A leak-proof plugging agent and its preparation method and application

Abstract

The present invention discloses a leak-proof plugging agent and a preparation method and application thereof. The leak-proof plugging agent comprises the following components in percentage by mass: 5-13% polymorphic alloy, 3% MDF, 0%-3% PF-EZCARB, 0.5%-1% brucite fiber, and the remainder is well slurry. The leak-proof plugging agent may also include 3% SQD-98. The present invention optimizes an acid-soluble plugging formula with a plugging pressure bearing capacity of more than 10MPa and an acid solubility rate of more than 70% for crack widths of different openings, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas plugging materials, and in particular to a high-pressure leak-proof plugging agent applicable to fracture reservoirs and capable of unblocking the plugging, as well as a preparation method and application thereof. Background Art

[0002] Well leakage refers to the phenomenon that various working fluids leak into the formation through leakage channels during the drilling process. Once well leakage occurs, the resulting increase in drilling cycle, loss of drilling fluid, and consumption of plugging materials will lead to a large waste of manpower and material resources. About 20-25% of oil and gas wells in the world suffer from well leakage every year, and the economic losses caused by the problem of leaking wells are as high as 2 billion US dollars; for oil and gas production layer leakage, if the drilling fluid leaks into the formation, it may cause permanent damage to the production layer, reduce the oil and gas production in the later period, and more seriously may cause the oil and gas well to be scrapped. With the continuous deepening of oil and gas resource exploration and development in the world, the number of marginal wells, deep wells, and special formation wells is increasing, and with the increasing impact of injection and acid fracturing of oil and gas layers, the pressure bearing capacity of some formations has been greatly reduced; in addition, in order to reduce the cost of exploration and development, many oilfield companies directly carry out long open hole well construction in multi-pressure layers. The above situation makes the problem of well leakage more prominent. In addition, to ensure the safety, speed and efficiency of the drilling process, the bottom hole pressure must be kept higher than the formation pressure during drilling. This pressure difference will cause the loss of drilling fluid when drilling into permeable or fractured formations.

[0003] Well leakage is mainly divided into porous leakage, fracture leakage and cave leakage according to the leakage channel. Among them, fracture leakage has the highest number of leakages and the most far-reaching impact. If natural fractures or artificially induced fractures are encountered during drilling, leakage may occur if they are not properly controlled, and they are often of the lost return type. The existence of formation fractures is difficult to predict, so fracture leakage is hard to prevent. Moreover, after the leakage occurs, since there is no relevant detection instrument to accurately analyze the location, opening and depth of the fractures, the on-site plugging operation is still based on the location of the leakage, the rate of leakage and other related data, and the fractures are judged and processed based on experience. This leads to the on-site well leakage being hard to prevent, and multiple plugging operations are difficult to succeed. Even if the plugging is successful, there will still be repeated leakage in the later period. As for the leakage mechanism and plugging mechanism of fracture leakage, various oilfield companies and scientific research institutions have not yet fully mastered it, which makes the on-site plugging even more blind.

[0004] At present, the most widely used plugging method is bridging plugging, and the reasonable selection of plugging materials is particularly important. Bridging plugging materials, also known as inert plugging materials, are some chemically inert materials added to drilling fluids for drilling plugging. Bridging plugging agents are cheap and widely available. They are mostly inert materials. In addition to their own characteristics, they do not react with other components in the drilling fluid. Within the particle size range below the millimeter level, they have little effect on the performance of the drilling fluid. In foreign countries, bridging plugging materials have been used earlier and are widely used. In the United States, 90% of drilling loss problems are treated with bridging plugging materials. In my country, as early as the 1960s, bridging plugging materials such as rice husks, vermiculite, and walnut shells were used to plug drillings with serious leakage, and certain effects were achieved. With the progress of resource exploration and development, researchers have also studied the bridging plugging process technology. At the same time, many products with reasonable grading and different specifications have been developed and gradually promoted and applied. After entering the new century, with the improvement of the country's chemical industry level, chemical plugging agents and other types of plugging materials have developed rapidly, but the use of bridging plugging materials to deal with drilling leakage problems is still the main means.

[0005] Bridging plugging materials can be divided into three categories according to their shapes: granular plugging materials, fibrous plugging materials and filling powder. Common plugging materials are shown in Table 1.

[0006] Table 1 Common plugging materials

[0007]

[0008] Bridging materials include single inert bridging plugging materials and multiple inert plugging materials, as well as composite bridging plugging materials compounded according to different particle sizes and proportions. Since single plugging materials are limited by particle size and various functions, composite bridging plugging materials have become the protagonist of field applications. Bridging plugging materials are easy to use, safe and reliable, with a wide range of applications and a high success rate. They are the main leak-proof plugging materials on site.

[0009] Bridging plugging mainly uses large particles to build bridges at narrow fractures, and uses particles of various levels for filling, and forms a dense plugging layer through continuous leakage to filtration. In the bridging plugging formula, Wang Shuqi (Wang Shuqi, Tang Jiping, Zhang Bin, etc. High-density drilling fluid plugging technology in the Tarim piedmont tectonic zone [J]. Drilling Fluid and Completion Fluid, 2006 (01): 76-77 + 91.) proposed that the content of bridging large particle plugging material should be maintained at about 10% to 20%, the content of fibrous plugging material should be maintained at 5% to 15%, and the total content of plugging material should be maintained at 20% to 35%. Xue Yuzhi (Xue Yuzhi, Liu Zhendong, Tang Daixu, et al. Study on the formula and regularity of plugging in fractured formations [J]. Drilling Fluids and Completion Fluids, 2009, 26(06): 28-30+93-94.) pointed out that for effective bridging of fractured formations, the plugging formula should be matched with flaky, granular and flocculent filling materials and fibrous materials in addition to the skeleton material, and the particle size should be reasonably matched to achieve rapid plugging and make the plugging device have a higher pressure bearing capacity. Wei Hongchao (Wei Hongchao, Tang Zhijin, Zhang Ling. Plug agent for fractured reservoirs Formula optimization experiment [J]. Drilling Fluids and Completion Fluids, 2010, 27(03): 38-40+97.) conducted a comparative analysis of different bridging materials and proved that the selection of different types of bridging plugging materials is of great significance for successful plugging; Li Jiaxue (Li Jiaxue, Huang Jinjun, Luo Pingya, etc. Mechanism and estimation model of rigid particle plugging while drilling in fractured formations [J]. Acta Petrolei Sinica, 2011, 32(03): 509-513.) established a particle size and concentration estimation model for rigid particles used for plugging while drilling.

[0010] Through the above analysis, the problems and defects of the prior art are as follows:

[0011] (1) The existing plugging materials have poor acid solubility and pressure bearing performance and low temperature resistance.

[0012] (2) The aging quality retention rate of existing plugging materials is low. Summary of the invention

[0013] In order to solve the above technical problems, the present invention provides a leak-proofing and plugging agent and a preparation method and application thereof.

[0014] In a first aspect, the present invention provides a first leak-proofing and plugging agent, which is achieved by adopting the following technical solution.

[0015] A leak-proof plugging agent comprises the following components in percentage by mass: 5-13% of multi-morphology alloy, 3% of MDF, 0%-3% of PF-EZCARB, 0.5%-1% of brucite fiber, and the balance is well slurry.

[0016] Specifically, for a wedge-shaped long crack with an opening of 1×0.5 mm, the leak-proof plugging agent includes the following components in percentage by mass: 5% alloy of 18-30 mesh, 3% MDF, 3% PF-EZCARB, 0.5% brucite fiber, and the rest is well slurry.

[0017] Specifically, for a wedge-shaped long crack with an opening of 2×1 mm, the leak-proof plugging agent includes the following components in percentage by mass: 3% alloy with a mesh size of 12-18, 3% alloy with a mesh size of 18-30, 3% MDF, 3% PF-EZCARB, 0.6% brucite fiber, and the rest is well slurry.

[0018] In a second aspect, the present invention provides a second leak-proofing and plugging agent, which is achieved by adopting the following technical solution.

[0019] A leak-proof plugging agent comprises the following components in percentage by mass: 5-13% of multi-morphology alloy, 3% of MDF, 0%-3% of PF-EZCARB, 0.5%-1% of brucite fiber, 3% of SQD-98, and the balance is well slurry.

[0020] Specifically, for a 3×2mm wedge-shaped long crack, the leak-proof plugging agent includes the following components in percentage by mass: 4% alloy of 10-12 mesh, 4% alloy of 12-18 mesh, 3% alloy of 18-30 mesh, 3% MDF, 3% PF-EZCARB, 3% SQD-98, 0.8% brucite fiber, and the rest is well slurry.

[0021] Specifically, for a 4×3mm wedge-shaped long crack, the leak-proof plugging agent includes the following components in percentage by mass: 5% alloy of 8-12 mesh, 4% alloy of 12-18 mesh, 4% alloy of 18-30 mesh, 3% MDF, 3% PF-EZCARB, 3% SQD-98, 1% brucite fiber, and the rest is well slurry.

[0022] In a third aspect, the present invention provides a method for preparing a leak-proof and plugging agent, which is achieved by adopting the following technical scheme.

[0023] A method for preparing the leak-proof and plugging agent comprises the following steps:

[0024] S101: Well slurry configuration;

[0025] S102: adding a medium-fine alloy particle size of 1 / 4-1 / 3 of the average crack width to the mixed solution prepared in step S101, and adding 0.5%-1% of brucite fiber, and after being evenly dispersed, adding a medium-coarse alloy particle size of 1 / 3-1 / 2 of the average crack width;

[0026] S103: Finally, add the remaining ingredients, stir for 2-3 hours, and let stand for 12-15 hours to obtain a leak-proof plugging agent.

[0027] Furthermore, a certain mass of water was taken, 0.15% NaOH was added to simulate the drilling fluid environment, 0.6% SDTV was added as a viscosity enhancer, 1.5% PF-DFC-200 was added as a high temperature filtration agent, and 0.5% Na2SO3 was added, stirred for 2 hours, and allowed to stand for 24-36 hours.

[0028] In a fourth aspect, the present invention provides three uses of the leak-proof and plugging agent, which are achieved by adopting the following technical solutions.

[0029] The invention discloses an application of the leak-proof plugging agent in the preparation of a bridging plugging agent for drilling working fluid, a bridging plugging agent for cementing working fluid or a bridging plugging agent for testing or repairing working fluid in the development of oil and natural gas.

[0030] This application has the following beneficial effects.

[0031] (1) The present invention selects alloys as bridging particles through the evaluation of basic properties such as plugging material morphology analysis, acid solubility, and pressure bearing performance. The GYD alloy particles have sharp edges and corners, which are conducive to retention in the cracks. The acid solubility rate reaches 76.25%, can withstand temperatures of 180°C, and have strong plugging pressure bearing capacity.

[0032] (2) The present invention preferably uses brucite fiber as the fiber material for netting capture, and its acid solubility is 59.5%, and its dispersion performance is good. The mass retention rate after aging for 48 hours at high temperature of 180°C is 81.5%, and the mass retention rate after aging for 48 hours under high temperature of 180°C and strong alkaline conditions is 75.2%;

[0033] (3) According to the present invention, an acid-soluble plugging formula with a plugging pressure bearing capacity of more than 10 MPa and an acid solubility rate of more than 70% is preferably selected for cracks of different opening widths. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a graph showing the mass retention rate of the plugging fiber after the three fibers of the present invention are hot rolled at 180°C for different times;

[0035] Figure 2 This is a graph showing the quality retention rates of the three types of plugging fibers of the present invention in an alkaline system;

[0036] Figure 3 This is a graph showing the variation of the acid solubility and pressure bearing capacity of the 1×0.5mm formula of the present invention with the reaction time;

[0037] Figure 4 This is a graph showing the variation of the acid solubility and pressure bearing capacity of the 2×1mm formula of the present invention with the reaction time;

[0038] Figure 5 This is a graph showing the variation of the acid solubility and pressure bearing capacity of the 3×2mm formula of the present invention with the reaction time;

[0039] Figure 6 This is a graph showing the change in acid solubility and pressure bearing capacity of the 4×3mm formula of the present invention with reaction time. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0041] 1. Optimization of plugging materials

[0042] 1.1 Bridging materials

[0043] Rigid particles play the role of skeleton in the plugging layer structure, and have the characteristics of high hardness and not easy to deform. In actual operations, quartz, walnut shells, or broken rock chips are often used as rigid particles, but their acid solubility is poor and they cannot effectively remove the plugging after plugging. Therefore, walnut shells, GYD alloys, and limestone are used as bridging particles.

[0044] 1.1.1 Morphology analysis

[0045] From the morphology of walnut shells, GYD and limestone, it can be seen that GYD alloy has sharper edges than walnut shells and limestone. Angular materials are more likely to hang on and bridge in cracks. The sharper the edges of the particles and the more irregular the shape, the more conducive it is to the retention of plugging materials in the cracks.

[0046] 1.1.2 Evaluation of temperature resistance

[0047] A certain mass of walnut shells, GYD alloy and limestone were respectively placed in an oven at 180°C for 24 hours of aging experiment. By comparing the colors before and after aging, it can be found that the color of the walnut shells becomes darker and blacker after aging, indicating that the properties of the walnut shells have changed to a certain extent, while the GYD alloy and limestone have almost no change before and after aging, indicating that the GYD alloy and limestone can withstand 180°C.

[0048] 1.1.3 Acid solubility evaluation

[0049] The sample to be tested was dried at 105°C to a constant weight of 2g, dissolved with 100mL of 15% dilute hydrochloric acid, and reacted at a constant temperature of 80°C in a water bath for 2h. After the reaction, it was filtered with a quantitative slow filter paper and washed with distilled water until there was no chloride ion. The filter paper and insoluble matter were dried at 90°C for 2h, cooled in a dryer for 30min, and weighed. The acid solubility was calculated using the formula: S = [m-(m2-m1)] / m×100%. In the formula, S is the acid solubility, %; m1 is the mass of the filter paper; m2 is the mass of the filter paper and insoluble matter; and m is the mass of the sample. The experimental data and results are shown in Table 2.

[0050] Table 2 Acid solubility test of granular materials

[0051]

[0052]

[0053] Among the three bridging materials, limestone is almost completely acid-soluble, walnut shells are almost completely insoluble, and the acid solubility rate of GYD alloy particles reaches 76.25%.

[0054] 1.1.4 Pressure bearing capacity evaluation

[0055] Base slurry: tap water

[0056] +0.15%NaOH+0.15%Na2CO3+0.6%SDTV+1.5%PF-DFC-200+0.5%Na2SO3

[0057] Experimental slurry 1: 400 mL of well slurry + 3% walnut shell (80-120 mesh) + 5% calcium carbonate powder

[0058] Experimental slurry 2: well slurry 400mL + 3% GYD (80-120 mesh) + 5% calcium carbonate powder

[0059] Experimental slurry 3: well slurry 400mL + 3% limestone (80-120 mesh) + 5% calcium carbonate powder

[0060] Using the HTHP plugging experiment, 5% of PF-EZCARB used on site was added to walnut shell, GYD and limestone to plug 400μm micro-cracks. The test results are shown in Table 3.

[0061] Table 3 Evaluation of the pressure bearing performance of bridging particles

[0062]

[0063] According to the experimental results, the pressure bearing capacity of GYD alloy is 5MPa, which is greater than 4.5MPa of walnut shell and 3Mpa of limestone, indicating that GYD alloy has better pressure bearing capacity.

[0064] 1.2 Fiber materials

[0065] Fiber is a common plugging material. After the fiber material is added to the drilling completion fluid, it is evenly dispersed and enters the leakage channel with the drilling completion fluid. When the fiber length is greater than the crack width, it is easy to form a bridge and capture other fibers passing through, thereby entangled with each other to form a grid structure and enhance the overall structural stability of the plugging layer. Different fibers play different roles in the plugging process: hard fibers with high stiffness can achieve bridging, and soft fibers with low stiffness can make the grid structure denser by entanglement. However, due to the weak overall stiffness of the fiber material itself, it is easy to fail when the pressure difference reaches a certain value, and cannot meet the actual engineering needs when the pressure difference is large. See Table 4.

[0066] Table 4 Fiber material survey

[0067] Serial number name Quantity / g form Sampling location 1 Sepiolite Fiber No. 1 380 Powdered Fiber Lingshou County Dianjin Mineral Products Processing Plant 2 Sepiolite Fiber No. 2 290 Powdered Fiber Lingshou County Dianjin Mineral Products Processing Plant 3 Aluminum silicate fiber 100 Flocculent Fiber Lingshou County Dianjin Mineral Products Processing Plant 4 Mineral Fiber 245 Granular Fiber Lingshou County Dianjin Mineral Products Processing Plant 5 Wood fiber 60 Flocculent Fiber Lingshou County Dianjin Mineral Products Processing Plant 6 Brucite fiber 700 Mixed Fibers Lingshou County Dianjin Mineral Products Processing Plant

[0068] 1.2.1 Morphology analysis

[0069] It can be seen from the six fiber materials of different forms, namely, sepiolite fiber No. 1, sepiolite fiber No. 2, aluminum silicate fiber, mineral fiber, wood fiber and brucite fiber, that sepiolite fiber is a natural mineral fiber, aluminum silicate fiber is a mixture of flocculent plugging material and fiber; mineral fiber is a fiber obtained from mineral rocks with a fibrous structure, and its main components are various oxides; wood fiber is an organic flocculent fiber material obtained by chemical treatment and mechanical processing of natural renewable wood; brucite fiber is a rare fibrous magnesia at home and abroad, and has the characteristics of white color, easy splitting, high fluff yield, etc.

[0070] 1.2.2 Acid solubility evaluation

[0071] The acid solubility of the fiber was evaluated experimentally with the acid solubility of the fiber as an indicator. According to the on-site conditions, a hydrochloric acid solution with a mass fraction of 15% was prepared and placed in a beaker. 1.2g (W1) of sepiolite fiber No. 1 and sepiolite fiber No. 2 were taken and immersed in the hydrochloric acid solution respectively, stirred for 10 minutes to make them fully contact with the hydrochloric acid solution, heated in a 90℃ water bath for 2 hours, sieved, washed, and dried, and the mass of the remaining fiber (W2) was measured. The acid solubility S = [(W1-W2) / W1]×100%.

[0072] According to the experimental results, the acid solubility rates of sepiolite fiber No. 1, sepiolite fiber No. 2, and brucite fiber are 60.75%, 67.92%, and 59.5%, respectively. Therefore, sepiolite fiber No. 1, sepiolite fiber No. 2, and brucite fiber are preliminarily selected as plugging materials. See Table 5.

[0073] Table 5 Acid solubility test of granular materials

[0074] 1.2.3 Test on the influence of drilling fluid performance Sepiolite fiber No. 1, Sepiolite fiber No. 2 and brucite fiber were added to the on-site drilling fluid respectively. After being fully stirred with a low-speed stirrer, their basic properties were tested. Then, they were placed in an aging tank and aged for 16 hours at a hot rolling temperature of 180°C. The experimental results are shown in Table 6.

[0075] Table 6 Basic performance test of experimental pulp before and after adding fiber materials

[0076]

[0077] After adding the three kinds of fibers, the apparent viscosity, plastic viscosity and dynamic shear force of the experimental pulp increased to a certain extent, and the filtration loss decreased, but the basic performance was not much different from that of the original pulp.

[0078] 1.2.4 Evaluation of temperature resistance

[0079] The temperature resistance of plugging fibers in drilling fluid system was evaluated experimentally by taking the mass retention rate of plugging fibers after hot rolling at a certain temperature as an indicator. Three kinds of plugging fibers of a certain mass were added to 400mL of experimental slurry respectively. The experimental slurry formula was 0.6% SDTV + 1.5% PF-DFC-200. After hot rolling at 180℃ for 16h, 32h, and 48h respectively, they were washed and dried, and the mass and breaking strength of the three kinds of plugging fibers after hot rolling were measured. The mass retention rate of plugging fibers was calculated as follows.

[0080]

[0081] Wherein, α is the mass retention rate, %; M1 is the mass of the plugging fiber before hot rolling, g; M2 is the mass of the plugging fiber after hot rolling, g.

[0082] The mass retention rates of the three fibers are as follows Figure 1 The mass retention rate of the plugging fiber after hot rolling at 180℃ for different times is shown in the figure. Analysis shows that after hot rolling at 180℃ for 16h, 32h, and 48h, the mass retention rate of brucite fiber decreases slightly with time, and remains above 80%; the mass retention rate of sepiolite fiber No. 2 decreases with time, and its mass retention rate is lower than 80% after hot rolling at 180℃ for 48h; the mass retention rate of sepiolite fiber No. 1 decreases with time, and its mass retention rate is lower than 80% after hot rolling at 180℃ for 32h.

[0083] 1.2.5 Evaluation of alkali resistance

[0084] The pH value of various commonly used drilling fluid systems is between 8 and 11, that is, to maintain a weak alkaline environment. Therefore, the plugging fiber is required to have good alkali resistance. The mass retention rate and breaking strength retention rate of the plugging fiber after hot rolling at 140°C in a drilling fluid system with a pH value of 12 are used as indicators to experimentally evaluate the alkali resistance of the plugging fiber. Take a certain mass of 5 kinds of plugging fibers and add them to 400mL of experimental slurry. The experimental slurry formula is 0.6% SDTV + 1.5% PF-DFC-200 + 0.2% NaOH (NaOH is added to adjust the pH value of the experimental slurry to 12). After hot rolling at 180°C for 16h, 32h, and 48h, wash and dry, measure the mass and breaking strength of the 5 kinds of plugging fibers after hot rolling, and calculate the mass retention rate according to the following formula.

[0085]

[0086] Where α is the mass retention rate, %; M1 is the mass of the plugging fiber before hot rolling, g; M2 is the mass of the plugging fiber after hot rolling, g. The mass retention rates of the three plugging fibers are given by Figure 2 It can be seen that after being hot-rolled at 180℃ for 16h, 32h, and 48h, the mass retention rate of brucite fiber decreased slightly with time, and remained above 75%; the mass retention rates of the other two plugging fibers after being hot-rolled at 180℃ for 48h were all lower than 70%. The comparative experiment shows that brucite fiber has excellent alkali resistance. (Through the acid melting rate evaluation, it was found that the acid solubility of sepiolite No. 1, No. 2, and brucite fibers was good, so only the experimental results of these three fibers were shown)

[0087] 1.3 Filling powder This application preferably selects three filling powders, namely MDF, SMGF-1 and PF-EZCARB. 1.3.1 Acid solubility (15% dilute hydrochloric acid)

[0088] The test results of the acid solubility of the filling materials are shown in Table 7. The acid solubility of MDF is 80.45%, the acid solubility of SMGF-1 is 64.7%, and the acid solubility of PF-EZCARB is the highest, which is almost completely acid soluble.

[0089] Table 7 Test results of acid solubility of filling materials

[0090] 1.3.2 Evaluation of rheological properties and filtration performance

[0091] The experimental pulps are as follows:

[0092] Base slurry: tap water + 0.15% NaOH + 0.15% Na2CO3 + 0.6% SDTV + 1.5% PF-DFC-200 + 0.5% Na2SO3

[0093] Experimental slurry 1: Well slurry 400mL + 10% PF-EZCARB

[0094] Experimental slurry 2: 400 mL well slurry + 10% SMGF-1

[0095] Experimental slurry 3: 400mL well slurry + 10% MDF

[0096] The basic performance evaluation results are shown in Table 8. Before and after the addition of the plugging material, the apparent viscosity, plastic viscosity, dynamic shear force, and initial and final shear of the base slurry almost increased. Comprehensive comparison shows that the performance of the MDF acid-soluble system is close to that of the simulated well slurry, and the temperature resistance is better.

[0097] Table 8 Changes in rheological filtration properties of the drilling fluid system before and after the addition of plugging materials

[0098]

[0099] Note: The composition of base slurry, experimental slurry 1, experimental slurry 2 and experimental slurry 3 in the table is the same as that in 1.3.3. 1.3.3 Evaluation of plugging performance

[0100] The experimental pulps are as follows:

[0101] Base slurry: tap water + 0.15% NaOH + 0.15% Na2CO3 + 0.6% SDTV + 1.5% PF-DFC-200 + 0.5% Na2SO3

[0102] Experimental slurry 1: Well slurry 400mL + 10% PF-EZCARB

[0103] Experimental slurry 2: 400 mL well slurry + 10% SMGF-1

[0104] Experimental slurry 3: 400mL well slurry + 10% MDF

[0105] Using the HTHP plugging experiment, three groups of experimental slurries, PF-EZCARB, SMGF-1, and MDF, were designed to plug 400 μm microcracks. The test results are shown in Table 9.

[0106] Table 9 Evaluation results of crack plugging performance of 400μm crack width

[0107]

[0108]

[0109] The drilling plugging agents SMGF-1 and PF-EZCARB both have a certain plugging effect on 400μm cracks, and the pressure-bearing plugging agent MDF has a better pressure-bearing effect, reaching 10MPa.

[0110] 2. Optimization and evaluation of leak plugging system

[0111] 2.1 Long crack plugging simulation experiment

[0112] (1) Opening 1×0.5mm long wedge-shaped crack

[0113] Well slurry: tap water + 0.6% SDTV + 1.5% PF-DFC-200 + 0.5% Na2SO3, see Table 10.

[0114] Table 10 Experimental formula for plugging long wedge-shaped cracks with composite plugging materials (1×0.5mm crack)

[0115] serial number Alloy (18-30 mesh) PF-EZCARB MDF Brucite fiber 1-1# 10％ 1-2# 8％ 3％ 1-3# 8％ 3％ 0.5％ 1-4# 5％ 3％ 3％ 0.5％

[0116] Table 11 Experimental results of composite plugging materials for plugging long wedge-shaped cracks (1×0.5 mm cracks)

[0117] serial number Pressure bearing capacity / MPa Leakage volume / mL Crack sealing area / mm 1-1# 5 66 365-385 1-2# 5.5 50 330-350 1-3# 7 34 270-300 1-4# 10 0 100-240

[0118] Analysis shows that when 18-30 mesh alloy particles are used alone, the internal structure of the plugging layer is relatively loose, the pressure bearing capacity is low at only 5MPa, the leakage is large at 66mL, and the crack plugging area is the crack outlet; after adding ultrafine calcium carbonate and brucite fiber, the plugging layer structure is relatively dense, the pressure bearing capacity of the plugging layer increases to 7MPa, the crack leakage is reduced to 34mL, and the crack plugging area moves forward; finally, after adding the pressure plugging agent MDF, the pressure bearing capacity of the plugging layer reaches 10MPa. Therefore, the 1-4# formula is selected as the formula of the wedge-shaped long crack system with an opening of 1×0.5mm, and the specific formula is: well slurry + 5% alloy (18-30 mesh) + 3% MDF + 3% PF-EZCARB + ​​0.5% brucite fiber.

[0119] (2) Opening 2×1mm long wedge-shaped crack

[0120] Well slurry: tap water + 0.6% SDTV + 1.5% PF-DFC-200

[0121] Table 12 Experimental formula for plugging long wedge-shaped cracks with composite plugging materials (2×1 mm cracks)

[0122] Table 13 Experimental results of composite plugging materials for plugging long wedge-shaped cracks (2×1 mm cracks)

[0123] serial number Pressure bearing capacity / MPa Leakage volume / mL Crack sealing area / mm 2-1# 5.5 230 600-750 2-2# 6.5 206 590-748 2-3# 7 195 575-732 2-4# - - - 2-5# 10 114 270-500 / 540-720

[0124] Brucite fiber can capture alloy particles through three-dimensional web tensioning and bending extrusion binding, forming plugging fiber and particle aggregates, increasing the resistance to the migration of bridging plugging particles, making them easier to stay in the cracks, and significantly increasing the density of the plugging layer; at the same time, the plugging fiber can improve the compressive strength and shear strength of the plugging layer, avoiding the plugging layer from extrusion crushing instability and shear slip instability under the action of external load. However, too high a concentration of brucite fiber can easily cause a door to be sealed, such as 2-4#. Finally, after adding the pressure-bearing plugging agent MDF, the pressure bearing capacity of the plugging layer reaches 10MPa. Therefore, the 2-5# formula is selected as the high-temperature resistant fiber plugging system formula for the wedge-shaped long crack with an opening of 2×1mm. The specific formula is: well slurry + 3% alloy (12-18 mesh) + 3% alloy (18-30 mesh) + 3% MDF + 3% PF-EZCARB + ​​0.6% brucite fiber.

[0125] (3) 3×2mm wedge-shaped long crack

[0126] Combined with the experimental formula results of composite plugging materials for plugging 2×1mm wedge-shaped long cracks, the formula optimization experiment of plugging system for 3×2mm wedge-shaped long cracks was carried out through the reasonable compounding of alloy particles, MDF pressure plugging agent, PF-EZCARB and brucite fiber. Table 13 and Table 14 show the experimental formula and results of alloy particles, pressure plugging agent and brucite fiber for plugging 3×2mm wedge-shaped long cracks.

[0127] Well slurry: tap water + 0.6% SDTV + 1.5% PF-DFC-200.

[0128] Table 14 Experimental formula for plugging long wedge-shaped cracks with composite plugging materials (3×2 mm cracks)

[0129] Table 15 Experimental results of composite plugging materials for plugging long wedge-shaped cracks (3×2 mm cracks)

[0130] serial number Pressure bearing capacity / MPa Leakage volume / mL Crack sealing area / mm 3-1# 4 360 540-610 3-2# 5 350 523-602 3-3# 5 345 500-576 3-4# 7.5 280 466-526 3-5# 8 265 425-502 3-6# - - - 3-7# 10 138 348-428 3-8# 11 90 210-370

[0131] Analysis shows that when using alloy particle plugging experimental formulas with different mesh sizes, the pressure bearing capacity of the plugging layer generally does not exceed 5MPa, and the crack leakage is large; with the increase in the concentration of brucite fiber and pressure-bearing plugging agent, the density of the plugging layer is significantly enhanced, the pressure bearing capacity of the plugging layer is significantly increased, the crack leakage is reduced to 90mL, and the crack plugging area moves forward. When 1% brucite plugging fiber is added, its concentration is too high and it overlaps into a net outside the crack opening, forming a "sealed door", and the plugging effect is poor.

[0132] The optimal amount of brucite plugging fiber is 1%, which can be involved with alloy particles and pressure-bearing plugging agent to form a dense pressure-bearing plugging layer. Therefore, the 3-8# formula is selected as the formula of the high-temperature fiber plugging system for wedge-shaped long cracks with an opening of 3×2mm, which can withstand a pressure of 11Mpa. The specific formula is: well slurry + 4% alloy (10-12 mesh) + 4% alloy (12-18 mesh) + 3% alloy (18-30 mesh) + 3% MDF + 3% SQD-98 + 3% PF-EZCARB + ​​0.8% brucite fiber.

[0133] (4) Opening 4×3mm long wedge-shaped crack

[0134] Tables 16 and 17 show the experimental formulas and results of alloy particles, MDF pressure plugging agent, SQD-98 and brucite fiber plugging 4×3mm wedge-shaped long cracks. Analysis shows that when alloy particles of different mesh sizes are used alone, the plugging layer has a loose structure, a low pressure bearing capacity of only 5.5MPa, a large crack leakage, and the crack plugging area is the crack outlet; after adding brucite fiber, the internal structure of the plugging layer is further optimized, the pressure bearing capacity of the plugging layer is improved, the crack leakage is significantly reduced, and the crack plugging area moves forward. When 1.2% brucite fiber is added, its concentration is too high and it overlaps outside the crack opening to form a network, forming a "sealed door". The optimal amount of brucite fiber is 1%. After adding pressure plugging agents MDF and SQD-98, they can fill the pores between alloy particles, the pressure bearing capacity of the plugging layer is increased to 11MPa, the crack leakage is reduced to 104mL, and the crack plugging area moves forward.

[0135] Therefore, the 4-8# formula was selected as the formula of the high-temperature resistant fiber plugging system for wedge-shaped long cracks with an opening of 4×3 mm. The specific formula is: well slurry + 5% alloy (8-12 mesh) + 4% alloy (12-18 mesh) + 4% alloy (18-30 mesh) + 3% MDF + 3% SQD-98 + 3% PF-EZCARB + ​​1% brucite fiber.

[0136] Table 16 Experimental formula for plugging long wedge-shaped cracks with composite plugging materials (4×3 mm cracks)

[0137]

[0138]

[0139] Table 17 Experimental results of composite plugging materials for plugging long wedge-shaped cracks (4×3mm cracks)

[0140] serial number Pressure bearing capacity / MPa Leakage volume / mL Crack sealing area / mm 4-1# 4 380 980-995 4-2# 5.5 334 975-990 4-3# 5.5 330 974-986 4-4# 6.5 270 850-890 4-5# 7 255 840-890 4-6# - - - 4-7# 9 135 790-835 4-8# 11 104 770-900

[0141] 2.2 Acid dissolution plugging experiment

[0142] (1) Opening 1×0.5mm long wedge-shaped crack

[0143] According to the preferred formula "well slurry + 5% alloy (18-30 mesh) + 3% MDF + 3% PF-EZCARB + ​​0.5% brucite fiber", acid dissolution and pressure bearing performance experiments after acid dissolution were carried out. 5g alloy (18-30 mesh), 3g MDF, 3g PF-EZCARB and 0.5g brucite fiber were placed in 6 beakers respectively, and 50mL 15% dilute hydrochloric acid was added. The acid solubility was tested after reacting for 2h, 4h, 6h, 8h, 16h and 24h respectively. The remaining samples were filtered, dried and added to 100mL base slurry to carry out pressure bearing performance test with a seam width of 1mm. Figure 3As shown in Table 18, the acid solubility rate of the formula can reach 71.5% after 8 hours of acid solubility, and it gradually loses its pressure bearing capacity.

[0144] Table 18 Changes of acid solubility rate and pressure bearing capacity of plugging formula over time

[0145] Reaction time / h Acid solubility / % Pressure bearing capacity / MPa 2 31.8％ 7 4 50.9％ 4.5 6 62.6％ 1.5 8 71.5％ 0.5 16 78.5％ 24 81.3％

[0146] (2) Opening 2×1mm long wedge-shaped crack

[0147] According to the preferred formula "well slurry + 3% alloy (12-18 mesh) + 3% alloy (18-30 mesh) + 3% MDF + 3% PF-EZCARB + ​​0.6% brucite fiber", acid dissolution and pressure bearing performance experiments after acid dissolution were carried out. 3g alloy (12-18 mesh), 3g alloy (18-30 mesh), 3g MDF, 3g PF-EZCARB and 0.6g brucite fiber were placed in 6 beakers respectively, and 50mL 15% dilute hydrochloric acid was added. The acid solubility was tested after reacting for 2h, 4h, 6h, 8h, 16h and 24h respectively. The remaining samples were filtered, dried and added to 100mL base slurry to carry out pressure bearing performance test with a seam width of 2mm. Figure 4 As shown in Table 19, the acid dissolution rate of the formula can reach 70.3% after 8 hours of acid dissolution, and it gradually loses its pressure bearing capacity.

[0148] Table 19 Changes of acid dissolution rate and pressure bearing capacity of plugging formula over time

[0149] Reaction time / h Acid solubility / % Pressure bearing capacity / MPa 2 30.6 6 4 49.5 3 6 62.8 1 8 70.3 0.5 16 75.6 0 24 78.6 0

[0150] (3) 3×2mm wedge-shaped long crack

[0151] According to the preferred formula "well slurry + 4% alloy (10-12 mesh) + 4% alloy (12-18 mesh) + 3% alloy (18-30 mesh) + 3% SQD-98 + 3% MDF + 3% PF-EZCARB + ​​0.8% brucite fiber", acid dissolution and pressure bearing performance experiments after acid dissolution were carried out. 4g alloy (10-12 mesh), 4g alloy (12-18 mesh), 3g alloy (18-30 mesh), 3g MDF, 3g PF-EZCARB, 3g SQD-98 and 0.8g brucite fiber were placed in 6 beakers respectively, and 50mL 15% dilute hydrochloric acid was added. The acid solubility was tested after reacting for 2h, 4h, 6h, 8h, 16h and 24h respectively. The remaining sample was filtered, dried and added to 100mL base slurry to carry out pressure bearing performance test with a seam width of 3mm. Figure 5 As shown in Table 20, after 16 hours of acid dissolution, the acid dissolution rate of the formula can reach 69.4%, and the pressure bearing capacity is lost.

[0152] Table 20 Changes of acid solubility rate and pressure bearing capacity of plugging formula over time

[0153] Reaction time / h Acid solubility / % Pressure bearing capacity / MPa 2 28.9 5.5 4 41.2 2.5 6 51.3 3 8 64.6 1 16 69.4 0 24 74.2 0

[0154] (4) Opening 4×3mm long wedge-shaped crack

[0155] According to the preferred formula "well slurry + 5% alloy (8-12 mesh) + 4% alloy (12-18 mesh) + 4% alloy (18-30 mesh) + 3% MDF + 3% SQD-98 + 3% PF-EZCARB + ​​1% brucite fiber", acid dissolution and pressure bearing performance experiments after acid dissolution were carried out. 5g alloy (8-12 mesh), 4g alloy (12-18 mesh), 4g alloy (18-30 mesh), 3g MDF, 3g PF-EZCARB, 3g SQD-98 and 1g brucite fiber were placed in 6 beakers respectively, and 50mL 15% dilute hydrochloric acid was added. The acid solubility was tested after reacting for 2h, 4h, 6h, 8h, 16h and 24h respectively. The remaining samples were filtered, dried and added to 100mL base slurry to carry out pressure bearing performance test with a seam width of 4mm. Figure 6 As shown in Table 21, after 8 hours of acid dissolution, the acid dissolution rate of the formula can reach 61.1%, and the pressure bearing capacity is lost.

[0156] Table 21 Changes of acid dissolution rate and pressure bearing capacity of plugging formula over time

[0157] Reaction time / h Acid solubility / % Pressure bearing capacity / MPa 2 29.8 4 4 42.5 1.5 6 51.1 0.5 8 61.1 0 16 70.3 0 24 76.4 0

[0158] The above experiments show that for millimeter-level cracks, the plugging effect of using a certain type of plugging material alone is poor, and it is impossible to form a dense pressure-bearing plugging layer. It is necessary to reasonably compound different types of plugging materials to give full play to their synergistic effect. Therefore, different types of high-temperature resistant plugging materials were selected. Among them, alloy particles are used as bridging particles to bridge the cracks and form the skeleton structure of the plugging layer; SQD-98 is an elastic deformation material with a large compression recovery rate; MDF and PF-EZCARB fill the pores between the bridging particles to reduce the leakage of the cracks; brucite fibers can form a mesh structure in the plugging layer through three-dimensional mesh reinforcement and bending and extrusion restraint, improve the compressive strength and shear strength of the plugging layer, avoid the extrusion crushing instability and shear slip instability of the plugging layer under external loads, and improve the pressure bearing capacity of the plugging layer.

[0159] The present invention provides a method for preparing a high-pressure leak-proof plugging agent capable of unblocking fracture reservoirs, comprising the following steps:

[0160] S101, slurry preparation: first take a certain mass of tap water, add 0.15% NaOH to simulate the drilling fluid environment, determine the mineralization of water, promote the dispersion of other reagents, add 0.6% SDTV as a viscosity enhancer, 1.5% PF-DFC-200 as a high temperature filtration agent, and continue to add 0.5% Na2SO3 to improve the anti-aging performance of the drilling fluid, use a slurry preparation machine to stir for 2 hours, and let it stand for 24 hours;

[0161] S102, in the plugging material, firstly, GYD alloy with mainly medium-fine particles and a particle size of 1 / 4-1 / 3 of the average width of the crack is added, and 0.5%-1% of brucite fiber is added as an auxiliary. The brucite fiber has the ability of laying nets and capturing, which can improve the suspension of the plugging material and make the plugging material more dispersed. After the plugging material is evenly dispersed, GYD alloy with mainly medium-coarse particles and a particle size of 1 / 3-1 / 2 of the average width of the crack is added;

[0162] S103, finally add 3% MDF or 3% MDF and 3% PF-EZCARB or 3% MDF and SQD-98 to improve the overall pressure bearing capacity of the plugging slurry, use a slurry mixing machine to stir for 2 hours, let it stand for 12 hours, and obtain a high-pressure leak-proof plugging agent that can be used for fracture reservoirs.

[0163] The reservoir space of the buried hill is mainly composed of fractures, and dissolution pores along the fractures can occasionally be seen, resulting in the fragmentation of strata and the development of fracture networks near the buried hill. The top surface of the Archean in this area is a geological interface that has been subjected to long-term weathering and erosion. The granite gneiss that make up these strata are relatively easy to weather and fracture, and there are various fractures during the weathering period.

[0164] The shape and size of cracks are related to the type, physical properties, strength, bonding surface type and shear strength of the rock. The size grading and concentration of the plugging material should be considered comprehensively.

[0165] The bridge plugging efficiency enhancement technology adopts a two-stage process, and the specific ideas are as follows: the first stage of the bridge plugging slurry is mainly composed of medium and fine particles, and GYD alloy with a particle size of 1 / 4-1 / 3 of the average width of the crack and 0.5%-1% brucite fiber are selected. It is pumped using a special plugging device. After entering the deep leaking layer, the plugging material accumulates into a plug. As time goes by, the fiber bonds the bridge plug into a whole to avoid subsequent leakage; the second stage of the bridge plugging slurry increases the amount of medium and coarse particles, and MDF and PF-EZCARB are selected to improve the overall pressure bearing capacity of the plugging slurry. During construction, coarse particles are added from the tank surface after the pump is turned on to achieve graded plugging, and a mud pump is used for pumping.

[0166] Application Examples

[0167] Well BZ19-6-X is a deep exploration well in the BZ19-6 block, and its target layer is the Archean buried hill. During the period, frequent leakage occurred at 4898m, 4952m, 4960m and 4972.5m. It was judged that the upper fault was leaking again or a new micro-fracture formation was encountered. After the plugging slurry was injected and prepared for displacement, the land informed that the plugging slurry concentration was increased to 35%: 10 cubic meters of well slurry + 15% PF-SZDL + 15% SEAL + 5% EZCARB, but all were ineffective. It was decided to use the indoor preferred formula "well slurry + 5% alloy (8-12 mesh) + 4% alloy (12-18 mesh) + 4% alloy (18-30 mesh) + 3% MDF + 3% SQD-98 + 3% PF-EZCARB + ​​1% brucite fiber" to pump 8m of plugging slurry in a small displacement. 3 The displacement is in place, and the displacement volume is increased to 1100L / min. The drilling tool is placed at the bottom of the well before the plugging slurry comes out of the drill bit. During this period, the plugging slurry comes out of the drill bit, the leakage rate decreases, and the liquid level in the circulation pool gradually stabilizes. The liquid level at the wellhead is observed statically, and there is no overflow or leakage.

[0168] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A leak-proof plugging agent, characterized in that: The invention comprises the following components in percentage by mass: 5-13% multi-morphology alloy, 3% MDF, 3% PF-EZCARB, 0.5%-1% brucite fiber, and the balance is well slurry.

2. A leak-proofing and plugging agent according to claim 1, characterized in that: For the wedge-shaped long crack with an opening of 1×0.5mm, the leak-proof plugging agent includes the following components in mass percentage: 5% alloy with a mesh size of 18-30, 3% MDF, 3% PF-EZCARB, 0.5% brucite fiber, and the rest is well slurry.

3. The leak-proof and plugging agent according to claim 1, characterized in that: For the wedge-shaped long cracks with an opening of 2×1mm, the leak-proof plugging agent includes the following components in mass percentage: 3% alloy of 12-18 mesh, 3% alloy of 18-30 mesh, 3% MDF, 3% PF-EZCARB, 0.6% brucite fiber, and the rest is well slurry.

4. A leak-proof plugging agent, characterized in that: The invention comprises the following components in percentage by mass: 5-13% multi-morphology alloy, 3% MDF, 3% PF-EZCARB, 0.5%-1% brucite fiber, 3% SQD-98, and the balance is well slurry.

5. The leak-proofing and plugging agent according to claim 4, characterized in that: For the 3×2mm wedge-shaped long cracks, the leak-proof plugging agent includes the following components in mass percentage: 4% alloy of 10-12 mesh, 4% alloy of 12-18 mesh, 3% alloy of 18-30 mesh, 3% MDF, 3% SQD-98, 3% PF-EZCARB, 0.8% brucite fiber, and the rest is well slurry.

6. The leak-proofing and plugging agent according to claim 4, characterized in that: For the 4×3mm wedge-shaped long cracks, the leak-proof plugging agent includes the following components in mass percentage: 5% alloy of 8-12 mesh, 4% alloy of 12-18 mesh, 4% alloy of 18-30 mesh, 3% MDF, 3% PF-EZCARB, 3% SQD-98, 1% brucite fiber, and the rest is well slurry.

7. A method for preparing the leak-proof and plugging agent according to any one of claims 1 to 6, characterized in that: The following steps are involved: S101: Well slurry configuration; S102: adding a medium-fine alloy particle size of 1 / 4-1 / 3 of the average crack width to the mixed solution prepared in step S101, and adding 0.5%-1% of brucite fiber, and after being evenly dispersed, adding a medium-coarse alloy particle size of 1 / 3-1 / 2 of the average crack width; S103: Finally, add the remaining ingredients, stir for 2-3 hours, and let stand for 12-15 hours to obtain a leak-proof plugging agent.

8. The method for preparing a leak-proof and plugging agent according to claim 7, characterized in that: In step S101, the slurry configuration method is as follows: take a certain mass of water, add 0.15% NaOH to simulate the drilling fluid environment, add 0.6% SDTV as a viscosity enhancer, 1.5% PF-DFC-200 as a high temperature filtration agent, continue to add 0.5% Na2SO3, stir for 2 hours, and let stand for 24-36 hours.

9. Use of the leak-proof plugging agent according to any one of claims 1 to 6 in the preparation of a bridging plugging agent for drilling working fluid, a bridging plugging agent for cementing working fluid, or a bridging plugging agent for testing or repairing working fluid in the development of oil and natural gas.

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