Variable-density foam cement slurry well cementation method and well completion structure

Abstract

The invention provides a variable-density foam cement slurry well cementation method and a well completion structure, and belongs to the technical field of oil exploration. The well completion structure comprises an oil and gas well borehole and a casing pipe, an annulus is formed between the oil and gas well borehole and the casing pipe, and a cement sheath and a foam cement sheath are arranged on the horizontal section of the annulus at intervals in the well depth direction. By reducing the elastic modulus and the strength of the cement sheath between the casing and the stratum, when shear sliding displacement occurs on the stratum fracture surface, the low elastic modulus and the low strength of the foam cement sheath form a buffering effect between the stratum and the casing, so that the load acting on the casing is reduced, and the deformation of the casing is prevented or reduced; the section losing and well abandoning risks caused by casing deformation are reduced, and the oil and gas exploitation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum exploration, and in particular relates to a variable-density foam cement slurry cementing method and a well completion structure. Background Art

[0002] The problem of casing deformation in oil and gas well fracturing is a global problem that needs to be solved urgently. In the shale gas blocks of Weiyuan and Changning in the Sichuan Basin, the number of wells with casing deformation even exceeds 50%. Casing deformation causes a reduction in the number of fracturing stages, and the production and recovery rate of oil and gas single wells are seriously reduced.

[0003] The current research results on the deformation of fracturing casing show that the main reason for casing deformation is that the fracturing fluid activates the formation to produce formation slippage and shears the oil and gas well casing, resulting in shear deformation of the casing. In the early stage, many methods for preventing the deformation of oil and gas well casing have been proposed, such as: (1) Reducing the fracturing pump pressure can reduce fracture activation and slippage, but the reduction in pump pressure affects the fracturing effect; (2) Shielding temporary gambling technology is used to prevent fracturing fluid from entering natural fractures and prevent fracture activation and slippage. The field application effect of this method is not obvious, and the fractures still have large slippage; (3) Reducing the elastic modulus of the outer material of the casing and using the method of wrapping the outer casing with rubber to reduce the shear load of the casing, the effect is not obvious; (4) By reducing the elastic modulus of the cement ring and using the floating bead cement slurry system, the casing deformation is alleviated to a certain extent, but the effect is not obvious; (5) By increasing the strength of the casing steel, increasing the casing wall thickness, reducing the inner diameter of the casing, etc., the casing's anti-extrusion and shear strength are increased. The problem of casing deformation in oil and gas wells has not been solved, and the problem of casing deformation caused by oil and gas well fracturing still exists in large quantities.

[0004] Low-density foam cement slurry has the characteristics of low elastic modulus and low strength, but its sealing ability to the annulus is limited under the action of fracturing load. Conventional cement slurry has a large elastic modulus and high strength, and has good sealing ability in the annulus.

[0005] Therefore, it is urgent to find a cementing method and a completion structure to solve the problem of deformation of the fracturing casing of oil and gas wells. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned problems existing in the prior art, and to provide a variable density foam cement slurry cementing method and a completion structure, which solves the problem of deformation of the existing oil and gas well fracturing casing.

[0007] The present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention provides a variable density foam cement slurry completion structure, including an oil and gas wellbore and a casing, an annulus is formed between the oil and gas wellbore and the casing, and a cement ring and a foam cement ring are arranged at intervals in the horizontal section of the annulus along the well depth direction.

[0009] A further improvement of the present invention is:

[0010] The cement sheath is formed by injecting cement slurry into the annulus between the wellbore and the casing of an oil and gas well; and / or,

[0011] The cement sheath is located between the two fracturing stages.

[0012] A further improvement of the present invention is:

[0013] The foam cement sheath is located at the position of the fracturing section, and the length of the foam cement sheath is the same as or close to the length of the fracturing section.

[0014] A further improvement of the present invention is:

[0015] The foam cement annulus is formed by injecting foam cement slurry into the annulus between the wellbore and the casing of an oil and gas well; and / or,

[0016] Foam cement slurry is based on cement slurry and is formed by adding foaming agent, foam stabilizer and nitrogen to the cement slurry.

[0017] A further improvement of the present invention is:

[0018] The contents of the components in the foam cement slurry are: 100 parts by weight of cement slurry, 6-12 parts by weight of foaming agent, 3-6 parts by weight of foam stabilizer, and the volume ratio of cement slurry to nitrogen is 1:30-80.

[0019] A further improvement of the present invention is:

[0020] The foaming agent is a protein foaming agent or a compound of a protein foaming agent and an ionic surfactant; preferably, the ionic surfactant is selected from one or more of sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine and sodium α-olefin sulfonate.

[0021] A further improvement of the present invention is:

[0022] The foam stabilizer is selected from one or more of carboxymethyl cellulose, polyanionic cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose and hydroxyethyl methyl cellulose.

[0023] A further improvement of the present invention is:

[0024] The density of foam cement slurry is 0.3-1.2g / cm lower than that of cement slurry base slurry. 3 .

[0025] A further improvement of the present invention is:

[0026] The strength of foam cement slurry is 5~15MPa.

[0027] A second aspect of the present invention provides a variable density foam cement slurry cementing method, comprising the following steps:

[0028] The first step is to design the location and amount of the foam cement slurry according to the location and length of the fracturing section, wherein the foam cement slurry is located in the fracturing section and the conventional cement slurry is located between the two fracturing sections;

[0029] Step 2: After the wellbore and ground preparation work is completed, cementing construction begins. First, the designed amount of spacer fluid is injected, and then the designed amount of conventional cement slurry and foam cement slurry are injected at intervals along the well depth direction in the horizontal section of the annulus formed between the wellbore and the casing;

[0030] Step 3: After the cement slurry injection is completed, the slurry replacement operation is carried out;

[0031] The fourth step is to shut down the well or open the well to wait for solidification after the slurry replacement is completed. After the solidification is completed, subsequent well operations are carried out and the fracturing section is located in the foam cement slurry section.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The deformation of the casing of oil and gas well fracturing is mainly caused by the shear deformation of the casing caused by the formation sliding caused by fracturing. It is the main method to solve the deformation of the casing of oil and gas well fracturing when reducing the formation sliding displacement and the casing load and deformation. The present invention reduces the elastic modulus and strength of the cement ring between the casing and the formation. When shear sliding displacement occurs on the formation fracture surface, the low elastic modulus and low strength of the foam cement stone form a buffering effect between the formation and the casing, reducing the load on the casing, preventing or reducing the deformation of the casing, reducing the risk of losing sections and abandoning wells caused by casing deformation, and improving the efficiency of oil and gas production.

[0034] (2) The cementing method provided by the present invention uses cement rings in the non-fracturing section to seal the wellbore, without the need to attach any device to the casing, and does not produce additional impact and risk on the safe lowering of the casing and subsequent construction. The foam cement slurry in the well can be distributed according to the designed intervals, and the density of the foam cement slurry and the length in the well can be adjusted. The operation is simple, and the cementing method is feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention provides a schematic diagram of a variable density foam cement slurry completion structure.

[0036] In the figure, 1. casing, 2. cement ring, 3. foam cement ring. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0038] In order to effectively solve the problem of casing deformation during the fracturing process of oil and gas wells, the present invention combines the characteristics of low elastic modulus and low compressive strength of foam cement stone. When the formation shear sliding load caused by fracturing acts on the casing-cement ring system, the foam cement stone strength can be destroyed, forming a buffer zone between the formation rock and the casing to reduce the shear deformation of the casing. At the same time, due to the low strength of foam cement stone, the fracturing fluid is easy to cause cement ring damage, causing the fracturing fluid to flow in the wellbore annulus. The foam cement in the production layer section still needs to have a certain sealing ability. Therefore, it is considered to use a segmented variable density foam cement slurry system in the fracturing section, which not only ensures the wellbore annulus sealing ability, but also prevents the problem of deformation of the oil and gas well fracturing casing.

[0039] [Example 1]

[0040] like Figure 1 As shown, the present invention provides a variable density foam cement slurry completion structure, including an oil and gas wellbore and a casing 1, an annulus is formed between the oil and gas wellbore and the casing 1, and a horizontal section of the annulus is provided with conventional cement slurry and foam cement slurry at intervals along the well depth direction to form a cement ring 2 and a foam cement ring 3, and the foam cement ring 3 is located at the position of the fracturing section.

[0041] The deformation of the fracturing casing of an oil and gas well is mainly due to the sliding displacement caused by the cracks in the formation activated by fracturing. The present invention forms a cement ring 2 and a foam cement ring 3 in the horizontal section of the annulus between the wellbore and the casing of the oil and gas well, and the foam cement ring 3 is located in the fracturing section. When the formation undergoes shear sliding displacement along the cracks, the foam cement ring 3 is squeezed and crushed, forming a buffer zone between the formation rock and the casing 2, reducing the shear load acting on the casing 1, and achieving the purpose of preventing the casing from deformation.

[0042] The casing 1 is a metal casing used in oil and gas wells. The parameters of the metal casing, such as the steel grade, wall thickness, and strength, are consistent with those of currently used casings and will not be described in detail here.

[0043] [Example 2]

[0044] The cement ring 2 is formed by injecting cement slurry into the annulus between the wellbore and the casing 1 of the oil and gas well. The cement slurry is various cement slurry systems commonly used for cementing, and can be low-density cement slurry, conventional density cement slurry and high-density cement slurry.

[0045] In the present invention, cement ring 2 and foam cement ring 3 are arranged at intervals in the horizontal section of the annulus, wherein the cement ring 2 is used to seal the annulus to prevent the fluid in the formation from flowing in the annulus, and is located between two fracturing sections. Preferably, the length of each cement ring 2 in the horizontal section of the annulus is 10-30 meters.

[0046] [Example 3]

[0047] Each section of the foam cement annulus 3 in the annulus between the wellbore and the casing 1 of the oil and gas well is located at the position of the fracturing section, and the length of the foam cement annulus 3 is the same as or close to the length of the fracturing section.

[0048] The fracturing stage will perform perforation and fracturing operations, which will cause the foam cement ring to be damaged and lose its sealing ability. The role of the foam cement ring 3 in the annulus is mainly to play a buffering role, reduce the casing load caused by formation sliding to prevent casing deformation. The sealing ability of the foam cement ring is poor, and the conventional cement ring is used to seal the annulus. Therefore, the foam cement ring is used in the fracturing stage and the conventional cement ring is used in the non-fracturing stage. Even if the foam cement ring is damaged during the perforation and fracturing process, the conventional cement ring used in the non-fracturing stage will also ensure the sealing ability of the entire annulus.

[0049] The foam cement annulus 3 is formed by injecting foam cement slurry into the annulus between the wellbore and the casing of the oil and gas well. The foam cement slurry is formed by adding a foaming agent, a foam stabilizer and nitrogen to the cement slurry with cement slurry as the base slurry.

[0050] The contents of the components in the foam cement slurry are: 100 parts by weight of cement slurry, 6-12 parts by weight of foaming agent, 3-6 parts by weight of foam stabilizer, and the volume ratio of cement slurry to nitrogen is 1:30-80.

[0051] The foaming agent is a protein foaming agent or a compound of a protein foaming agent and an ionic surfactant; preferably, the ionic surfactant is selected from one or more of sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine and sodium α-olefin sulfonate;

[0052] And / or, the foam stabilizer is selected from one or more of carboxymethyl cellulose, polyanionic cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose and hydroxyethyl methyl cellulose.

[0053] The density of the foam cement slurry is reasonably designed based on the requirements for the strength of cement stone formed by conventional density cement slurry and the strength of the foam cement ring to prevent casing deformation. The lower the density of the foam cement slurry is than that of the conventional density cement slurry, the lower the strength of the foam cement slurry is, and the more beneficial it is to prevent casing deformation. In the present invention, the preferred density of the foam cement slurry is 0.3-1.2 g / cm lower than the density of the cement slurry base slurry. 3 ;The strength of foam cement slurry is 5~15MPa.

[0054] [Example 4]

[0055] The present invention also provides a variable density foam cement slurry cementing method, which specifically comprises the following steps:

[0056] Step 1: Design the cementing slurry column structure, the location of the foamed cement slurry and conventional cement slurry in the well, and the density of the foamed cement slurry;

[0057] The positions of the foam cement slurry and the conventional cement slurry are designed according to the position of the fracturing section in the fracturing design, wherein the foam cement slurry is located in the fracturing section and the conventional cement slurry is located in the non-fracturing section;

[0058] The location design of foam cement slurry and conventional cement slurry in the well is designed according to the length of the fracturing section. The foam cement slurry is injected into the fracturing section, and the conventional cement slurry is injected into the remaining sections.

[0059] The density of the foam cement slurry is reasonably designed based on the requirements for the strength of cement stone formed by conventional density cement slurry and the strength of the foam cement ring to prevent casing deformation. The lower the density of the foam cement slurry is than that of the conventional density cement slurry, the lower the strength of the foam cement slurry is, and the more beneficial it is to prevent casing deformation. In the present invention, the preferred density of the foam cement slurry is 0.3-1.2 g / cm lower than the density of the cement slurry base slurry. 3 ;The strength of foam cement slurry is 5~15MPa;

[0060] Step 2: After the wellbore and ground preparation work is completed, cementing construction begins. First, inject the designed amount of spacer fluid, and then inject the designed amount of conventional cement slurry and foam cement slurry at intervals;

[0061] Among them, the foam cement slurry is formed by injecting a foaming agent, a foam stabilizer and nitrogen into a conventional cement slurry in a foam cement slurry generating device; the injection and stop of the foaming agent, the foam stabilizer and the nitrogen are controlled according to the designed interval foam cement slurry amount to ensure that the length and position of the segmented foam cement slurry in the horizontal section after the cementing construction is completed meet the design requirements;

[0062] The foam cement slurry generating device is a prior art device and will not be described in detail here;

[0063] The spacer fluid is a type of spacer fluid used according to the needs of oil and gas well cementing, which plays an isolating role between the drilling fluid and the cement slurry;

[0064] Step 3: After the cement slurry injection is completed, the slurry replacement operation is carried out;

[0065] The fourth step is to shut down the well or open the well to wait for solidification after the slurry replacement is completed. After the solidification is completed, subsequent well operations are carried out and the fracturing section is located in the foam cement slurry section.

[0066] The deformation of the fracturing casing of oil and gas wells is mainly caused by the shear deformation of the casing caused by the sliding of the formation caused by fracturing. It is the main method to solve the deformation of the fracturing casing of oil and gas wells when reducing the sliding displacement of the formation and the load and deformation of the casing. The present invention reduces the elastic modulus and strength of the cement ring between the casing and the formation. When shear sliding displacement occurs on the fracture surface of the formation, the low elastic modulus and low strength of the foam cement stone form a buffering effect between the formation and the casing, reducing the load on the casing, preventing or reducing the deformation of the casing, reducing the risk of losing sections and abandoning wells caused by casing deformation, and improving the efficiency of oil and gas production.

[0067] The present invention provides a cementing method that uses a cement ring in a non-fracturing section to seal the wellbore without adding any device to the casing, and does not produce additional impact and risk on the safe lowering of the casing and subsequent construction. The foam cement slurry in the well can be distributed according to the designed interval, and the density of the foam cement slurry and the length in the well can be adjusted. The operation is simple, and the cementing method is feasible.

[0068] The cementing method and technical effects of the present invention are further explained below through a specific embodiment.

[0069] [Example 5]

[0070] Well Y1 is a shale gas horizontal well located in southwest China. The shale gas block where the well is located has serious casing deformation problems. The well was completed at a depth of 5899.00m and the drilling fluid density was 1.50g / cm 3 , the vertical section is 0.00~2700.00m, the deflection section is 2700.00~4500.00m, the horizontal section is 4500.00~5899.00m, the well depth of target point A is 4500.00m, the well depth of target point B is 5860.00m, and 34 fracturing sections are designed in the horizontal section, which poses the risk of fracturing casing deformation. It is planned to adopt a variable density foam cement slurry cementing method to prevent fracturing casing deformation, to achieve effective sealing of the well and prevent casing deformation. The specific implementation process is as follows:

[0071] (1) The 4500-5860 m section of this well is the reservoir transformation section. In the fracturing design of this well, a total of 34 fracturing sections are designed. The distance between each fracturing section is 15 m, and each fracturing section is 25 m long. The bottom depth of the first fracturing section is 5860 m, the bottom depth of the second fracturing section is 5820 m, and so on. The bottom depth of each fracturing section is 40 m shallower than the bottom depth of the previous fracturing section, and the length of the fracturing section is 25 m.

[0072] (2) In the production layer cementing design, the isolation fluid used is the oil-washing isolation fluid specially used for shale gas well oil-based mud, with a total of 32m 3 The cement slurry is divided into lead slurry, tail slurry and foam cement slurry; the density of the lead slurry is 1.50g / cm 3 The floating beads low-density cement slurry system is used to seal the vertical section, totaling 60m3 ; Tail slurry density is 1.88g / cm 3 The elastic and tough cement slurry system seals the deflection section, and the tail slurry of the deflection section is 41m in total. 3 ; Foam cement slurry and tailing slurry are distributed in the horizontal section at intervals. According to the fracturing design and the wellbore annulus volume, the conventional cement slurry volume in each horizontal section is 0.34m 3 The amount of foam cement slurry in each section is 0.57m 3 , density of foam cement slurry 1.30g / cm 3 ;

[0073] (3) After the casing is lowered into the well and the drilling fluid circulation is normal and the cementing operation is satisfied, cementing operation begins;

[0074] (4) First, inject wash oil to flush the isolation liquid for 32m 3 ;

[0075] (5) Then the injection density is 1.50g / cm 3 of low-density cement slurry with floating beads, totaling 60m 3 ;

[0076] (6) Then the injection density is 1.88g / cm 3 The elastic and tough cement slurry is used to seal the inclined section, a total of 41m 3 ;

[0077] (7) When the 41m of the sealing and deflecting section 3 After the grouting is completed, the density of the injection is 1.88g / cm 3 The elastic and tough cement slurry is prepared by injecting a foaming agent, a foam stabilizer and nitrogen into the elastic and tough cement slurry flowing through the foam cement slurry generating device to form an interval of foam cement slurry. The specific injection method is as follows:

[0078] ① The volume of the elastic cement slurry between the two sections of foam cement slurry is 0.34m 3 ;

[0079] ②Each section of foam cement slurry base (density 1.88g / cm 3 The volume of the elastic and tough cement paste is 0.57m 3 ;

[0080] ③The density of foam cement slurry is 1.30g / cm 3 , the amount of nitrogen injected is controlled according to the density requirement;

[0081] (8) After the cement slurry injection is completed, the rubber plug is released from the wellhead and 61m of displacement fluid is injected. 3 After the collision pressure;

[0082] (9) After the annulus is pressurized to 15 MPa, the well is shut down and solidified;

[0083] (10) Cementing construction is completed;

[0084] (11) After the setting period is over, the position and length of the foam cement slurry and conventional density cement slurry in the horizontal section of the well are tested, and perforation and fracturing are performed in the foam cement slurry section;

[0085] (12) The fracturing operations of 34 fracturing stages were completed in sequence. The construction was normal without any casing deformation such as bridge plug blockage. The foam cementing was successfully used to solve the problem of casing deformation in oil and gas well fracturing.

[0086] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0087] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0088] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A variable density foam cement slurry completion structure, characterized in that: The invention comprises an oil and gas well bore and a casing, an annulus is formed between the oil and gas well bore and the casing, and a cement ring and a foam cement ring are arranged at intervals in the horizontal section of the annulus along the well depth direction.

2. The variable density foam cement slurry completion structure according to claim 1, characterized in that: The cement annulus is formed by injecting cement slurry into the annulus between the wellbore and the casing of the oil and gas well; and / or, The cement sheath is located between the two fracturing stages.

3. The variable density foam cement slurry completion structure according to claim 2, characterized in that: The foam cement ring is located at the position of the fracturing section, and the length of the foam cement ring is the same as or close to the length of the fracturing section.

4. The variable density foam cement slurry completion structure according to claim 3, characterized in that: The foam cement annulus is formed by injecting foam cement slurry into the annulus between the wellbore and the casing of the oil and gas well; and / or, The foam cement slurry is formed by taking cement slurry as base slurry and adding a foaming agent, a foam stabilizer and nitrogen into the cement slurry.

5. The variable density foam cement slurry completion structure according to claim 4, characterized in that: The contents of the components in the foam cement slurry are: 100 parts by weight of cement slurry, 6-12 parts by weight of foaming agent, 3-6 parts by weight of foam stabilizer, and the volume ratio of cement slurry to nitrogen is 1:30-80.

6. The variable density foam cement slurry completion structure according to claim 3 or 4, characterized in that: The foaming agent is a protein foaming agent or a compound of a protein foaming agent and an ionic surfactant; preferably, the ionic surfactant is selected from one or more of sodium fatty alcohol polyoxyethylene ether sulfate, cocamidopropyl betaine and sodium α-olefin sulfonate.

7. The variable density foam cement slurry completion structure according to claim 3 or 4, characterized in that: The foam stabilizer is selected from one or more of carboxymethyl cellulose, polyanionic cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose and hydroxyethyl methyl cellulose.

8. The variable density foam cement slurry completion structure according to claim 4, characterized in that: The density of the foam cement slurry is 0.3-1.2 g / cm lower than that of the cement slurry base slurry. 3 .

9. The variable density foam cement slurry completion structure according to claim 4, characterized in that: The strength of the foam cement slurry is 5 to 15 MPa.

10. A variable density foam cement slurry cementing method, characterized in that: The following steps are involved: The first step is to design the location and amount of the foam cement slurry according to the location and length of the fracturing section, wherein the foam cement slurry is located in the fracturing section and the conventional cement slurry is located between the two fracturing sections; Step 2: After the wellbore and ground preparation work is completed, cementing construction begins. First, the designed amount of spacer fluid is injected, and then the designed amount of conventional cement slurry and foam cement slurry are injected at intervals along the well depth direction in the horizontal section of the annulus formed between the wellbore and the casing; Step 3: After the cement slurry injection is completed, the slurry replacement operation is carried out; The fourth step is to shut down the well or open the well to wait for solidification after the slurry replacement is completed. After the solidification is completed, subsequent well operations are carried out and the fracturing section is located in the foam cement slurry section.

Images