024 of the second cementing stage collar. Then, the injection hole 1023 is closed, so that all the cement slurry 1027 enters the second annulus 1012.

[0087] The above method further includes:

[0088] After the cement slurry 1015 in the first cementing process and the cement slurry 1027 in the second cementing process have solidified, the drilling tool is lowered into the casing to drill out the opening plug 1016 and closing plug 1021 of the first cementing stage collar and the opening plug 1025 and closing plug 1026 of the second cementing stage collar, and the well is then circulated to the bottom of the well.

[0089] like Figure 2-4 As shown, a device for preventing casing deformation in gypsum-salt rock strata is provided, comprising:

[0090] The first packer 1005 is disposed on the outside of the casing below the enlarged section 1002 of the gypsum-salt rock layer. The first packer 1005 separates the first annulus 1011 formed by the casing in the first well section 1009 below the enlarged section 1002 from the enlarged annulus 1013 formed outside the casing in the enlarged section 1002. Cement slurry 1015 of a corresponding volume is injected into the first annulus 1011 for primary cementing.

[0091] The first cementing stage collar 1006 is located below the enlarged section 1002 and connected to the first packer 1005 above it. The first cementing stage collar 1006 fills the enlarged annulus 1013 with a corresponding volume of equal pressure-bearing medium 1020.

[0092] A second packer 1007 is disposed on the outside of the casing above the enlarged section 1002 in the gypsum-salt rock formation. The second packer 1007 separates the equalizing pressure-bearing medium 1020 within the enlarged annulus 1013 from the second annulus 1012 formed outside the casing in the second well section 1010 above the enlarged section 1002.

[0093] The second cementing stage collar 1008 is located above the enlarged section 1002 of the gypsum-salt rock layer and is connected to the second packer 1007 above the second packer 1007. The second cementing stage collar 1008 injects cement slurry 1027 into the second annulus 1012 for secondary cementing.

[0094] In the above-mentioned device, the first cementing stage collar 1006 is connected to the first packer 1005 through the first casing stub, and the second cementing stage collar 1008 is connected to the second packer 1007 through the second casing stub.

[0095] In the above-mentioned device, the length of both the first and second sleeve sections is 1m.

[0096] The technical solutions described in this application will be explained in detail below through specific embodiments.

[0097] This application will be described in terms of the following three aspects:

[0098] 1. Select a pressure-balancing medium 1020 with isolation and corrosion protection functions. The performance requirements of this pressure-balancing medium 1020 need to meet the following aspects:

[0099] A. It has high temperature and high pressure resistance. The gypsum-salt rock formations in my country's oil and gas fields are quite deep, and the formations are usually in the range of temperature 80℃-200℃ and pressure 20-50MPa. In this application example, the medium needs to be stable for a long time under high temperature of 120℃ and high pressure of 35MPa.

[0100] B. It has water-resistant properties and does not mix with water of any mineralization at the temperature of the gypsum-salt rock section.

[0101] C. It has adhesion properties. At the temperature of the gypsum-salt rock section, it has good adhesion to the casing steel and the gypsum-salt rock of the formation, so that the gypsum-salt rock no longer comes into contact with water, and the outer wall of the casing no longer comes into contact with the highly mineralized water dissolved in the gypsum-salt rock.

[0102] D. It has rheological properties and good shear-thinning fluidity under high pressure differential, which facilitates the injection of the medium into the annulus between the casing and the formation through small channels; it has high viscosity under lower pressure differential, which facilitates the complete displacement of the original drilling mud in the annulus between the casing and the formation from bottom to top.

[0103] E. It has the ability to balance pressure load. When the gypsum-salt rock formation experiences local stress changes that generate load, the medium can transmit the pressure to the entire filling space, so that the pressure outside the casing is balanced and no deformation occurs. Therefore, it cannot be solid materials such as cementing.

[0104] F. The price is reasonable and acceptable.

[0105] By screening existing commercially available or commercially available compound materials according to the above six performance requirements, oil-based gel materials were determined to be the applicable type, especially soap-based thickened hydrocarbon materials, which have good applicability and can achieve different levels of performance requirements by adjusting the composition. For the performance requirements of this application example, lithium-based grease No. 3 is preferred. This material has long-term colloidal stability under conditions of temperature ≤180℃ and pressure ≤130MPa. Its water resistance, adhesion, and rheological properties all meet the requirements, and it can achieve the purpose of balancing pressure load to prevent sleeve deformation and isolation and corrosion protection.

[0106] 2. Design a device capable of filling the annulus cavity with the aforementioned medium.

[0107] A device assembly can be designed to fill the annulus 1013 of the expanded hole uncemented section in the gypsum-salt rock formation with a balanced pressure-bearing medium 1020 that has an isolation and anti-corrosion function. All the devices mentioned are commercially available standard components that can be used by technicians in the industry.

[0108] The device formed by the combination of components and its functions are as follows:

[0109] like Figure 2-4 As shown, the device includes:

[0110] The first packer 1005 is located on the outside of the casing at a position 5m below the enlarged section 1002 of the gypsum-salt rock layer. The first packer 1005 separates the first annulus 1011 formed by the casing in the first well section 1009 below the enlarged section 1002 from the enlarged annulus 1013 formed outside the casing in the enlarged section 1002. Cement slurry 1015 of a corresponding volume is injected into the first annulus 1011 for primary cementing.

[0111] The first cementing stage collar 1006 is located below the enlarged section 1002 and above the first packer 1005, and is connected to the first packer 1005 via a 1m casing short section. The first cementing stage collar 1006 fills the enlarged annulus 1013 with a corresponding volume of equal pressure-bearing medium 1020.

[0112] The second packer 1007 is disposed on the outside of the casing 5m above the enlarged section 1002 in the gypsum-salt rock stratum. The second packer 1007 separates the equalizing pressure-bearing medium 1020 within the enlarged annulus 1013 from the second annulus 1012 formed outside the casing in the second well section 1010 above the enlarged section 1002.

[0113] The second cementing stage collar 1008 is located above the enlarged section 1002 of the gypsum-salt rock layer and is connected to the second packer 1007 above the second packer 1007 via a 1m casing short section. The second cementing stage collar 1008 injects cement slurry 1027 into the second annulus 1012 for secondary cementing.

[0114] 3. The steps for completing the medium filling of the enlarged annulus are as follows:

[0115] for Figure 2 The drilling section 1001 and wellhead device 1004 shown constitute the basic drilling framework. After the basic wellbore is completed, the wellbore diameter of the gypsum-salt layer and the well section above and below it of 20m is expanded to 215.9mm using a reaming bit to obtain the reaming section 1002 of the gypsum-salt rock layer.

[0116] like Figure 2 As shown, after drilling and enlarging the gypsum-salt rock formation, a casing string assembly equipped with the aforementioned device that can fill the selected medium into the enlarged annulus is run in to obtain the first well section 1009 below the enlarged section 1002, the second well section 1010 above the enlarged section 1002, the first annulus 1011 formed outside the casing in the first well section 1009, the second annulus 1012 formed outside the casing in the second well section 1010, and the enlarged annulus 1013 formed outside the casing in the enlarged section 1002. Cement slurry 1015 of the corresponding space volume is injected into the first annulus 1011 for primary cementing.

[0117] like Figure 3 As shown, a primary cementing plug 1014 is installed at the bottom of the casing 1003. Without primary cementing and waiting for the cement to set, displacement fluid is continuously injected into the casing from the wellhead. The pressure is increased to the opening pressure of the first packer 1005, causing the rubber sleeve of the first packer 1005 to expand. Then, the first packer 1005 is closed, thereby maintaining the separation between the cement slurry 1015 in the first annulus 1011 and the enlarged annulus 1013. The opening plug 1016 of the first cementing stage collar is then inserted into the wellhead. The wellhead is pressurized until the opening plug 1016 abuts against the opening sleeve 1017 of the first cementing stage collar, opening the injection hole 1019 of the first cementing stage collar. The designed amount of balanced pressure-bearing medium 1020 (in this embodiment, lithium-based grease No. 3) with isolation and anti-corrosion function is pumped into the well. Then, the closing plug 1021 of the first cementing stage collar is inserted into the wellhead. Subsequently, displacement fluid is pumped into the wellhead to replace the closing plug 1021 of the first cementing stage collar and push the balanced pressure-bearing medium 1020 downward. It enters the enlarged annulus 1013 through the injection hole 1019 of the first cementing stage collar until the closing plug 1021 presses against the closing sleeve 1018 of the first cementing stage collar and closes the injection hole 1019. In this way, all the balanced pressure-bearing medium 1020 enters the enlarged annulus 1013.

[0118] like Figure 4As shown, displacement fluid is continuously injected into the casing from the wellhead, pressurizing it to the opening pressure of the second packer 1007, causing the rubber sleeve of the second packer 1007 to expand and close the second packer 1007. This maintains the separation of the balanced pressure-bearing medium 1020 in the enlarged annulus 1013 from the second annulus 1012. Thus, the balanced pressure-bearing medium 1020 in the enlarged annulus of the casing and the gypsum-salt rock formation is separated from the liquid in the upper second annulus 1012 and the lower first annulus 1011. The opening plug 1025 of the second cementing stage collar is then inserted into the wellhead, and the wellhead is pressurized until the opening plug 1025 abuts against the opening sleeve 102 of the second cementing stage collar. 2. Open the injection hole 1023 of the second cementing stage collar, pump the designed amount of cementing slurry 1027 for this section into the well from the wellhead, then put the closing plug 1026 of the second cementing stage collar into the wellhead, and pump the displacement fluid into the well from the wellhead. The displacement fluid replaces the closing plug 1026 of the second cementing stage collar and pushes the cementing slurry 1027 downward. It enters the second annulus 1012 through the injection hole 1023 of the second cementing stage collar until the closing plug 1026 pushes against the closing sleeve 1024 of the second cementing stage collar. Then the injection hole 1023 is closed, so that all the designed amount of cementing slurry 1027 for this section enters the second annulus 1012.

[0119] After the cement slurry 1015 in the first annulus 1011 and the cement slurry 1027 in the second annulus 1012 solidify, drill string is lowered into the casing to remove the opening plug 1016 and closing plug 1021 of the first cementing stage collar and the opening plug 1025 and closing plug 1026 of the second cementing stage collar, and the well is circulated to the bottom of the well.

[0120] In summary, this invention, through innovative combination and application of existing market components and materials, achieves the purpose of filling the annulus of the enlarged hole in the uncemented section of the gypsum-salt rock formation with a balanced pressure-bearing medium that provides isolation and corrosion protection, thereby preventing casing deformation and corrosion, with only a slight increase in cost and simple and easy operation.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for preventing casing deformation in gypsum-salt rock strata, characterized in that, include: Complete drilling and enlarge the borehole in the gypsum-salt rock section to obtain the enlarged section of the gypsum-salt rock section; Obtain the first well section below the enlarged section, the second well section above the enlarged section, the first annulus formed outside the casing in the first well section, the second annulus formed outside the casing in the second well section, and the enlarged annulus formed outside the casing in the enlarged section; A first cementing stage collar and a first packer outside the casing are provided below the enlarged section, and a second cementing stage collar and a second packer outside the casing are provided above the enlarged section; Cement slurry of a corresponding volume is injected into the first annulus for primary cementing. The cement slurry in the first annulus is separated from the enlarged annulus by the first packer; The first cementing stage collar fills the enlarged annulus with a corresponding volume of balanced pressure-bearing medium that has an isolating and anti-corrosion function, so that the gypsum-salt rock no longer comes into contact with water and continues to undergo dissolution and hydration reactions, thereby achieving the purpose of preventing casing deformation and corrosion. The balanced pressure-bearing medium has water resistance properties that are not miscible with water of any mineralization at the formation temperature of the gypsum-salt rock section, adhesion properties that adhere to the casing steel and the formation gypsum-salt rock at the formation temperature of the gypsum-salt rock section, and rheological properties. The balanced pressure-bearing medium includes oil-based gel materials. The second packer separates the balanced pressure-bearing medium in the enlarged annulus from the second annulus. Secondary cementing is performed by injecting cement slurry into the second annulus through the second cementing stage clamp; as well as The cement slurry used in the primary cementing and secondary cementing processes is solidified.

2. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The first packer is located 5 m below the enlarged section, and the second packer is located 5 m above the enlarged section.

3. The method for preventing casing deformation in gypsum-salt rock strata according to claim 2, characterized in that, The first cementing stage collar is connected to the first packer via a first casing stub, and the second cementing stage collar is connected to the second packer via a second casing stub.

4. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The pressure at which the first packer opens and closes is less than the sum of the pressure at which the second packer opens and closes and the pressure of the liquid column between the first packer and the second packer.

5. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The balanced pressure-bearing medium is selected based on its resistance to high temperature and high pressure, water resistance, adhesion, rheological properties, performance in balancing pressure loads, and product price.

6. The method for preventing casing deformation in gypsum-salt rock strata according to claim 5, characterized in that, The pressure-bearing medium includes soap-based thickened hydrocarbon materials.

7. The method for preventing casing deformation in gypsum-salt rock strata according to claim 5, characterized in that, The pressure-bearing medium is lithium-based grease No.

3.

8. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The step of separating the cement slurry in the first annulus from the enlarged annulus using the first packer includes: Displacement fluid is continuously injected into the casing from the wellhead and pressurized to the opening pressure of the first packer to cause the first packer sleeve to expand. Then the first packer is closed, thereby keeping the cement slurry in the first annulus separated from the enlarged annulus.

9. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The step of filling the enlarged annulus with a corresponding volume of equalizing pressure-bearing medium through the first cementing stage collar includes: The opening plug of the first cementing stage collar is inserted into the wellhead. The wellhead is pressurized until the opening plug abuts against the opening sleeve of the first cementing stage collar, thus opening the injection hole of the first cementing stage collar. The equalizing pressure-bearing medium is pumped into the well from the wellhead. Then, the closing plug of the first cementing stage collar is inserted into the wellhead, and displacement fluid is pumped into the well from the wellhead. This causes the closing plug of the first cementing stage collar to push the equalizing pressure-bearing medium downwards, entering the enlarged annulus through the injection hole of the first cementing stage collar, until the closing plug abuts against the closing sleeve of the first cementing stage collar, thus closing the injection hole. In this way, all the equalizing pressure-bearing medium enters the enlarged annulus.

10. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The step of separating the equalizing pressure-bearing medium in the expanded annulus from the second annulus using the second packer includes: Displacement fluid is continuously injected from the wellhead into the casing, pressurizing it to the opening pressure of the second packer to cause the second packer sleeve to expand. Then the second packer is closed to maintain the balanced pressure-bearing medium in the enlarged annulus and separate it from the second annulus.

11. The method for preventing casing deformation in gypsum-salt rock strata according to claim 1, characterized in that, The steps of injecting cement slurry into the second annulus through the second cementing stage clamp to perform secondary cementing include: The opening plug of the second cementing stage collar is inserted into the wellhead. The wellhead is pressurized until the opening plug abuts against the opening sleeve of the second cementing stage collar, thus opening the injection hole of the second cementing stage collar. Cement slurry is pumped into the well from the wellhead. Then, the closing plug of the second cementing stage collar is inserted into the wellhead, and displacement fluid is pumped into the well from the wellhead. This causes the closing plug of the second cementing stage collar to push the cement slurry downwards, through the injection hole of the second cementing stage collar, into the second annulus, until the closing plug abuts against the closing sleeve of the second cementing stage collar. Then, the injection hole is closed, so that all the cement slurry enters the second annulus.

12. A device for preventing deformation of casing in gypsum-salt rock strata, characterized in that, include: The first packer is located on the outside of the casing below the enlarged section of the gypsum-salt rock formation. The first packer separates the first annulus formed by the casing in the first well section below the enlarged section from the enlarged annulus formed on the outside of the casing in the enlarged section. Cement slurry of a corresponding volume is injected into the first annulus for primary cementing. The first cementing stage collar is located below the enlarged section and connected to the first packer above it. The first cementing stage collar fills the enlarged annulus with a corresponding volume of a balanced pressure-bearing medium with isolation and anti-corrosion function, so that the gypsum-salt rock no longer comes into contact with water and continues to undergo dissolution and hydration reactions, thereby preventing casing deformation and corrosion. The balanced pressure-bearing medium has water resistance properties that are not miscible with water of any mineralization at the formation temperature of the gypsum-salt rock section, adhesion properties that adhere to the casing steel and the formation gypsum-salt rock at the formation temperature of the gypsum-salt rock section, and rheological properties. The balanced pressure-bearing medium includes oil-based gel materials. The second packer is disposed on the outside of the casing above the enlarged section of the gypsum-salt rock formation. The second packer separates the equalizing pressure-bearing medium in the enlarged annulus from the second annulus formed outside the casing in the second well section above the enlarged section. as well as The second cementing stage collar, the second packer is positioned above the enlarged section of the gypsum-salt rock layer and connected to the second packer above the second packer, the second cementing stage collar injects cement slurry into the second annulus for secondary cementing.

13. The device for preventing casing deformation in gypsum-salt rock strata according to claim 12, characterized in that, The first cementing stage collar is connected to the first packer via a first casing stub, and the second cementing stage collar is connected to the second packer via a second casing stub.

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