Chemically bonded lost circulation additive, composite lost circulation additive comprising same, drilling fluid, and use thereof in drilling engineering

Abstract

The present disclosure provides a chemical bonding lost circulation additive, a composite lost circulation additive comprising same, a drilling fluid, and a use thereof in drilling engineering. The chemical bonding lost circulation additive comprises a core layer and an inorganic material coating the outer surface of the core layer, wherein the material of the core layer has a structure as shown in formula (I). The lost circulation additive of the present application demonstrates a higher one-time plugging success rate, better pressure-bearing capacity, better compatibility with a drilling fluid, stronger temperature resistance, stronger contamination resistance, and stronger salt tolerance.(I)

Description

CHEMICALLY BONDED LOST CIRCULATION ADDITIVE, COMPOSITE LOST CIRCULATION ADDITIVE COMPRISING SAME, DRILLING FLUID, AND USE THEREOF IN DRILLING ENGINEERING CROSS-REFERENCE TO RELATED APPLICATIONS[1] The present application claims the priority to Chinese Patent Application No. 202311791338.9, filed with the China National Intellectual Property Administration on December 22, 2023 and entitled "LOST CIRCULATION ADDITIVE, COMPOSITE LOST CIRCULATION ADDITIVE COMPRISING SAME, DRILLING FLUID, AND USE THEREOF IN DRILLING ENGINEERING", which is incorporated herein by reference in its entirety. TECHNICAL FIELD[2] The present disclosure belongs to the technical field of the development of oil field chemicals, and more particularly relates to a chemical bonding lost circulation additive, a composite lost circulation additive comprising same, a drilling fluid, and use thereof in drilling engineering. BACKGROUND ART[3] Lost circulation of drilling fluids is a worldwide technical challenge in drilling engineering. At present, bridging lost circulation materials are the most commonly used on-site lost circulation additives. Bridging lost circulation materials include granular, flaky, and fibrous nut shells, calcium carbonate, fibers, mica, etc., and rely on bridging with large particles and filling and plugging with small particles to prevent lost circulation of drilling fluids. However, plugging by physical accumulation alone results in weak pressure resistance and a low success rate of one-time plugging. SUMMARY OF THE INVENTION[4] In order to improve the above-mentioned problems, according to an aspect of the present disclosure, a chemical bonding lost circulation additive is provided, which comprises a core layer and an inorganic material coating the outer surface of the core layer, wherein the material of the core layer has a structure as shown in formula I:formula Iwherein in formula Ⅰ, represents ; and the number-average molecular weight of the material of the core layer is 20000-35000, and the values of m and n can satisfy the range of the number-average molecular weight of the material of the core layer. Without particular limitation, m represents 10-14, and n represents 12-20, for example.[5] Firstly, the material of the core layer in the lost circulation additive of the present disclosure has a strong chemical bonding effect. In subsequent plugging applications, the inorganic material in the lost circulation additive is dispersed in a drilling fluid (whether an oil-based drilling fluid or a water-based drilling fluid, to which the additive is added and in which it can be dispersed due to the viscosity of the drilling fluid) during subsequent application, so that the materials of the core layer are exposed and come into contact with each other and chemical bonding occurs under high-temperature (≥ 50°C) and compressive conditions in the formation to form an integral gel; therefore, a plugging layer having higher strength, better pressure-bearing capacity and superior toughness can be obtained more efficiently. The principle of the chemical bonding described above is as follows:[6] On this basis, the present disclosure can not only greatly increase the plugging success rate, optimize the plugging efficiency, and overcome the problem of a low one-time plugging success rate caused by sole reliance on physical accumulation in traditional bridging lost circulation additives; in addition, it also improves the pressure-bearing capacity of a plugging system and overcomes the disadvantage of weak pressure-bearing capacity caused by the sole reliance on physical accumulation in traditional bridging lost circulation additives. Moreover, the above-mentioned lost circulation additive of the present disclosure also has the following excellent properties: relatively good high-temperature resistance and sustained stable performance in high-temperature downhole operations; good compatibility with drilling fluids (good compatibility with all water-based and oil-based drilling fluid systems on the market) and superior application; relatively strong contamination resistance; and relatively strong salt resistance.[7] Secondly, the outer surface of the material of the core layer in the lost circulation additive of the present disclosure is coated with the inorganic material, thereby effectively preventing the material of the core layer from bonding during storage and transportation and better facilitating storage and transportation. During on-site construction, the lost circulation additive can be directly prepared in a fluid formulation tank without the need for batching skid-mounted equipment, has easy and convenient construction, requires less equipment investment, low labor intensity, low overall costs, and is convenient for large-scale promotion and application. The lost circulation additive has better prospects for industrial application. Furthermore, the inorganic material can be dispersed in the drilling fluid during subsequent plugging application, so that the materials of the core layer are exposed and come into contact with each other.[8] Furthermore, the weight ratio of the inorganic material to the core layer is 2-4 : 1; and preferably, the weight ratio of the inorganic material to the core layer is 2-3 : 1. The inorganic material is selected from one or more of calcium carbonate, magnesium carbonate, bentonite, or talc powder. In an alternative embodiment, the material of the core layer and the inorganic material are mixed and stirred such that the inorganic material coats (physically coats) the outer surface of the core layer.[9] In a preferred embodiment, the material of the core layer is granular and has a particle size of 8-40 mesh (for example, 8-10 mesh, 10-20 mesh, and 20-40 mesh); and the inorganic material is granular and has a particle size of 1800-2200 mesh (preferably a particle size of 2000 mesh). Where the materials fall in the above ranges, the lost circulation additive can more easily enter loss zones and exhibit good self-adaptability; in addition, the lost circulation additive can achieve plugging while drilling or slug plugging, has simple operation, and undergoes subsequent accumulation and bonding to form a consolidated body, achieving relatively high pressure-bearing strength.

[10] Furthermore, the material of the core layer is obtained by polymerization of polypropylene glycol, toluene diisocyanate, and bis(2-hydroxyethyl)disulfide and curing. The synthesis route is as shown below:

[11] With the use of polypropylene glycol, toluene diisocyanate, and bis(2-hydroxyethyl)disulfide as raw materials for the preparation of the material of the core layer, the tensile strength, elongation at break, and chemical bonding efficiency of the lost circulation additive can be further improved.

[12] Furthermore, the material of the core layer is prepared by a preparation method comprising: at a temperature of 40-70°C, initially mixing the polypropylene glycol with the toluene diisocyanate for a reaction for 10-40 min and then adding the bis(2-hydroxyethyl)disulfide to the system for a reaction for 10-40 min.

[13] Furthermore, the curing is carried out at a temperature of 70-100°C for a period of 5-16 h.

[14] In a preferred embodiment, the material of the core layer is prepared by a preparation method comprising: at a temperature of 40-50°C, initially mixing the polypropylene glycol with the toluene diisocyanate under stirring for 10-20 min, then adding bis(2-hydroxyethyl)disulfide to the system for a polymerization reaction for 15-25 min, and curing the polymerization reaction product at a temperature of 80-90°C for 6-12 h to obtain the material of the core layer. The lost circulation additive thus obtained has more excellent high-temperature resistance, salt resistance, and mechanical strength properties.

[15] In order to improve the above-mentioned problems, according to another aspect of the present disclosure, a composite lost circulation additive is provided, which comprises a lost circulation additive A having a particle size of 10-20 mesh, a lost circulation additive B having a particle size of 20-40 mesh, and optionally a lost circulation additive C having a particle size of 8-10 mesh, wherein the lost circulation additive A, the lost circulation additive B, and the lost circulation additive C are each independently selected from the aforementioned lost circulation additive; and the weight ratio of the lost circulation additive A to the lost circulation additive B to the lost circulation additive C is 1-2 : 1 : 1-2.

[16] It should be noted here that the 10-20 mesh lost circulation additive A means that these particles can pass through a 10-mesh screen but cannot pass through a 20-mesh screen; the 20-40 mesh lost circulation additive B means that these particles can pass through a 20-mesh screen but cannot pass through a 40-mesh screen; the 8-10 mesh lost circulation additive C means that these particles can pass through an 8-mesh screen but cannot pass through a 10-mesh screen.

[17] Based on various reasons above, the lost circulation additive of the present application demonstrates a higher one-time plugging success rate, better pressure-bearing capacity, better compatibility with a drilling fluid, stronger temperature resistance, and strong contamination resistance and salt resistance. The composite lost circulation additive thus compounded has a “bridging-filling-bonding-plugging” effect in fractures and exhibits better plugging and loss prevention effects.

[18] Furthermore, the weight ratio of the lost circulation additive A to the lost circulation additive B to the lost circulation additive C is 1.5-2 : 1 : 1-1.5.

[19] In order to improve the above-mentioned problems, according to another aspect of the present disclosure, a drilling fluid is provided, which comprises the aforementioned lost circulation additive or the aforementioned composite lost circulation additive.

[20] Based on various reasons above, the drilling fluid of the present disclosure achieves loss prevention while drilling or plugging after drilling suspension and can effectively address the technical challenges of fracture-type or porosity-type lost circulation.

[21] In order to improve the above-mentioned problems, according to another aspect of the present disclosure, use of the aforementioned lost circulation additive or the aforementioned composite lost circulation additive in drilling engineering is provided. Based on all the reasons given above, the lost circulation additive and the composite lost circulation additive of the present disclosure can be widely used in the field of drilling fluids for loss prevention and plugging, achieve loss prevention while drilling or plugging after drilling suspension, and address the technical challenges of fracture-type or porosity-type lost circulation. The lost circulation additive and the composite lost circulation additive can also be widely used to solve the problem of well wall instability in fractured formations and to perform wall fixation operation by chemical bonding. DETAILED DESCRIPTION OF EMBODIMENTS

[22] In order to understand the technical features, objects and beneficial effects of the present disclosure more clearly, the technical solutions of the present disclosure are described in detail as below, but cannot be construed as limitations on the implementable scope of the present disclosure.Raw material sources:Polypropylene glycolCAS No.: 25322-69-4Toluene diisocyanateCAS No.: 26471-62-5Bis(2-hydroxyethyl)disulfideCAS No.: 1892-29-1Calcium carbonate (2000 mesh, 800 mesh)Zhengzhou Dongfang Additive Co., Ltd.Bentonite slurryZhengzhou Dongfang Additive Co., Ltd.Xanthan gumZhengzhou Dongfang Additive Co., Ltd.Low-viscosity sodium carboxymethyl celluloseZhengzhou Dongfang Additive Co., Ltd.Walnut shell (10-20 mesh, 20-40 mesh)Zhengzhou Dongfang Additive Co., Ltd. Example 1

[23] 50 g of polypropylene glycol was added to a beaker and heated to 45°C, and stirring was started. 5 g of toluene diisocyanate was then added and stirred for 15 min. 3 g of bis(2-hydroxyethyl)disulfide was then added. Stirring was continued for 20 min to obtain a product system. The above product system was then placed in an oven at 80°C, heated for 6 h, removed, and cooled down to room temperature to obtain the target product (with a number-average molecular weight of 32,000).

[24] The target product was sheared and screened into particles having different particle sizes between 8 and 10 mesh, between 10 and 20 mesh, and between 20 and 40 mesh. These particles were separately uniformly stirred in 2000-mesh superfine calcium carbonate and then further screened to obtain a lost circulation additive C1 having a particle size between 8 and 10 mesh, a lost circulation additive A1 having a particle size between 10 and 20 mesh, and a lost circulation additive B1 having a particle size between 20 and 40 mesh. In the lost circulation additive A1, the weight ratio of the inorganic material to the core layer was 2.2 : 1; in the lost circulation additive B1, the weight ratio of the inorganic material to the core layer was 2.2 : 1; and in the lost circulation additive C1, the weight ratio of the inorganic material to the core layer was 2.2 : 1.Performance evaluation:(I) Evaluation of compatibility with drilling fluid

[25] The lost circulation additives having different mesh sizes from Example 1 were each added to a drilling fluid base slurry. After rolling aging at 150°C for 16 h, the rheological properties and filtration loss performance of the drilling fluids were tested. The formula of the drilling fluid base slurry was: 4 wt% of bentonite slurry + 0.2 wt% of xanthan gum + 0.2 wt% of low-viscosity sodium carboxymethyl cellulose + 95.6 wt% of water. The formula of the drilling fluid system and the evaluation results are shown in Table 1.Table 1Drilling fluid systemStateApparent viscosity AV / mPa·sPlastic viscosity PV / mPa·sDynamic shear force YP / PaFiltration loss FLAPI / mLDrilling fluid base slurryBefore aging3020104.2After aging2814144.8Drilling fluid base slurry + 2 wt% of lost circulation additive C1 (8-10 mesh) + 1 wt% of lost circulation additive A1 (10-20 mesh) + 2 wt% of lost circulation additive B1 (20-40 mesh)Before aging302194.4After aging2915144.6

[26] Note: The weight content of the lost circulation additive in Table 1 refers to the weight percentage of the material relative to the drilling fluid base slurry. For example, “2 wt% of the lost circulation additive C1 (8-10 mesh)” means that the amount of the lost circulation additive C1 (8-10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[27] From compatibility experiments, it can be concluded that the above-mentioned lost circulation additive of the present disclosure does not affect the rheological properties and filtration loss performance of the drilling fluid, exhibits good compatibility, and can be directly added to the drilling fluid for plugging use.(II) Evaluation of bonding strength

[28] The product system in Example 1 was poured into a mold during curing to prepare a cuboid shape having a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The cuboid shape was then cut in the middle with scissors, the cut ends were then spliced together, and the spliced sample was placed in an oven at 80°C and left to stand for 6 h. The spliced sample was placed on a universal tester and tested for tensile strength. The tensile strengths before and after cutting were compared, as shown in Table 2.Table 2StateTensile strength / kPaBefore cutting754.2After cutting750.6

[29] From the experiment of comparing the bonding strengths before and after cutting, it is concluded that after the above-mentioned lost circulation additive of the present disclosure undergoes cutting and then bonding, the tensile strength after bonding is basically the same as that before cutting, and the bonding performance is good; and particles in loss zones will be tightly bonded together to achieve a plugging effect.(III) Plugging pressure-bearing strength test

[30] The lost circulation additives having different mesh sizes obtained in Example 1 were added to drilling fluid base slurries and then tested for plugging pressure-bearing strength using a fracture plugging device (the temperature was set to 120°C, and the plugged fracture was in a compressed state throughout the experiment). The formula of the drilling fluid base slurry was: 4 wt% of bentonite slurry + 0.2 wt% of xanthan gum + 0.2 wt% of low-viscosity sodium carboxymethyl cellulose + 95.6 wt% of water. The formula of the drilling fluid and the evaluation results are shown in Table 3.Table 3Formula of drilling fluidFracture opening / mmPressure-bearing capacity / MPaDrilling fluid base slurry + 1 wt% of lost circulation additive A1 (10-20 mesh) + 2 wt% of lost circulation additive B1 (20-40 mesh) + 2 wt% of superfine calcium carbonate (800 mesh)18.0Drilling fluid base slurry + 1 wt% of walnut shells (10-20 mesh) + 2 wt% of walnut shells (20-40 mesh) + 2 wt% of walnut shells (800 mesh)13.0Drilling fluid base slurry + 2 wt% of lost circulation additive C1 (8-10 mesh) + 1 wt% of lost circulation additive A1 (10-20 mesh) + 2 wt% of lost circulation additive B1 (20-40 mesh) + 3 wt% of superfine calcium carbonate (800 mesh)38.0Drilling fluid base slurry + 2 wt% of walnut shells (8-10 mesh) + 1 wt% of walnut shells (10-20 mesh) + 2 wt% of walnut shells (20-40 mesh) + 3wt% superfine calcium carbonate (800 mesh)32.5

[31] Note: The weight content of the lost circulation additive in Table 3 refers to the weight percentage of the material relative to the drilling fluid base slurry. For example, 2 wt% of the lost circulation additive C1 (8-10 mesh) means that the amount of the lost circulation additive C1 (8-10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[32] It can be seen from the test results that the above-mentioned lost circulation additives of the present disclosure can reach a pressure-bearing strength of 8 MPa at fracture openings of 1 mm and 3 mm; however, the conventional walnut shell lost circulation additives can reach only a pressure-bearing strength of 2.5-3 MPa. The above-mentioned lost circulation additives of the present disclosure have excellent pressure-bearing effects.Example 2

[33] 60 g of polypropylene glycol was added to a beaker and heated to 45°C, and stirring was started. 8 g of toluene diisocyanate was then added and stirred for 15 min. 5 g of bis(2-hydroxyethyl)disulfide was then added. Stirring was continued for 20 min. The above mixture was then placed in an oven at 90°C, heated for 6 h, removed, and cooled down to room temperature to obtain the target product (with a number-average molecular weight of 30000).

[34] The target product was sheared and screened into particles having different particle sizes between 8 and 10 mesh, between 10 and 20 mesh, and between 20 and 40 mesh. These particles were separately uniformly stirred in 2000-mesh superfine calcium carbonate and then further screened to obtain lost circulation additive C2 having a particle size between 8 and 10 mesh, lost circulation additive A2 having a particle size between 10 and 20 mesh, and lost circulation additive B2 having a particle size between 20 and 40 mesh.

[35] In the lost circulation additive A2, the weight ratio of the inorganic material to the core layer was 2.5 : 1; in the lost circulation additive B2, the weight ratio of the inorganic material to the core layer was 2.5 : 1; and in the lost circulation additive C2, the weight ratio of the inorganic material to the core layer was 2.5 : 1.Performance evaluation:(I) Evaluation of compatibility with drilling fluid

[36] The lost circulation additives having different mesh sizes from Example 2 were respectively added to drilling fluid base slurries. After rolling aging at 150°C for 16 h, the rheological properties and filtration loss performance of the drilling fluids were tested. The formula of the drilling fluid base slurry was: 4 wt% of bentonite slurry + 0.2 wt% of xanthan gum + 0.2 wt% of low-viscosity sodium carboxymethyl cellulose + 95.6 wt% of water. The formula of the drilling fluid system and the evaluation results are shown in Table 4.Table 4Drilling fluid systemStateApparent viscosity AV / mPa·sPlastic viscosity PV / mPa·sDynamic shear force YP / PaFiltration loss FLAPI / mLDrilling fluid base slurryBefore aging3020104.2After aging2814144.8Drilling fluid base slurry + 2 wt% of lost circulation additive C2 (8-10 mesh) + 1 wt% of lost circulation additive A2 (10-20 mesh) + 2 wt% of lost circulation additive B2 (20-40 mesh)Before aging292094.2After aging2914154.4

[37] Note: The weight content of the lost circulation additive in Table 4 refers to the weight percentage of the material relative to the drilling fluid base slurry. For example, 2 wt% of the lost circulation additive C2 (8-10 mesh) means that the amount of the lost circulation additive C2 (8-10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[38] From compatibility experiments, it is concluded that the lost circulation additives do not affect the rheological properties or filtration loss performance of the drilling fluid, exhibit good compatibility, and can be directly added to the drilling fluid for plugging use.(II) Evaluation of bonding strength

[39] The product system in Example 2 was poured into a mold during curing to prepare a cuboid shape having a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The cuboid shape was then cut in the middle with scissors, the cut ends were then spliced together, and the spliced sample was placed in an oven at 90°C, and left to stand for 6 h. The spliced sample was placed on a universal tester and tested for tensile strength. The tensile strengths before and after cutting were compared, as shown in Table 5.Table 5StateTensile strength / kPaBefore cutting810.0After cutting806.8

[40] From the experiment of comparing the bonding strengths before and after cutting, it is concluded that after the lost circulation additive undergoes cutting and then bonding, the tensile strength after bonding is basically the same as that before cutting, and the bonding performance is good; and particles in loss zones will be tightly bonded together to achieve a plugging effect.(III) Plugging pressure-bearing strength test

[41] The lost circulation additives having different mesh sizes obtained in Example 2 were added to drilling fluid base slurries and then tested for plugging pressure-bearing strength using a fracture plugging device (the temperature was set to 120°C, and the plugged fracture was in a compressed state throughout the experiment). The formula of the drilling fluid base slurry was: 4 wt% of bentonite slurry + 0.2 wt% of xanthan gum + 0.2 wt% of low-viscosity sodium carboxymethyl cellulose + 95.6 wt% of water. The formula of the drilling fluid and the evaluation results are shown in Table 6.Table 6Formula of pluggingFracture opening / mmPressure-bearing capacity / MPaDrilling fluid base slurry + 1 wt% of lost circulation additive A2 (10-20 mesh) + 2 wt% of lost circulation additive B2 (20-40 mesh) + 2 wt% of superfine calcium carbonate (800 mesh)18.0Drilling fluid base slurry + 1 wt% of walnut shells (10-20 mesh) + 2 wt% of walnut shells (20-40 mesh) + 2 wt% of walnut shells (800 mesh)13.0Drilling fluid base slurry + 2 wt% of lost circulation additive C2 (8-10 mesh) + 1 wt% of lost circulation additive A2 (10-20 mesh) + 2 wt% of lost circulation additive B2 (20-40 mesh) + 3 wt% of superfine calcium carbonate (800 mesh)38.0Drilling fluid base slurry + 2 wt% of walnut shells (8-10 mesh) + 1 wt% of walnut shells (10-20 mesh) + 2 wt% of walnut shells (20-40 mesh) + 3wt% superfine calcium carbonate (800 mesh)32.5

[42] Note: The weight content of the lost circulation additive in Table 6 refers to the weight percentage of the material relative to the drilling fluid base slurry. For example, 2 wt% of the lost circulation additive C2 (8-10 mesh) means that the amount of the lost circulation additive C2 (8-10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[43] It can be seen from the test results that the above-mentioned lost circulation additives of the present disclosure can reach a pressure-bearing strength of 8 MPa at fracture openings of 1 mm and 3 mm; however, the conventional walnut shell lost circulation additives reach only a pressure of 2.5-3 MPa. The lost circulation additives have excellent pressure-bearing effects.Example 3

[44] 62 g of polypropylene glycol was added to a beaker and heated to 45°C, and stirring was started. 8.2 g of toluene diisocyanate was then added and stirred for 15 min. 5.2 g of bis(2-hydroxyethyl)disulfide was then added. Stirring was continued for 20 min. The above mixture was then placed in an oven at 90°C, heated for 6 h, removed, and cooled down to room temperature to obtain the target product (with a number-average molecular weight of 33000).

[45] The target product was sheared and screened into particles having different particle sizes between 8 and 10 mesh, between 10 and 20 mesh, and between 20 and 40 mesh. These particles were separately uniformly stirred in 2000-mesh superfine calcium carbonate and then further screened to obtain lost circulation additive C3 having a particle size between 8 and 10 mesh, lost circulation additive A3 having a particle size between 10 and 20 mesh, and lost circulation additive B3 having a particle size between 20 and 40 mesh.

[46] In the lost circulation additive A3, the weight ratio of the inorganic material to the core layer was 2.5 : 1; in the lost circulation additive B3, the weight ratio of the inorganic material to the core layer was 2.5 : 1; and in the lost circulation additive C3, the weight ratio of the inorganic material to the core layer was 2.5 : 1.Performance evaluation:(I) Evaluation of compatibility with drilling fluid

[47] The lost circulation additives having different mesh sizes from Example 3 were respectively added to drilling fluid base slurries. After rolling aging at 150°C for 16 h, the rheological properties and filtration loss performance of the drilling fluids were tested. The formula of the drilling fluid base slurry was: 4 wt% of bentonite slurry + 0.2 wt% of xanthan gum + 0.2 wt% of low-viscosity sodium carboxymethyl cellulose + 95.6 wt% of water. The formula of the drilling fluid system and the evaluation results are shown in Table 7.Table 7Drilling fluid systemStateApparent viscosity AV / mPa·sPlastic viscosity PV / mPa·sDynamic shear force YP / PaFiltration loss FLAPI / mLDrilling fluid base slurryBefore aging3020104.2After aging2814144.8drilling fluid base slurry + 2 wt% of lost circulation additive C3 (8-10 mesh) + 1 wt% of lost circulation additive A3 (10-20 mesh) + 2 wt% of lost circulation additive B3 (20-40 mesh)Before aging3020104.0After aging2915144.2

[48] Note: The weight content of the lost circulation additive in Table 7 refers to the weight percentage of the material relative to the drilling fluid base slurry. For example, 2 wt% of the lost circulation additive C3 (8-10 mesh) means that the amount of the lost circulation additive C3 (8-10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[49] From compatibility experiments, it is concluded that the lost circulation additives do not affect the rheological properties or filtration loss performance of the drilling fluid, exhibit good compatibility, and can be directly added to the drilling fluid for plugging use.(II) Evaluation of bonding strength

[50] The product system in Example 3 was poured into a mold during curing to prepare a cuboid shape having a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The cuboid shape was then cut in the middle with scissors, the cut ends were then spliced together, and the spliced sample was placed in an oven at 90°C, and left to stand for 6 h. The spliced sample was placed on a universal tester and tested for tensile strength. The tensile strengths before and after cutting were compared, as shown in Table 8.Table 8StateTensile strength / kPaBefore cutting805.0After cutting801.2

[51] From the experiment of comparing the bonding strengths before and after cutting, it is concluded that after the lost circulation additive undergoes cutting and then bonding, the tensile strength after bonding is basically the same as that before cutting, and the bonding performance is good; and particles in loss zones will be tightly bonded together to achieve a plugging effect.(III) Plugging pressure-bearing strength test

[52] The lost circulation additives having different mesh sizes obtained in Example 2 were added to drilling fluid base slurries and then tested for plugging pressure-bearing strength using a fracture plugging device (the temperature was set to 120°C, and the plugged fracture was in a compressed state throughout the experiment). The formula of the drilling fluid base slurry was: 4 wt% of bentonite slurry + 0.2 wt% of xanthan gum + 0.2 wt% of low-viscosity sodium carboxymethyl cellulose + 95.6 wt% of water. The formula of the drilling fluid and the evaluation results are shown in Table 9.Table 9Formula of pluggingFracture opening / mmPressure-bearing capacity / MPaDrilling fluid base slurry + 1 wt% of lost circulation additive A3 (10-20 mesh) + 2 wt% of lost circulation additive B3 (20-40 mesh) + 2 wt% of superfine calcium carbonate (800 mesh)18.0Drilling fluid base slurry + 1 wt% of walnut shells (10-20 mesh) + 2 wt% of walnut shells (20-40 mesh) + 2 wt% of walnut shells (800 mesh)13.0Drilling fluid base slurry + 2 wt% of lost circulation additive C3 (8-10 mesh) + 1 wt% of lost circulation additive A3 (10-20 mesh) + 2 wt% of lost circulation additive B3 (20-40 mesh) + 3 wt% of superfine calcium carbonate (800 mesh)38.0Drilling fluid base slurry + 2 wt% of walnut shells (8-10 mesh) + 1 wt% of walnut shells (10-20 mesh) + 2 wt% of walnut shells (20-40 mesh) + 3wt% superfine calcium carbonate (800 mesh)32.5

[53] Note: The weight content of the lost circulation additive in Table 8 refers to the weight percentage of the material relative to the drilling fluid base slurry. For example, 2 wt% of the lost circulation additive C3 (8-10 mesh) means that the amount of the lost circulation additive C3 (8-10 mesh) is 2 wt% of the weight of the drilling fluid base slurry.

[54] It can be seen from the test results that the above-mentioned lost circulation additives of the present disclosure can reach a pressure-bearing strength of 8 MPa at fracture openings of 1 mm and 3 mm; however, the conventional walnut shell lost circulation additives reach only a pressure of 2.5-3 MPa. The lost circulation additives have excellent pressure-bearing effects.Comparative Example 1

[55] 50 g of polypropylene glycol was added to a beaker and heated to 45°C, and stirring was started. 5 g of toluene diisocyanate was then added and stirred for 15 min. 3 g of adipic dihydrazide was then added. Stirring was continued for 20 min to obtain a product system. The above product system was then placed in an oven at 80°C, heated for 6 h, removed, and cooled down to room temperature to obtain the target product. The target product was sheared and screened into particles having different particle sizes between 8 and 10 mesh, between 10 and 20 mesh, and between 20 and 40 mesh. These particles were separately uniformly stirred in 2000-mesh superfine calcium carbonate and then further screened to obtain lost circulation additive D having a particle size between 8 and 10 mesh, lost circulation additive E having a particle size between 10 and 20 mesh, and lost circulation additive F having a particle size between 20 and 40 mesh.

[56] In the lost circulation additive A, the weight ratio of the inorganic material to the core layer was 1 : 1; in the lost circulation additive B, the weight ratio of the inorganic material to the core layer was 1 : 1; and in the lost circulation additive C, the weight ratio of the inorganic material to the core layer was 1 : 1.

[57] The product system in Comparative Example 1 was poured into a mold during curing to prepare a cuboid shape having a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The cuboid shape was then cut in the middle with scissors, the cut ends were then spliced together, and the spliced sample was placed in an oven at 80°C, and left to stand for 6 h. The spliced sample was placed on a universal tester and tested for tensile strength. The tensile strength after cutting and splicing was only 25.2 kPa, whereas the tensile strength of the lost circulation additive in Example 1 of the present application reached 750.6 kPa.

[58] The lost circulation additive in Comparative Example 1 was added to a drilling fluid base slurry and then tested for plugging pressure-bearing strength using a fracture plugging device. The formula was: drilling fluid base slurry + 2 wt% of lost circulation additive D (8-10 mesh) + 1 wt% of lost circulation additive E (10-20 mesh) + 2 wt% of lost circulation additive F (20-40 mesh) + 3 wt% of superfine calcium carbonate (800 mesh). The pressure-bearing strength is only 3.5 MPa at a fracture opening of 3 mm, which is significantly different from the pressure-bearing capacity of 8 MPa of the lost circulation additive in Example 1 of the present application. Although the acylhydrazone bond also exhibits a bonding effect, the material cannot achieve bonding at a temperature ≥ 60°C. This is because copolymer molecular chains curl and embed acylhydrazone bonds as the temperature rises, making it difficult for the acylhydrazone bonds at the cut site to undergo dynamic exchange, thereby failing to achieve bonding. Moreover, compared with the aforementioned lost circulation additives of the present application, the lost circulation additive in Comparative Example 1 has no high-temperature resistance and cannot achieve bonding effect in deep well loss zones.Comparative Example 2

[59] 50 g of polypropylene glycol was added to a beaker and heated to 45°C, and stirring was started. 5 g of toluene diisocyanate was then added and stirred for 15 min. 3 g of 2,2’-dithiodibenzoic acid was then added. Stirring was continued for 20 min. The above mixture was then placed in an oven at 80°C, heated for 6 h, removed, and cooled down to room temperature to obtain the target product.

[60] The target product was sheared and screened into particles having different particle sizes between 8 and 10 mesh, between 10 and 20 mesh, and between 20 and 40 mesh. These particles were separately uniformly stirred in 2000-mesh superfine calcium carbonate and then further screened to obtain lost circulation additive M having a particle size between 8 and 10 mesh, lost circulation additive J having a particle size between 10 and 20 mesh, and lost circulation additive K having a particle size between 20 and 40 mesh.

[61] In the lost circulation additive M, the weight ratio of the inorganic material to the core layer was 1 : 1; in the lost circulation additive J, the weight ratio of the inorganic material to the core layer was 1 : 1; and in the lost circulation additive K, the weight ratio of the inorganic material to the core layer was 1 : 1.

[62] The product system in Comparative Example 2 was poured into a mold during curing to prepare a cuboid shape having a length of 10 cm, a width of 1 cm, and a thickness of 5 mm. The cuboid shape was then cut in the middle with scissors, the cut ends were then spliced together, and the spliced sample was placed in an oven at 80°C, and left to stand for 6 h. The spliced sample was placed on a universal tester and tested for tensile strength. The tensile strength after cutting and splicing was only 40.4 kPa, whereas the tensile strength of the lost circulation additive in Example 1 of the present application reached 750.6 kPa.

[63] The lost circulation additive in Comparative Example 2 was added to a drilling fluid base slurry and then tested for plugging pressure-bearing strength using a fracture plugging device. The formula was: drilling fluid base slurry + 2 wt% of lost circulation additive M (8-10 mesh) + 1 wt% of lost circulation additive K (10-20 mesh) + 2 wt% of lost circulation additive J (20-40 mesh) + 3 wt% of superfine calcium carbonate (800 mesh). The pressure-bearing strength is only 2.5 MPa at a fracture opening of 3 mm, which is significantly different from the pressure-bearing capacity of 8 MPa of the lost circulation additive in Example 1 of the present application. The degree of bonding between aromatic and polyurethane is relatively low. 

Claims

1. A chemical bonding lost circulation additive, comprising a core layer and an inorganic material coating the outer surface of the core layer, wherein the material of the core layer has a structure as shown in formula I:formula Iwherein in formula I, represents , and the values of m and n are such that the number-average molecular weight of the material of the core layer is 20,000 to 35,000.

2. The chemical bonding lost circulation additive according to claim 1, wherein the material of the core layer is obtained by polymerization of polypropylene glycol, toluene diisocyanate, and bis(2-hydroxyethyl)disulfide and curing.

3. The chemical bonding lost circulation additive according to claim 2, wherein the polymerization comprises: at a temperature of 40-70°C, mixing the polypropylene glycol with the toluene diisocyanate to carry out a reaction for 10-40 min, and then adding the bis(2-hydroxyethyl)disulfide to the system to carry out a reaction for 10-40 min.

4. The chemical bonding lost circulation additive according to claim 2, wherein the polymerization comprises: at a temperature of 40-50°C, mixing the polypropylene glycol with the toluene diisocyanate to carry out a reaction for 10-20 min, and then adding the bis(2-hydroxyethyl)disulfide to the system to carry out a reaction for 15-25 min.

5. The chemical bonding lost circulation additive according to claim 2, wherein the curing is carried out at a temperature of 70-100°C for a period of 5-16 h.

6. The chemical bonding lost circulation additive according to claim 2, wherein the curing is carried out at a temperature of 80-90°C for a period of 6-12 h.

7. The chemical bonding lost circulation additive according to claim 1, wherein the inorganic material is one or more selected from the group consisting of calcium carbonate, magnesium carbonate, bentonite, and talc powder.

8. The chemical bonding lost circulation additive according to claim 1, wherein the weight ratio of the inorganic material to the core layer is 2-4 : 1.

9. The chemical bonding lost circulation additive according to claim 1, wherein the weight ratio of the inorganic material to the core layer is 2-3: 1.

10. The chemical bonding lost circulation additive according to claim 1, wherein the material of the core layer is granular and has a particle size of 8-40 mesh.

11. The chemical bonding lost circulation additive according to claim 1, wherein the inorganic material is granular and has a particle size of 1,800-2,200 mesh.

12. A composite lost circulation additive, comprising a lost circulation additive A having a particle size between 10 and 20 mesh, a lost circulation additive B having a particle size between 20 and 40 mesh, and optionally a lost circulation additive C having a particle size between 8 and 10 mesh, whereinthe lost circulation additive A, the lost circulation additive B, and the lost circulation additive C are each independently a chemical bonding lost circulation additive according to any one of claims 1 to 11; andthe weight ratio of the lost circulation additive A, the lost circulation additive B, and the lost circulation additive C is (1-2) : 1 : (1-2).

13. The composite lost circulation additive according to claim 12, wherein the weight ratio of the lost circulation additive A, the lost circulation additive B, and the lost circulation additive C is (1.5-2) : 1: (1-1.5).

14. A drilling fluid, comprising the chemical bonding lost circulation additive according to any one of claims 1 to 11 or the composite lost circulation additive according to claim 12 or 13.

15. Use of the chemical bonding lost circulation additive according to any one of claims 1 to 11, the composite lost circulation additive according to claim 12 or 13, or the drilling fluid according to claim 14 in drilling engineering. 

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