Fluid loss reducer for drilling fluid, preparation method therefor and use thereof

Abstract

The present invention relates to a fluid loss reducer for a drilling fluid, a preparation method therefor, and a use thereof. The fluid loss reducer comprises a structural unit A, a structural unit B, a structural unit C, and a structural unit D. The fluid loss reducer for a drilling fluid provided by the present invention serves as a fluid loss reducer for a multivalent cation-resistant drilling fluid, exhibits good coalescence stability, and is capable of resisting contamination by various cations such as Ca2+, Mg2+, Al3+ within a certain concentration range, while maintaining the fluid loss control and rheological properties of a water-based drilling fluid system.

Description

Drilling fluid filtration reducers, their preparation methods and applications

[0001] Cross-references to related applications

[0002] This application claims the benefit of Chinese Patent Application No. 202411011564.5, filed on July 26, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to drilling fluid filtration reducers, their preparation methods, and applications. Background Technology

[0004] In recent years, drilling has frequently encountered salt layers, salt-gypsum layers, and highly saline formation water in different blocks. In some blocks, long-term development has resulted in densely packed injection wells and formation pressure disturbances caused by prolonged water injection and acid fracturing. During drilling, the drilling fluid system is easily contaminated by formation fluids mixed with different types of working fluids, leading to performance degradation or even unusability. Furthermore, the inability to accurately determine the type and thickness of salt layers, the location and distribution of formation fluids, and their ionic composition during drilling operations further complicates the problem of drilling fluid contamination. The intrusion of cations, especially high-valence cations, severely affects drilling fluid performance. High-valence cations such as Ca... 2+ Mg 2+ Al 3+ It will displace the Na adsorbed on the surface of bentonite + This leads to a decrease in zeta potential, a thinner hydration film, and reduced repulsion between bentonite particles, resulting in flocculation and coarsening, which easily forms a thick and loose mud cake, causing complex downhole accidents such as differential pressure stuck pipe. When drilling with high-density drilling fluid systems, the invasion of cations is even more severe, leading to a dramatic increase in drilling fluid filtration loss and a high risk of serious downhole accidents such as wellbore collapse. This necessitates the use of filtration control agents that can resist the invasion of multiple cations. Currently, there are many types of filtration control agents used in oilfields, and the performance of each type varies.

[0005] Modified starch-based filtration loss reducers have strong resistance to salt and calcium, but poor temperature resistance, and are essentially ineffective at 120℃. Modified cellulose-based filtration loss reducers have good salt resistance and can be used in saturated brine, and their biological stability is better than that of modified starch, but their temperature resistance can only reach 130℃. Modified lignite-based filtration loss reducers can withstand temperatures up to about 200℃, but are not salt resistant.

[0006] Therefore, given the current situation where drilling easily encounters formations containing polyvalent cations, and considering the scarcity of filtration loss reducers on the market that can simultaneously resist multiple cations, there is an urgent need to develop a filtration loss reducer that can resist polyvalent cations. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem of the lack of filtration loss reducers that can simultaneously resist multiple cations in the prior art, and to provide a new filtration loss reducer for drilling fluids that can simultaneously resist multiple cations.

[0008] To achieve the above objectives, the present invention provides a filtration loss reducer for drilling fluids, which includes structural unit A, structural unit B, structural unit C, and structural unit D.

[0009] The structural formula of structural unit A is:

[0010] The structural formula for structural unit B is:

[0011] The structural formula for structural unit C is:

[0012] The structural formula of structural unit D is:

[0013] Wherein, R1 is selected from C1-C5 alkylene groups, R2 and R3 are each independently selected from H and C1-C5 alkyl groups, and M is selected from H and alkali metals;

[0014] R4 is selected from C0-C5 alkylene groups, and R5 is selected from H and C1-C5 alkyl groups;

[0015] R6 is selected from H, C1-C5 alkyl groups, R7 is selected from H, C1-C5 alkyl groups, and R8 is selected from H, C1-C3 alkyl groups, and C6-C20 aryl groups;

[0016] R9, R 10 Each is independently selected from H, C1-C5 alkyl groups, R 11 X is selected from H, C1-C5 alkyl groups, and X is selected from halogens.

[0017] The second aspect of the present invention provides a method for preparing a filtration loss reducer for drilling fluids, the method comprising: subjecting monomers A, B, C, and D to solution free radical polymerization in the presence of an initiator and a solvent;

[0018] Wherein, monomer A is selected from monomers having the structure shown in formula (1);

[0019] Monomer B is selected from monomers having the structure shown in formula (2);

[0020] Monomer C is selected from monomers having the structure shown in formula (3);

[0021] Monomer D is selected from monomers having the structure shown in formula (4);

[0022] Wherein, R1 is selected from C1-C5 alkylene groups, R2 and R3 are each independently selected from H and C1-C5 alkyl groups, and M is selected from H and alkali metals;

[0023] R4 is selected from C0-C5 alkylene groups, and R5 is selected from H and C1-C5 alkyl groups;

[0024] R6 is selected from H, C1-C5 alkyl groups, R7 is selected from H, C1-C5 alkyl groups, and R8 is selected from H, C1-C3 alkyl groups, and C6-C20 aryl groups;

[0025] R9, R 10 Each is independently selected from H, C1-C5 alkyl groups, R 11 X is selected from H, C1-C5 alkyl groups, and X is selected from halogens.

[0026] A third aspect of the present invention provides a filtration loss reducer for drilling fluid prepared according to the preparation method provided by the present invention.

[0027] The fourth aspect of the present invention provides the application of the drilling fluid filtration reducer provided by the present invention in drilling fluid.

[0028] The drilling fluid filtration reducer provided by this invention is an anti-multivalent cationic supramolecular drilling fluid filtration reducer. Its molecular chain contains both anionic and cationic groups, exhibiting good aggregation stability and the ability to resist Ca2+ within a certain concentration range. 2+ Mg 2+ Al 3+ It can resist various cationic contaminants, maintain the filtration loss reduction capacity and rheological properties of water-based drilling fluid systems, and solve the problem of water-based drilling fluids resisting formation water with different salinity and saline formations.

[0029] The method for preparing drilling fluid filtration reducer provided by the present invention adopts a free radical solution polymerization method, which has a wide range of applicable monomers, easy control of polymerization temperature, and the filtration reducer product can exist stably in solution directly. The process is simple, the cost is low, and it is suitable for industrial application. Detailed Implementation

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] This invention provides a filtration loss reducer for drilling fluids, comprising structural unit A, structural unit B, structural unit C, and structural unit D.

[0032] The structural formula of structural unit A is:

[0033] The structural formula for structural unit B is:

[0034] The structural formula for structural unit C is:

[0035] The structural formula of structural unit D is:

[0036] Wherein, R1 is selected from C1-C5 alkylene groups, R2 and R3 are each independently selected from H and C1-C5 alkyl groups, and M is selected from H and alkali metals;

[0037] R4 is selected from C0-C5 alkylene groups, and R5 is selected from H and C1-C5 alkyl groups;

[0038] R6 is selected from H, C1-C5 alkyl groups, R7 is selected from H, C1-C5 alkyl groups, and R8 is selected from H, C1-C3 alkyl groups, and C6-C20 aryl groups;

[0039] R9, R 10 Each is independently selected from H, C1-C5 alkyl groups, R 11 X is selected from H, C1-C5 alkyl groups, and X is selected from halogens.

[0040] Any structural unit that meets the foregoing requirements can achieve the purpose of this invention. There are no special requirements for the specific selection of each group. The following is an illustrative description, but it does not limit the scope of this invention.

[0041] According to a preferred embodiment of the present invention, R1 is selected from -CH2-, -CH2CH2- or -CH2CH2CH2-, preferably -CH2-.

[0042] According to a preferred embodiment of the present invention, R2 and R3 are each independently selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably -CH3.

[0043] According to a preferred embodiment of the present invention, M is selected from H, Na or K, preferably H or Na.

[0044] According to a preferred embodiment of the present invention, R4 is selected from CO, -CH2-, -CH2CH2- or -CH2CH2CH2-, preferably CO or -CH2-, and R5 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably H.

[0045] According to a preferred embodiment of the present invention, R6 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, and is preferably H.

[0046] According to a preferred embodiment of the present invention, R7 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably -CH3.

[0047] According to a preferred embodiment of the present invention, R8 is selected from H, -CH3 or a benzene ring, preferably -CH3 or a benzene ring.

[0048] According to a preferred embodiment of the present invention, R9, R 10 Each is independently selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, with H being preferred.

[0049] According to a preferred embodiment of the present invention, R 11 It is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably -CH3.

[0050] According to a preferred embodiment of the present invention, X is selected from Cl, Br or I, preferably Cl or Br.

[0051] Specifically, the structural unit A can be selected from, for example, the structures shown in Equation (1-1), Equation (1-2), Equation (1-3), Equation (1-4), Equation (1-5), Equation (1-6), Equation (1-7), Equation (1-8), Equation (1-9), Equation (1-10), Equation (1-11), Equation (1-12), Equation (1-13), Equation (1-14), Equation (1-15), Equation (1-16), Equation (1-17), Equation (1-18), etc. The structural unit of the structure shown in (1-19), (1-20), (1-21), (1-22), (1-23), (1-24), (1-25), (1-26), (1-27), (1-28), (1-29), (1-30), (1-31), (1-32), (1-33), (1-34), (1-35), and (1-36) is one or more of the following:

[0052] in,

[0053] Equation (1-1): R1 is -CH3; R2 and R3 are H; M is H;

[0054] Equation (1-2): R1 is -CH3; R2 and R3 are H; M is K;

[0055] Equation (1-3): R1 is -CH3; R2 and R3 are H; M is Na;

[0056] Equation (1-4): R1 is -CH3; R2 and R3 are -CH3; M is H;

[0057] Equation (1-5): R1 is -CH3; R2 and R3 are -CH3; M is K;

[0058] Equation (1-6): R1 is -CH3; R2 and R3 are -CH3; M is Na;

[0059] Equation (1-7): R1 is -CH3; R2 and R3 are -CH2CH3; M is H;

[0060] Equation (1-8): R1 is -CH3; R2 and R3 are -CH2CH3; M is K;

[0061] Equation (1-9): R1 is -CH3; R2 and R3 are -CH2CH3; M is Na;

[0062] Equation (1-10): R1 is -CH3; R2 and R3 are -CH2CH2CH3; M is H;

[0063] Equation (1-11): R1 is -CH3; R2 and R3 are -CH2CH2CH3; M is K;

[0064] Equation (1-12): R1 is -CH3; R2 and R3 are -CH2CH2CH3; M is Na;

[0065] Equation (1-13): R1 is -CH2CH3; R2 and R3 are H; M is H;

[0066] Equation (1-14): R1 is -CH2CH3; R2 and R3 are H; M is K;

[0067] Equation (1-15): R1 is -CH2CH3; R2 and R3 are H; M is Na;

[0068] Equation (1-16): R1 is -CH2CH3; R2 and R3 are -CH3; M is H;

[0069] Equation (1-17): R1 is -CH2CH3; R2 and R3 are -CH3; M is K;

[0070] Equation (1-18): R1 is -CH2CH3; R2 and R3 are -CH3; M is Na;

[0071] Equation (1-19): R1 is -CH2CH3; R2 and R3 are -CH2CH3; M is H;

[0072] Equation (1-20): R1 is -CH2CH3; R2 and R3 are -CH2CH3; M is K;

[0073] Equation (1-21): R1 is -CH2CH3; R2 and R3 are -CH2CH3; M is Na;

[0074] Equation (1-22): R1 is -CH2CH3; R2 and R3 are -CH2CH2CH3; M is H;

[0075] Equation (1-23): R1 is -CH2CH3; R2 and R3 are -CH2CH2CH3; M is K;

[0076] Equation (1-24): R1 is -CH2CH3; R2 and R3 are -CH2CH2CH3; M is Na;

[0077] Equation (1-25): R1 is -CH2CH2CH3; R2 and R3 are H; M is H;

[0078] Equation (1-26): R1 is -CH2CH2CH3; R2 and R3 are H; M is K;

[0079] Equation (1-27): R1 is -CH2CH2CH3; R2 and R3 are H; M is Na;

[0080] Equation (1-28): R1 is -CH2CH2CH3; R2 and R3 are -CH3; M is H;

[0081] Equation (1-29): R1 is -CH2CH2CH3; R2 and R3 are -CH3; M is K;

[0082] Equation (1-30): R1 is -CH2CH2CH3; R2 and R3 are -CH3; M is Na;

[0083] Equation (1-31): R1 is -CH2CH2CH3; R2 and R3 are -CH2CH3; M is H;

[0084] Equation (1-32): R1 is -CH2CH2CH3; R2 and R3 are -CH2CH3; M is K;

[0085] Equation (1-33): R1 is -CH2CH2CH3; R2 and R3 are -CH2CH3; M is Na;

[0086] Equation (1-34): R1 is -CH2CH2CH3; R2 and R3 are -CH2CH2CH3; M is H;

[0087] Equation (1-35): R1 is -CH2CH2CH3; R2 and R3 are -CH2CH2CH3; M is K;

[0088] Equation (1-36): R1 is -CH2CH2CH3; R2 and R3 are -CH2CH2CH3; M is Na.

[0089] The structural unit B can be selected from one or more of the following structures: the structure shown in equation (2-1), the structure shown in equation (2-2), the structure shown in equation (2-3), the structure shown in equation (2-4), the structure shown in equation (2-5), the structure shown in equation (2-6), the structure shown in equation (2-7), the structure shown in equation (2-8), the structure shown in equation (2-9), the structure shown in equation (2-10), the structure shown in equation (2-11), the structure shown in equation (2-12), the structure shown in equation (2-13), the structure shown in equation (2-14), the structure shown in equation (2-15), and the structural unit shown in equation (2-16).

[0090] in,

[0091] Equation (2-1): R4 is C0; R5 is H;

[0092] Equation (2-2): R4 is C0; R5 is -CH3;

[0093] Equation (2-3): R4 is C0; R5 is -CH2CH3;

[0094] Equation (2-4): R4 is C0; R5 is -CH2CH2CH3;

[0095] Equation (2-5): R4 is -CH3; R5 is H;

[0096] Equation (2-6): R4 is -CH3; R5 is -CH3;

[0097] Equation (2-7): R4 is -CH3; R5 is -CH2CH3;

[0098] Equation (2-8): R4 is -CH3; R5 is -CH2CH2CH3;

[0099] Equation (2-9): R4 is -CH2CH3; R5 is H;

[0100] Equation (2-10): R4 is -CH2CH3; R5 is -CH3;

[0101] Equation (2-11): R4 is -CH2CH3; R5 is -CH2CH3;

[0102] Equation (2-12): R4 is -CH2CH3; R5 is -CH2CH2CH3;

[0103] Equation (2-13): R4 is -CH2CH2CH3; R5 is H;

[0104] Equation (2-14): R4 is -CH2CH2CH3; R5 is -CH3;

[0105] Equation (2-15): R4 is -CH2CH2CH3; R5 is -CH2CH3;

[0106] Equation (2-16): R4 is -CH2CH2CH3; R5 is -CH2CH2CH3.

[0107] The structural unit C can be selected from, for example, the structures shown in Equation (3-1), Equation (3-2), Equation (3-3), Equation (3-4), Equation (3-5), Equation (3-6), Equation (3-7), Equation (3-8), Equation (3-9), Equation (3-10), Equation (3-11), Equation (3-12), Equation (3-13), Equation (3-14), Equation (3-15), Equation (3-16), and Equation (3-17). The structure shown in equation (17), equation (3-18), equation (3-19), equation (3-20), equation (3-21), equation (3-22), equation (3-23), equation (3-24), equation (3-25), equation (3-26), equation (3-27), equation (3-28), equation (3-29), equation (3-30), equation (3-31), and equation (3-32) are structural units of one or more of the following:

[0108] in,

[0109] Equation (3-1): R6 is H; R7 is H; R8 is H;

[0110] Formula (3-2): R6 is H; R7 is H; R8 is a benzene ring;

[0111] Equation (3-3): R6 is H; R7 is -CH3; R8 is H;

[0112] Formula (3-4): R6 is H; R7 is -CH3; R8 is a benzene ring;

[0113] Equation (3-5): R6 is H; R7 is -CH2CH3; R8 is H;

[0114] Formula (3-6): R6 is H; R7 is -CH2CH3; R8 is a benzene ring;

[0115] Equation (3-7): R6 is H; R7 is -CH2CH2CH3; R8 is H;

[0116] Formula (3-8): R6 is H; R7 is -CH2CH2CH3; R8 is a benzene ring;

[0117] Equation (3-9): R6 is -CH3; R7 is H; R8 is H;

[0118] Formula (3-10): R6 is -CH3; R7 is H; R8 is a benzene ring;

[0119] Equation (3-11): R6 is -CH3; R7 is -CH3; R8 is H;

[0120] Formula (3-12): R6 is -CH3; R7 is -CH3; R8 is a benzene ring;

[0121] Equation (3-13): R6 is -CH3; R7 is -CH2CH3; R8 is H;

[0122] Formula (3-14): R6 is -CH3; R7 is -CH2CH3; R8 is a benzene ring;

[0123] Equation (3-15): R6 is -CH3; R7 is -CH2CH2CH3; R8 is H;

[0124] Formula (3-16): R6 is -CH3; R7 is -CH2CH2CH3; R8 is a benzene ring;

[0125] Equation (3-17): R6 is -CH2CH3; R7 is H; R8 is H;

[0126] Formula (3-18): R5 is -CH2CH3; R6 is H; R7 is a benzene ring;

[0127] Equation (3-19): R6 is -CH2CH3; R7 is -CH3; R8 is H;

[0128] Formula (3-20): R6 is -CH2CH3; R7 is -CH3; R8 is a benzene ring;

[0129] Equation (3-21): R6 is -CH2CH3; R7 is -CH2CH3; R8 is H;

[0130] Formula (3-22): R6 is -CH2CH3; R7 is -CH2CH3; R8 is a benzene ring;

[0131] Equation (3-23): R6 is -CH2CH3; R7 is -CH2CH2CH3; R8 is H;

[0132] Formula (3-24): R6 is -CH2CH3; R7 is -CH2CH2CH3; R8 is a benzene ring;

[0133] Equation (3-25): R6 is -CH2CH2CH3; R7 is H; R8 is H;

[0134] Formula (3-26): R6 is -CH2CH2CH3; R7 is H; R8 is a benzene ring;

[0135] Equation (3-27): R6 is -CH2CH2CH3; R7 is -CH3; R8 is H;

[0136] Formula (3-28): R6 is -CH2CH2CH3; R7 is -CH3; R8 is a benzene ring;

[0137] Equation (3-29): R6 is -CH2CH2CH3; R7 is -CH2CH3; R8 is H;

[0138] Formula (3-30): R6 is -CH2CH2CH3; R7 is -CH2CH3; R8 is a benzene ring;

[0139] Equation (3-31): R6 is -CH2CH2CH3; R7 is -CH2CH2CH3; R8 is H;

[0140] Formula (3-32): R6 is -CH2CH2CH3; R7 is -CH2CH2CH3; R8 is a benzene ring.

[0141] The structural unit D can be selected from, for example, the structures shown in Equation (4-1), Equation (4-2), Equation (4-3), Equation (4-4), Equation (4-5), Equation (4-6), Equation (4-7), Equation (4-8), Equation (4-9), Equation (4-10), Equation (4-11), Equation (4-12), Equation (4-13), Equation (4-14), Equation (4-15), Equation (4-16), Equation (4-17), Equation (4-18), Equation (4-19), Equation (4-20), Equation (4-21), Equation (4-22), Equation (4-23), Equation (4-24), and Equation (4-25). The structure shown in equation (4-25), equation (4-26), equation (4-27), equation (4-28), equation (4-29), equation (4-30), equation (4-31), equation (4-32), equation (4-33), equation (4-34), equation (4-35), equation (4-36), equation (4-37), equation (4-38), equation (4-39), equation (4-40), equation (4-41), equation (4-42), equation (4-43), equation (4-44), equation (4-45), equation (4-46), equation (4-47), and equation (4-48) are structural units of one or more of the following:

[0142] in,

[0143] Equation (4-1): R9 is H; R 10 For H; R 11 X is -CH3;

[0144] Equation (4-2): R9 is H; R 10 For H; R 11 X is -CH3; Br is Br.

[0145] Equation (4-3): R9 is H; R 10 For H; R 11 -CH3; X is I;

[0146] Equation (4-4): R9 is H; R 10 -CH3; R 11 X is -CH3;

[0147] Equation (4-5): R9 is H; R 10 -CH3; R11 X is -CH3; Br is Br.

[0148] Equation (4-6): R9 is H; R 10 -CH3; R 11 -CH3; X is I;

[0149] Equation (4-7): R9 is H; R 10 -CH2CH3; R 11 X is -CH3;

[0150] Equation (4-8): R9 is H; R 10 -CH2CH3; R 11 X is -CH3; Br is Br.

[0151] Equation (4-9): R9 is H; R 10 -CH2CH3; R 11 -CH3; X is I;

[0152] Equation (4-10): R9 is H; R 10 -CH2CH2CH3; R 11 X is -CH3;

[0153] Equation (4-11): R9 is H; R 10 -CH2CH2CH3; R 11 X is -CH3; Br is Br.

[0154] Equation (4-12): R9 is H; R 10 -CH2CH2CH3; R 11 -CH3; X is I;

[0155] Equation (4-13): R9 is -CH3; R 10 For H; R 11 X is -CH3;

[0156] Equation (4-14): R9 is -CH3; R 10 For H; R 11 X is -CH3; Br is Br.

[0157] Equation (4-15): R9 is -CH3; R 10 For H; R 11 -CH3; X is I;

[0158] Equation (4-16): R9 is -CH3; R 10 -CH3; R 11 X is -CH3;

[0159] Equation (4-17): R9 is -CH3; R 10 -CH3; R 11 X is -CH3; Br is Br.

[0160] Equation (4-18): R9 is -CH3; R 10 -CH3; R 11 -CH3; X is I;

[0161] Equation (4-19): R9 is -CH3; R 10 -CH2CH3; R 11 X is -CH3;

[0162] Equation (4-20): R9 is -CH3; R 10 -CH2CH3; R 11 X is -CH3; Br is Br.

[0163] Equation (4-21): R9 is -CH3; R 10 -CH2CH3; R 11 -CH3; X is I;

[0164] Equation (4-22): R9 is -CH3; R 10 -CH2CH2CH3; R 11 X is -CH3;

[0165] Equation (4-23): R9 is -CH3; R 10 -CH2CH2CH3; R 11 X is -CH3; Br is Br.

[0166] Equation (4-24): R9 is -CH3; R 10 -CH2CH2CH3; R 11 -CH3; X is I;

[0167] Equation (4-25): R9 is -CH2CH3; R 10 For H; R 11 X is -CH3;

[0168] Equation (4-26): R9 is -CH2CH3; R 10 For H; R 11 X is -CH3; Br is Br.

[0169] Equation (4-27): R9 is -CH2CH3; R 10 For H; R 11 -CH3; X is I;

[0170] Equation (4-28): R9 is -CH2CH3; R10 -CH3; R 11 X is -CH3;

[0171] Equation (4-29): R9 is -CH2CH3; R 10 -CH3; R 11 X is -CH3; Br is Br.

[0172] Equation (4-30): R9 is -CH2CH3; R 10 -CH3; R 11 -CH3; X is I;

[0173] Equation (4-31): R9 is -CH2CH3; R 10 -CH2CH3; R 11 X is -CH3;

[0174] Equation (4-32): R9 is -CH2CH3; R 10 -CH2CH3; R 11 X is -CH3; Br is Br.

[0175] Equation (4-33): R9 is -CH2CH3; R 10 -CH2CH3; R 11 -CH3; X is I;

[0176] Equation (4-34): R9 is -CH2CH3; R 10 -CH2CH2CH3; R 11 X is -CH3;

[0177] Equation (4-35): R9 is -CH2CH3; R 10 -CH2CH2CH3; R 11 X is -CH3; Br is Br.

[0178] Equation (4-36): R9 is -CH2CH3; R 10 -CH2CH2CH3; R 11 -CH3; X is I;

[0179] Equation (4-37): R9 is -CH2CH2CH3; R 10 For H; R 11 X is -CH3;

[0180] Equation (4-38): R9 is -CH2CH2CH3; R 10 For H; R 11 X is -CH3; Br is Br.

[0181] Equation (4-39): R9 is -CH2CH2CH3; R 10 For H; R 11 -CH3; X is I;

[0182] Equation (4-40): R9 is -CH2CH2CH3; R 10 -CH3; R 11 X is -CH3;

[0183] Equation (4-41): R9 is -CH2CH2CH3; R 10 -CH3; R 11 X is -CH3; Br is Br.

[0184] Equation (4-42): R9 is -CH2CH2CH3; R 10 -CH3; R 11 -CH3; X is I;

[0185] Equation (4-43): R9 is -CH2CH2CH3; R 10 -CH2CH3; R 11 X is -CH3;

[0186] Equation (4-44): R9 is -CH2CH2CH3; R 10 -CH2CH3; R 11 X is -CH3; Br is Br.

[0187] Equation (4-45): R9 is -CH2CH2CH3; R 10 -CH2CH3; R 11 -CH3; X is I;

[0188] Equation (4-46): R9 is -CH2CH2CH3; R 10 -CH2CH2CH3; R 11 X is -CH3;

[0189] Equation (4-47): R9 is -CH2CH2CH3; R 10 -CH2CH2CH3; R 11 X is -CH3; Br is Br.

[0190] Equation (4-48): R9 is -CH2CH2CH3; R 10 -CH2CH2CH3; R 11 X is -CH3; I is I.

[0191] All of the above structural formulas can achieve the purpose of the present invention. The advantages of the present invention are illustrated by example in the embodiments, but they should not be used to limit the scope of the present invention.

[0192] In this invention, the content of each structural unit in the drilling fluid filtration reducer can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, based on the weight of the filtration reducer, the content of structural unit A is 5-89.9% by weight, the content of structural unit B is 1-40% by weight, the content of structural unit C is 10-70% by weight, and the content of structural unit D is 10-55% by weight.

[0193] According to a preferred embodiment of the present invention, based on the weight of the filtration loss reducing agent, the content of structural unit A is 10-65% by weight, the content of structural unit B is 4-30% by weight, the content of structural unit C is 20-50% by weight, and the content of structural unit D is 15-40% by weight. Preferably, based on the weight of the filtration loss reducing agent, the content of structural unit A is 15-40% by weight, the content of structural unit B is 5-25% by weight, the content of structural unit C is 30-50% by weight, and the content of structural unit D is 15-30% by weight.

[0194] According to a preferred embodiment of the present invention, the number-average molecular weight of the filtration loss reducing agent is 14,000-18,000, and the weight-average molecular weight is 70,000-120,000. Preferably, the number-average molecular weight of the filtration loss reducing agent is 15,000-17,000, and the weight-average molecular weight is 90,000-110,000.

[0195] The aforementioned preferred filtration reducer contains both anionic and cationic groups in its molecular chain, exhibiting good aggregation stability and making it suitable for use as a filtration reducer in water-based drilling fluids. It is also resistant to Ca2+. 2+ Mg 2+ Al 3+ It can resist various cationic contaminants, maintain the filtration loss reduction and rheological properties of water-based drilling fluid systems, and solve the problem of water-based drilling fluids resisting formation water with different mineralization and saline formations.

[0196] All drilling fluid filtration reducers with the aforementioned characteristics can achieve the purpose of this invention. There are no special requirements for their preparation methods. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the preparation method of the drilling fluid filtration reducer includes: in the presence of an initiator and a solvent, monomers A, B, C, and D undergoing solution free radical polymerization.

[0197] Wherein, monomer A is selected from monomers having the structure shown in formula (1);

[0198] Monomer B is selected from monomers having the structure shown in formula (2);

[0199] Monomer C is selected from monomers having the structure shown in formula (3);

[0200] Monomer D is selected from monomers having the structure shown in formula (4);

[0201] In formula (1) to formula (4), each group is defined in the same way as the structural unit described in this invention.

[0202] According to a preferred embodiment of the present invention, R1 is selected from -CH2-, -CH2CH2- or -CH2CH2CH2-, preferably -CH2-.

[0203] According to a preferred embodiment of the present invention, R2 and R3 are each independently selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably -CH3.

[0204] According to a preferred embodiment of the present invention, M is selected from H, Na or K, preferably H or Na.

[0205] According to a preferred embodiment of the present invention, R4 is selected from CO, -CH2-, -CH2CH2- or -CH2CH2CH2-, preferably CO or -CH2-.

[0206] According to a preferred embodiment of the present invention, R5 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably H.

[0207] According to a preferred embodiment of the present invention, R6 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, and is preferably H.

[0208] According to a preferred embodiment of the present invention, R7 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably -CH3.

[0209] According to a preferred embodiment of the present invention, R8 is selected from H, -CH3 or a benzene ring, preferably -CH3 or a benzene ring.

[0210] According to a preferred embodiment of the present invention, R9, R 10 Each is independently selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, with H being preferred.

[0211] According to a preferred embodiment of the present invention, R 11It is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3, preferably -CH3.

[0212] According to a preferred embodiment of the present invention, X is selected from Cl, Br or I, preferably Cl or Br.

[0213] According to a preferred embodiment of the present invention, the method for preparing the drilling fluid filtration reducer includes:

[0214] (1) Dissolve monomers A, B, C and D in a solvent and mix them thoroughly to obtain a mixed solution;

[0215] (2) The mixed solution obtained in step (1) is stirred and heated to a constant temperature under a nitrogen atmosphere, and then an initiator is added to carry out a solution free radical polymerization reaction.

[0216] In this invention, the mass ratio of monomer A, monomer B, monomer C and monomer D can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of monomer A, monomer B, monomer C and monomer D is 1-5:0.5-3:2-8:1-6.

[0217] According to a preferred embodiment of the present invention, the mass ratio of monomer A, monomer B, monomer C and monomer D is 1-5:1-3:3-8:2-5.

[0218] In this invention, there are no special requirements for the type of solvent. Any solvent that can achieve the purpose of this invention can be used in this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the solvent is one or more of deionized water, ethanol and methanol, preferably deionized water.

[0219] In this invention, the weight ratio of the total monomer weight to the solvent can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the weight ratio of the total monomer weight to the solvent is 2-8:1-5, preferably 2-6:1-3, for example 2:1, 3:2, 2:3, 4:3, 5:2.

[0220] In this invention, there are no special requirements for the type of initiator. Any initiator that can achieve the purpose of this invention can be used in this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the initiator is one or more of the following: haloalkanes, azobisisobutyronitrile (AIBN), 2-ketoglutaric acid, potassium persulfate, cerium ammonium nitrate, or azobisisobutyramidine hydrochloride (V50), preferably potassium persulfate.

[0221] In this invention, the weight ratio of the initiator to the total amount of monomer can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the weight ratio of the initiator to the total amount of monomer is 1-5:1000, preferably 2-4:1000, for example 2.5:1000, 3:1000, 3.5:1000.

[0222] In this invention, there are no special requirements for the containers used for the dissolution and polymerization reactions. Any container that can meet the requirements of this invention can be used in this invention. For example, monomers A, B, C, and D can be dissolved in a solvent in a beaker, and the polymerization reaction can be carried out in a three-necked flask equipped with a thermometer, a constant speed stirrer, and a reflux condenser.

[0223] In this invention, there are many possible methods for creating a nitrogen atmosphere. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the nitrogen atmosphere can be obtained by passing nitrogen gas through a three-necked flask for 10-20 minutes to remove oxygen from the container.

[0224] In this invention, there are no special requirements for the heating and heat preservation instruments used in the polymerization reaction. Any instrument that can meet the requirements of this invention can be used in this invention, such as a constant temperature water bath.

[0225] In embodiments of the present invention, monomer A is selected from 2-acrylamido-2-methylpropanesulfonic acid and / or sodium 2-acrylamido-2-methylpropanesulfonate, whose molecular structure contains unsaturated carbon-carbon double bonds, facilitating copolymerization with other monomers. The synthesized filtration loss reducer has sulfonic acid groups with good temperature and salt resistance added to its molecular chain, giving it greater rigidity and enhancing the copolymer's resistance to high temperatures and salt, thereby improving the temperature and salt resistance of the filtration loss reducer.

[0226] In embodiments of the present invention, monomer B is selected from N-vinyl-2-pyrrolidone and / or 1-allyl-2-pyrrolidone, which has a rigid pyrrolidine ring in its molecular structure. Such cyclic substances can increase the rotational energy of polymer bonds, effectively improving the spreadability of the filtration loss reducer in aqueous solution. The higher spreadability enhances the rigidity of the copolymer molecular chain. For example, N-vinyl-2-pyrrolidone is used as an example to explain its advantages. Normally, the hydrolysis of phthalamide groups on the molecular chain is the main reason for the decrease in the temperature and salt resistance of the copolymer filtration loss reducer. However, the pyrrolidine ring on N-vinyl-2-pyrrolidone can inhibit its hydrolysis, allowing the copolymer to maintain its good stability in a high-temperature, salty, calcium-containing environment. As can be seen from the structural formula of N-vinyl-2-pyrrolidone, there is a propionamide group in the five-membered heterocyclic structure. The propionamide group has extremely high polarity, and the nitrogen atom is surrounded by a methyl group and a methylene group. This structure determines that such a five-membered ring structure is not easily degraded at high temperatures, further increasing its high-temperature stability.

[0227] In embodiments of the present invention, monomer C is selected from tetramethyldivinyldisiloxane and / or dimethyldiphenyldivinyldisiloxane, whose molecular structure contains two vinyl functional groups and two or more methyl functional groups. The vinyl functional groups endow the compound with double bond characteristics, while the methyl functional groups increase the compound's hydrophobicity. The reason for choosing tetramethyldivinyldisiloxane or dimethyldiphenyldivinyldisiloxane as one of the monomers to develop the salt-resistant and calcium-resistant filtration-reducing agent is mainly due to their hydrophobicity and the properties of silane compounds. Because of their hydrophobicity, these compounds can form a hydrophobic film in water, thereby preventing the precipitation and crystallization of salt and calcium ions. Furthermore, silane compounds can also react chemically with salt and calcium ions to form insoluble precipitates, thereby reducing the salt and calcium content.

[0228] In embodiments of the present invention, monomer D is selected from dimethyldiammonium chloride-based acrylamide and / or dimethyldibromide-based acrylamide. This is a cationic monomer containing dimethyldiammonium chloride and acrylamide functional groups. Its cationic functional groups can form ionic bonds with anions in water, thereby forming a protective cationic membrane in water. This membrane can prevent the precipitation and crystallization of salt and calcium ions, reducing the erosion and damage of drilling fluid by salt and calcium. The acrylamide functional groups can undergo cross-linking reactions with other functional groups to form a three-dimensional network structure. By designing and selecting reactions with acrylamide functional groups, the performance of the filtration loss reducer can be regulated and improved, enhancing its resistance to salt and temperature.

[0229] In this invention, there are no special requirements for the free radical polymerization reaction temperature. Commonly used polymerization reaction temperatures are applicable to this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the polymerization reaction temperature is 40-90°C, preferably 65-70°C.

[0230] In this invention, the solution free radical polymerization reaction is carried out under conditions with a pH value of 6-9. In this invention, different monomers A, B, C, and D dissolved in the solvent will form solutions with different pH values. Sometimes it is necessary to add a pH adjuster to the solution to bring the pH value within the range of 6-9. The pH adjuster can be any conventional pH adjuster in the art, such as one or more of sodium hydroxide, sodium carbonate, potassium carbonate, and ammonia water, preferably sodium hydroxide.

[0231] In this invention, the free radical polymerization reaction pressure can be selected from a wide range, and commonly used polymerization reaction pressures are all applicable to this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the polymerization reaction pressure is 0.01-1 MPa, preferably atmospheric pressure.

[0232] In this invention, the polymerization reaction time can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the polymerization reaction time is 3-6 hours, preferably 5-5.5 hours.

[0233] In this invention, there are no special requirements for the stirring speed. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the stirring speed is 200-800 rpm, preferably 300-600 rpm. The method for preparing the drilling fluid filtration reducer provided by this invention adopts a free radical solution polymerization method, which has a wide range of applicable monomers, easy control of polymerization temperature, and the filtration reducer product can exist stably directly in solution. The process is simple, the cost is low, and it is suitable for industrial application.

[0234] This invention provides a filtration loss reducer for drilling fluids prepared according to the preparation method of this invention. The filtration loss reducer's molecular chain contains both anionic and cationic groups, exhibiting good aggregation stability and resistance to Ca2+. 2+ Mg 2+ Al 3+ It can resist various cationic contaminants, maintain the filtration loss reduction and rheological properties of water-based drilling fluid systems, and solve the problem of water-based drilling fluids resisting formation water with different mineralization and saline formations.

[0235] This invention provides the application of the drilling fluid filtration reducer described herein in drilling fluids.

[0236] In this invention, the number-average molecular weight and weight-average molecular weight of the filtration reduction agent were determined by gel permeation chromatography (GPC). The instrument model was Waters e2695. The column temperature was 35℃, the mobile phase was tetrahydrofuran (THF), and the flow rate was 1 ml / min. Polystyrene was used as a standard.

[0237] In this invention, a 1103 type six-speed rotational viscometer was used to characterize the apparent viscosity, plastic viscosity, and dynamic shear force of various water-based drilling fluids containing filtration loss reducers. Referring to standard GB / T 16782-1997, the values ​​of Φ600 and Φ300, as well as the value of Φ3 after stirring at 600 rpm for 1 min and then standing for 10 s and 10 min respectively, were measured using a six-speed rotational viscometer. The apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the water-based drilling fluid were calculated using the following formulas.

[0238] (1) Apparent viscosity AV (unit mPa·s) = 0.50 * Φ600

[0239] (2) Plastic viscosity PV (unit mPa·s) = Φ600 - Φ300

[0240] (3) Dynamic shear force (unit Pa) YP=0.511*(Φ300-PV)

[0241] (4) Initial tangent (τinitial) = 0.511 * Φ3 (after standing for 10 seconds)

[0242] Final cut (τfinal) = 0.511 * Φ3 (after standing for 10 min)

[0243] Test method for medium-pressure filtration loss: Add metal salts of different concentrations and valence states to the prepared base slurry, and stir with a high-speed mixer at a drilling speed of 12000 rpm for 20 minutes. Then, pour 150 mL of contaminated drilling fluid into a medium-pressure filtration loss meter, place the gasket and special filter paper, and tighten the cap. Record the filtrate volume over 30 minutes at an output pressure of 0.69 MPa. This is the medium-pressure API filtration loss of the drilling fluid before aging. Alternatively, take 300 mL of contaminated drilling fluid, age it at 150℃ for 16 hours, and then pour 150 mL of the aged drilling fluid into a medium-pressure filtration loss meter. Place the gasket and special filter paper, tighten the cap, and record the filtrate volume over 30 minutes at an output pressure of 0.69 MPa. This is the medium-pressure API filtration loss of the drilling fluid after aging.

[0244] The examples illustrate the drilling fluid filtration reducer with anti-multivalent cation function of the present invention and its preparation method.

[0245] Example 1

[0246] In a beaker, 200g of monomers A1, B1, C1, and D1 in a weight ratio of 3:1:5:2 were dissolved in 130g of deionized water. The mixture was stirred at 500rpm, and 20wt% NaOH aqueous solution was added to adjust the pH of the system to 7. After the solution was thoroughly mixed, it was poured into a three-necked flask and stirred at 500rpm. Nitrogen gas was purged for 10min to remove oxygen from the container. 10mL of an aqueous solution of potassium persulfate (0.3% of the total monomer weight) was added at a uniform rate of 1mL / s. The mixture was heated to 65℃ in a constant temperature water bath and reacted for 5h. The synthesized product was the filtration loss reducer W1. GPC analysis showed that the number average molecular weight of filtration loss reducer W1 was 16279, and the weight average molecular weight was 108691.

[0247] Example 2

[0248] In a beaker, 200g of monomers A1, B1, C1, and D1 in a weight ratio of 2:2:4:3 were dissolved in 130g of deionized water. The mixture was stirred at 500rpm, and 20wt% NaOH aqueous solution was added to adjust the pH of the system to 7. After the solution was thoroughly mixed, it was poured into a three-necked flask and stirred at 500rpm. Nitrogen gas was purged for 10min to remove oxygen from the container. 10mL of a potassium persulfate aqueous solution (0.3% of the total monomer weight) was added at a constant rate of 1mL / s. The mixture was heated to 65℃ in a constant temperature water bath and reacted for 5h. The synthesized product was the filtration loss reducer W2. GPC analysis showed that the number average molecular weight of filtration loss reducer W2 was 16854, and the weight average molecular weight was 108902.

[0249] Example 3

[0250] In a beaker, 200 g of monomers A1, B1, C1, and D1 in a weight ratio of 4:2:4:2 were dissolved in 130 g of deionized water. The mixture was stirred at 500 rpm, and 20 wt% NaOH aqueous solution was added to adjust the pH of the system to 7. After the solution was thoroughly mixed, it was poured into a three-necked flask and stirred at 500 rpm. Nitrogen gas was purged for 10 min to remove oxygen from the container. 10 mL of an aqueous solution of potassium persulfate (0.3% of the total monomer weight) was added at a uniform rate of 1 mL / s. The mixture was heated to 65 °C in a constant temperature water bath and reacted for 5 h. The synthesized product was the filtration loss reducer W3. GPC analysis showed that the number average molecular weight of filtration loss reducer W3 was 15780, and the weight average molecular weight was 94662.

[0251] Example 4

[0252] In a beaker, 200g of monomers A2, B1, C1, and D2 in a weight ratio of 3:1:5:2 were dissolved in 130g of deionized water. The mixture was stirred at 500rpm until homogeneous. The solution was then poured into a three-necked flask and stirred at 500rpm. Nitrogen gas was purged for 10 minutes to remove oxygen. 10mL of a potassium persulfate aqueous solution (0.3% of the total monomer weight) was added at a constant rate of 1mL / s. The mixture was heated to 65℃ in a constant temperature water bath and reacted for 5 hours. The synthesized product was the filtration loss reducer W4. GPC analysis showed that the number-average molecular weight of filtration loss reducer W4 was 16381, and the weight-average molecular weight was 108715.

[0253] Example 5

[0254] In a beaker, 200g of monomers A2, B1, C1, and D2 in a weight ratio of 2:2:4:3 were dissolved in 130g of deionized water. The mixture was stirred at 500rpm until homogeneous. The solution was then poured into a three-necked flask and stirred at 500rpm. Nitrogen gas was purged for 10 minutes to remove oxygen. 10mL of a potassium persulfate aqueous solution (0.3% of the total monomer weight) was added at a constant rate of 1mL / s. The mixture was heated to 65℃ in a constant temperature water bath and reacted for 5 hours. The synthesized product was the filtration loss reducer W5. GPC analysis showed that the number-average molecular weight of filtration loss reducer W5 was 16924, and the weight-average molecular weight was 108970.

[0255] Example 6

[0256] In a beaker, 200g of monomers A2, B1, C1, and D2 in a weight ratio of 4:2:4:2 were dissolved in 130g of deionized water. The mixture was stirred at 500rpm until homogeneous. The solution was then poured into a three-necked flask and stirred at 500rpm. Nitrogen gas was purged for 10 minutes to remove oxygen. 10mL of a 0.3% potassium persulfate aqueous solution (based on the raw material weight ratio) was added at a uniform rate of 1mL / s. The mixture was heated to 65℃ in a constant-temperature water bath and reacted for 5 hours. The synthesized product was the filtration loss reducer W6. GPC analysis revealed that the number-average molecular weight of filtration loss reducer W6 was 15791, and the weight-average molecular weight was 94673.

[0257] Example 7

[0258] In a beaker, 200 g of monomers A2, B2, C2, and D2 in a weight ratio of 3:1:5:2 were dissolved in 130 g of deionized water. The mixture was stirred at 500 rpm until homogeneous. The solution was then poured into a three-necked flask and stirred at 500 rpm. Nitrogen gas was purged for 10 min to remove oxygen. 10 mL of a potassium persulfate aqueous solution (0.3% of the total monomer weight) was added at a constant rate of 1 mL / s. The mixture was heated to 65 °C in a constant temperature water bath and reacted for 5 h. The synthesized product was the filtration loss reducer W7. GPC analysis showed that the number average molecular weight of filtration loss reducer W7 was 15763, and the weight average molecular weight was 98625.

[0259] Example 8

[0260] In a beaker, 200g of monomers A2, B2, C2, and D2 in a weight ratio of 2:2:4:3 were dissolved in 130g of deionized water. The mixture was stirred at 500rpm until homogeneous. The solution was then poured into a three-necked flask and stirred at 500rpm. Nitrogen gas was purged for 10 minutes to remove oxygen. 10mL of a potassium persulfate aqueous solution (0.3% of the total monomer weight) was added at a constant rate of 1mL / s. The mixture was heated to 65℃ in a constant temperature water bath and reacted for 5 hours. The synthesized product was the filtration loss reducer W8. GPC analysis showed that the number-average molecular weight of filtration loss reducer W8 was 16127, and the weight-average molecular weight was 100416.

[0261] Example 9

[0262] In a beaker, 200 g of monomers A2, B2, C2, and D2 in a weight ratio of 4:2:4:2 were dissolved in 130 g of deionized water. The mixture was stirred at 500 rpm until homogeneous. The solution was then poured into a three-necked flask and stirred at 500 rpm. Nitrogen gas was purged for 10 min to remove oxygen. 10 mL of a potassium persulfate aqueous solution (0.3% of the raw materials by weight) was added at a uniform rate of 1 mL / s. The mixture was heated to 65 °C in a constant temperature water bath and reacted for 5 h. The synthesized product was the filtration loss reducer W9. GPC analysis showed that the number average molecular weight of filtration loss reducer W9 was 15987, and the weight average molecular weight was 99765.

[0263] Comparative Example 1

[0264] The method of Example 1 was followed, except that the monomer raw materials were monomers A1, C1, and D1 in a weight ratio of (3:5:2). The synthesized product was the filtration loss reducer DW1. The number average molecular weight of filtration loss reducer DW1 was 16725 and the weight average molecular weight was 11243 as determined by GPC.

[0265] Comparative Example 2

[0266] The method of Example 1 was followed, except that the monomer raw materials were monomers A1, B1, and D1 in a weight ratio of (3:1:2). The synthesized product was the filtration loss reducer DW2. The number average molecular weight of filtration loss reducer DW1 was 13143 and the weight average molecular weight was 88240 as determined by GPC.

[0267] Test Example 1

[0268] Following the above method, the prepared filtration loss reducer was subjected to single-agent performance tests at different temperatures.

[0269] The filtration loss reducer prepared according to this invention was added to a water-based drilling fluid system formulated with 4 wt% sodium-based slurry, wherein the amount of filtration loss reducer added was 2% of the drilling fluid mass. The filtration loss and basic properties such as rheology of each water-based drilling fluid containing the synthesized filtration loss reducer were tested. The results of apparent viscosity (AV / mPa·s), plastic viscosity (PV / mPa·s), dynamic shear force (YP / Pa), and medium-pressure filtration loss (API / mL) of the above drilling fluids are shown in Table 1.

[0270] Table 1. Effects of Filtration Loss Reducers on Drilling Fluid Properties

[0271] As can be seen from the data in Table 1, the test results show that the filtration loss reducer provided by the present invention has a significant improvement on the filtration loss reduction performance of drilling fluid and can play a regulatory role in the rheological properties of drilling fluid. The filtration loss reducers with different structures prepared have different degrees of influence on drilling fluid.

[0272] Test Example 2

[0273] The filtration loss reducer prepared according to this invention was added to a water-based drilling fluid system prepared with 4 wt% sodium-based slurry. Then, 30 wt% NaCl was added to contaminate the drilling fluid. The amount of filtration loss reducer added was 2 wt% of the drilling fluid mass. The filtration loss and basic properties such as rheology of each water-based drilling fluid containing the synthesized filtration loss reducer were tested. The apparent viscosity (AV / mPa·s), plastic viscosity (PV / mPa·s), dynamic shear force (YP / Pa), and medium-pressure filtration loss (API / mL) of the above drilling fluids are shown in Table 2.

[0274] Table 2. Effects of filtration loss reducers on drilling fluid properties after 30% NaCl contamination.

[0275] As can be seen from the data in Table 2, the test results show that the drilling fluid system with the filtration loss reducer provided by this invention has good anti-fouling performance against NaCl.

[0276] Test Example 3

[0277] The filtration loss reducer prepared according to this invention was added to a water-based drilling fluid system prepared with 4 wt% sodium-based slurry. Then, 30 wt% KCl was added to the drilling fluid to contaminate it. The amount of filtration loss reducer added was 2 wt%. The filtration loss and basic properties such as rheology of each water-based drilling fluid containing the synthesized filtration loss reducer were tested. The apparent viscosity (AV / mPa·s), plastic viscosity (PV / mPa·s), dynamic shear force (YP / Pa), and medium-pressure filtration loss (API / mL) of the above drilling fluids are shown in Table 3.

[0278] Table 3. Effects of filtration loss reducers on drilling fluid properties after 30% KCl contamination.

[0279] As can be seen from the data in Table 3, the test results show that the drilling fluid system with the filtration loss reducer provided by this invention has good anti-fouling performance against KCl.

[0280] Test Example 4

[0281] The filtration loss reducer prepared according to this invention was added to a water-based drilling fluid system prepared with 4 wt% sodium-based slurry. Then, 5 wt% CaCl2 was added to the drilling fluid to contaminate it. The amount of filtration loss reducer added was 2 wt%. The filtration loss and basic properties such as rheology of each water-based drilling fluid containing the synthesized filtration loss reducer were tested. The apparent viscosity (AV / mPa·s), plastic viscosity (PV / mPa·s), dynamic shear force (YP / Pa), and medium-pressure filtration loss (API / mL) of the above drilling fluids are shown in Table 4.

[0282] Table 4. Effects of filtration loss reducers on drilling fluid properties after 5% CaCl2 contamination.

[0283] As can be seen from the data in Table 4, the test results show that the drilling fluid system with the filtration loss reducer provided by this invention has good anti-fouling performance against CaCl2.

[0284] Test Example 5

[0285] The filtration loss reducer prepared according to this invention was added to a water-based drilling fluid system prepared with 4 wt% sodium-based slurry. Then, 5 wt% MgCl2 was added to the drilling fluid to contaminate it. The amount of filtration loss reducer added was 2 wt%. The filtration loss and basic properties such as rheology of each water-based drilling fluid containing the synthesized filtration loss reducer were tested. The apparent viscosity (AV / mPa·s), plastic viscosity (PV / mPa·s), dynamic shear force (YP / Pa), and medium-pressure filtration loss (API / mL) of the above drilling fluids are shown in Table 5.

[0286] Table 5. Effects of filtration loss reducers on drilling fluid properties after 5% MgCl2 contamination.

[0287] As can be seen from the data in Table 5, the test results show that the drilling fluid system with the filtration loss reducer provided by this invention has good anti-fouling performance against MgCl2.

[0288] Test Example 6

[0289] The filtration loss reducer prepared according to this invention was added to a water-based drilling fluid system prepared with 4 wt% sodium-based slurry. Then, 0.5 wt% AlCl3 was added to contaminate the drilling fluid. The amount of filtration loss reducer added was 2 wt%. The filtration loss and basic properties such as rheology of the water-based drilling fluids containing the synthesized filtration loss reducer were tested. The apparent viscosity (AV / mPa·s), plastic viscosity (PV / mPa·s), dynamic shear force (YP / Pa), and medium-pressure filtration loss (API / mL) of the above drilling fluids are shown in Table 6.

[0290] Table 6. Effects of filtration loss reducers on drilling fluid properties after 0.5% AlCl3 contamination.

[0291] As can be seen from the data in Table 6, the test results show that the drilling fluid system with the filtration loss reducer provided by this invention has good anti-fouling performance against AlCl3.

[0292] Based on the data results in Tables 1-6, it can be concluded that the drilling fluid filtration reducer provided by this invention, as an anti-multivalent cation filtration reducer, can improve the viscosity of the drilling fluid, significantly reduce filtration loss, and has good anti-pollution performance against cations of various valence states. It can reduce the filtration loss of drilling fluid during drilling operations and provide a guarantee for the safety of drilling operations.

[0293] In summary, the drilling fluid filtration reducer provided by this invention has a very significant effect on water-based drilling fluids resisting multivalent cation filtration reduction. It can greatly improve the rheological properties and filtration loss of the drilling fluid, enhance the anti-fouling performance of the drilling fluid, and the preparation method is simple and low in cost. Therefore, this invention has a very broad application prospect and can effectively solve the problems of wellbore instability and reservoir contamination caused by excessive filtration loss in drilling operations, reduce the occurrence of complex downhole accidents, and bring about improved economic benefits.

[0294] The preferred embodiments of the present invention have been described above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A filtrate reducer for drilling fluids, characterized by, The filtrate reducer comprises a structural unit A, a structural unit B, a structural unit C and a structural unit D, The structural formula of the structural unit A is: The structural formula of the structural unit B is: The structural formula of the structural unit C is: The structural formula of the structural unit D is: wherein R1 is selected from C1-C5 alkylene, R2 and R3 are each independently selected from H and C1-C5 alkyl, and M is selected from H and alkali metal; R4 is selected from C0-C5 alkylene, and R5 is selected from H and C1-C5 alkyl; R6 is selected from H and C1-C5 alkyl, R7 is selected from H and C1-C5 alkyl, and R8 is selected from H, C1-C3 alkyl and C6-C20 aryl; R9, R 10 each independently selected from H, C1-C5 alkyl, R 11 selected from H, C1-C5 alkyl, X is selected from halogen.

2. The filtrate reducer according to claim 1, wherein R1 is selected from -CH2-, -CH2CH2- or -CH2CH2CH2-; and / or R2 and R3 are each independently selected from H, -CH3, -CH2CH3 or -CH2CH2CH3; and / or M is selected from H, Na or K; and / or R4 is selected from C0-C3 alkylene; and / or R5 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3; and / or R6 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3; and / or R7 is selected from H, -CH3, -CH2CH3 or -CH2CH2CH3; and / or R8 is selected from H, -CH3 or phenyl; and / or X is selected from Cl, Br or I.

3. The filtrate reducer according to claim 1, wherein the content of the structural unit A is 5-89.9% by weight, the content of the structural unit B is 1-40% by weight, the content of the structural unit C is 10-70% by weight, and the content of the structural unit D is 10-55% by weight, based on the weight of the filtrate reducer; and / or the number average molecular weight of the filtrate reducer is 14000-18000, and the weight average molecular weight is 70000-120000.

4. The filtrate reducer according to claim 3, wherein the content of the structural unit A is 10-65% by weight, the content of the structural unit B is 4-30% by weight, the content of the structural unit C is 20-50% by weight, and the content of the structural unit D is 15-40% by weight, based on the weight of the filtrate reducer; and / or the number average molecular weight of the filtrate reducer is 15000-17000, and the weight average molecular weight is 90000-110000.

5. The filtrate reducer according to any one of claims 1-4, wherein the content of the structural unit A is 15-40% by weight, the content of the structural unit B is 5-25% by weight, the content of the structural unit C is 30-50% by weight, and the content of the structural unit D is 15-30% by weight, based on the weight of the filtrate reducer. The method comprises: under the presence of an initiator and a solvent, subjecting monomer A, monomer B, monomer C and monomer D to solution radical polymerization; in formula (1)-formula (4), each group is the same as the definition in each structural unit in any one of claims 1-5. The method comprises: (1) dissolving monomer A, monomer B, monomer C and monomer D in a solvent, and uniformly mixing to obtain a mixed solution; R9, R 10 each independently selected from H, -CH3, -CH2CH3, or -CH2CH2CH3; and / or R 11 is selected from H, -CH3, -CH2CH3, or -CH2CH2CH3; and / or ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 6. A method for preparing a filtrate reducer for a drilling fluid, characterized by, ​ ​ wherein monomer A is selected from monomers having the structure shown in formula (1); Monomer B is selected from monomers having the structure shown in formula (2); Monomers C are selected from monomers having the structure according to Formula (3); Monomers D are selected from monomers having the structure of Formula (4); ​ 7. The production method according to claim 6, wherein ​ ​ (2) The mixed solution obtained in step (1) is stirred under a nitrogen atmosphere and heated to a constant temperature, and then an initiator is added to perform solution radical polymerization.

8. The production method according to claim 6 or 7, characterized by, The mass ratio of monomer A, monomer B, monomer C and monomer D is 1-5:0.5-3:2-8:1-6.

9. The production method according to claim 6 or 7, characterized by, The mass ratio of monomer A, monomer B, monomer C and monomer D is 1-5:1-3:3-8:2-5.

10. The preparation method of claim 6 or 7, wherein, the solvent is one or more of deionized water, ethanol and methanol; and / or The weight ratio of the total weight of monomers to the solvent is 2-8:1-5.

11. The preparation method of claim 6 or 7, wherein, the initiator is selected from one or more of halogenated alkane, azobisisobutyronitrile, 2-ketoglutaric acid, potassium persulfate, cerium ammonium nitrate or azobis isobutyrimidamide hydrochloride; and / or The weight ratio of the initiator to the total amount of monomers is 1-5:1000.

12. The production method according to claim 6 or 7, characterized by, The solution radical polymerization reaction conditions include: the temperature is 40-90℃; and / or the solution pH is 6-9; and / or the pressure is 0.01-1 MPa; and / or the time is 3-6h; and / or the stirring speed is 200-800rpm.

13. The fluid loss additive for drilling fluid prepared by the preparation method of any one of claims 6-12.

14. The use of the fluid loss additive for drilling fluid of any one of claims 1-5 and 13 in drilling fluid.

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