Water-based cementation plugging agent for depleted sandstone reservoir and preparation method of water-based cementation plugging agent

Abstract

The invention discloses a water-based cementing plugging agent for a depleted sandstone reservoir and a preparation method of the water-based cementing plugging agent. The water-based cementation plugging agent for the depleted sandstone reservoir comprises the following components in parts by mass: 60-80 parts of a water-soluble expansion cementation component and 10-20 parts of a slow-release degradation component, the water-soluble expansion cementing component is prepared from surface modified spherical nano silicon dioxide, modified starch, guanidine gum, natural latex powder and polyvinyl alcohol; the slow-release degradation component is prepared from polyvinyl alcohol and thermostable amylase. The water-based cementing plugging agent can effectively improve the pressure-bearing plugging capacity of drilling and completion fluid in a depleted sandstone reservoir, reduce the risk of well leakage during drilling and completion of the depleted reservoir, and reduce the risk of solid-phase plugging caused by flow-back in later production.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas drilling, and particularly relates to a water-based cementing plugging agent for a depleted sandstone reservoir and a preparation method thereof. Background Art

[0002] Currently, most shallow oil and gas fields in China are in the mid-to-late production stage, with formation pressure depletion. During drilling and completion operations, the large pressure differential between the working fluid in the wellbore and the formation makes it very easy for leakage to occur, thereby contaminating the reservoir.

[0003] The following technical measures are mainly used for drilling and completion operations in depleted reservoirs: (1) Use a strong plugging water-based drilling fluid system to enhance plugging; (2) Use a solid-free or low-solid water-based drilling fluid system. The above technical measures mainly have the following problems: (1) The strong plugging water-based drilling fluid system requires the use of a large amount of plugging agents, which will inevitably cause solid-phase plugging damage, and the solid-phase plugging damage of most high-efficiency plugging agent materials is difficult to remove; (2) The plugging pressure bearing capacity of the solid-free or low-solid water-based drilling fluid system is weak, the permeability of the depleted sandstone reservoir is good, the operating pressure difference is large, and the risk of leakage is high; (3) The use of temporary plugging agent materials requires the use of plugging fluid in the later stage, which will also increase the on-site operation process. Therefore, during the drilling and completion operations of depleted sandstone reservoirs, the drilling and completion fluid system faces the problem of providing good plugging pressure bearing capacity while not causing solid-phase plugging damage to the reservoir. From the above, it can be seen that there is currently a lack of water-based cementitious plugging agent materials for drilling and completion fluid systems that are suitable for depleted reservoirs and can both withstand pressure and seal while avoiding damage from solid-phase clogging.

[0004] In summary, in order to solve the drilling safety and reservoir protection problems of leak prevention and plugging of depleted sandstone reservoirs and production backflow reservoir protection, it is urgent to develop a water-based cementing plugging agent for depleted sandstone reservoirs. Summary of the Invention

[0005] The purpose of the present invention is to provide a water-based cementitious plugging agent for depleted sandstone reservoirs. The water-based cementitious plugging agent of the present invention can effectively improve the pressure-bearing and plugging capacity of drilling and completion fluids in depleted sandstone reservoirs, reduce the risk of well leakage during drilling and completion of depleted reservoirs, and reduce the risk of solid phase blockage in later production backflow.

[0006] The water-based cementing plugging agent for depleted sandstone reservoirs provided by the present invention has the following composition by weight: 60-80 parts of water-soluble swelling cementing component and 10-20 parts of slow-release degradation component; The water-soluble swelling cementing component is prepared from surface-modified spherical nano-silica, modified starch, guar gum, natural rubber latex powder and polyvinyl alcohol; The slow-release degradation component is prepared from polyvinyl alcohol and high-temperature amylase.

[0007] Preferably, the surface-modified spherical nano-silica is obtained by surface-modifying spherical nano-silica with aminosilane; The spherical nano-silicon dioxide can be produced by Changzhou Konada New Material Technology Co., Ltd., Shanghai Naio Nano Technology Co., Ltd. and / or Nangong Jingrui Alloy Products Co., Ltd.; The aminosilane is γ-aminopropyltriethoxysilane.

[0008] The specific preparation process is as follows: In a reaction kettle, 100 parts of deionized water were added, and 10 to 20 parts of spherical nano-silica were added while stirring at 100 rpm. After stirring for 1 to 2 hours, 1 to 2 parts of aminosilane were added, and the mixture was stirred at 50 rpm for 2 to 3 hours. After sufficient reaction, the mixture was dried, crushed, and passed through a 2000 mesh sieve to obtain surface-modified spherical nano-silica. Preferably, the feeding rate of the spherical nano-silica is 10 parts per hour; The feeding rate of the aminosilane is 2 parts per hour; The mass ratio of the spherical nano-silica and aminosilane is 10:1; The aminosilane aqueous solution has a mass percentage concentration of 1-2%.

[0009] Preferably, the polyvinyl alcohol is polyvinyl alcohol powder 1788 (PVA), the molecular formula of which is C6H 10 O3.

[0010] Preferably, the modified starch is one of oxidized starch (Dezhou Runde Starch Co., Ltd.), pregelatinized modified starch (Jinan Yibo Chemical Co., Ltd.) and pregelatinized starch (Anhui Weimao Biotechnology Co., Ltd.), or a mixture of the two in any proportion; The guar gum is one of hydroxypropyl guar gum (Hebei Yufei Chemical Co., Ltd.), guar gum (Renqiu Litian Chemical Co., Ltd.) and locust bean gum (Wuhan Henry Biotechnology Co., Ltd.), or a mixture of the two in any proportion.

[0011] Preferably, the natural latex is one of low ammonia natural latex (Shandong Zhonghan Chemical Co., Ltd.), low ammonia natural latex (Shandong Guangju Biotechnology Co., Ltd.) and low ammonia natural latex (Shandong Shengrun Chemical Co., Ltd.), or a mixture of two of them in any proportion, with a total solid content of >60%.

[0012] Preferably, the natural rubber latex powder is obtained by freeze-drying and pulverizing natural rubber latex; The high-temperature amylase is a high-temperature resistant α-amylase, such as the high-temperature resistant α-amylase produced by Shanghai Huashang Xiangyang Biotechnology Co., Ltd., Jiangsu Jiujia Biotechnology Co., Ltd. and / or Guangdong Mingcheng Biotechnology Co., Ltd.

[0013] The composition of the water-based cementitious plugging agent of the present invention is specifically any one of the following: 1) 60 parts of water-soluble swelling cementing component and 10 parts of slow-release degradation component; 2) 60 parts of water-soluble swelling cementing component and 20 parts of slow-release degradation component; 3) 70 parts of water-soluble swelling cementing component and 10 parts of slow-release degradation component; 4) 70 parts of water-soluble swelling cementing component and 20 parts of slow-release degradation component; 5) 80 parts of water-soluble swelling cementing component and 10 parts of slow-release degradation component; 6) 80 parts of water-soluble swelling binder component and 20 parts of slow-release degradation component.

[0014] The present invention further provides a method for preparing the water-based cementitious plugging agent, comprising the following steps: S1. Surface-modified spherical nano-silica, modified starch, and guar gum are mixed, natural rubber latex powder is added, and curing is performed, and finally polyvinyl alcohol is added and stirred to obtain a water-soluble swelling cementitious component; S2, mixing polyvinyl alcohol with high-temperature amylase to obtain a slow-release degradation component; S3, mixing the water-soluble swelling cement component and the slow-release degradation component.

[0015] In the present invention, the natural rubber latex powder is obtained by freeze-drying and pulverizing natural rubber latex; The freeze-drying temperature is -30°C to -10°C.

[0016] Step S1 specifically includes the following steps: The surface-modified spherical nano-silica, the modified starch and the guar gum are added to the reactor in sequence and stirred for 2 to 3 hours. After stirring evenly, the natural rubber latex powder is added and stirred for 2 to 3 hours. The humidity in the reactor is then controlled to be 70% to 80%, and the mixture is cured under stirring for 2 to 3 hours. The polyvinyl alcohol is then added and stirred for 2 to 3 hours. The mixture is vacuum dried and crushed at low temperature and passed through a 100-mesh sieve to obtain the water-soluble swelling binder component.

[0017] Step S2 specifically includes the following steps: Deionized water was added to the reactor, and the polyvinyl alcohol was added under stirring, and the mixture was stirred at room temperature for 2 to 3 hours. The high-temperature amylase was then added, and the mixture was stirred at room temperature for 3 to 4 hours. The mixture was vacuum dried, crushed, and passed through a 100-mesh sieve to obtain the slow-release degradation component.

[0018] Preferably, the addition rate of the modified starch, guar gum, natural latex powder, polyvinyl alcohol and high-temperature amylase is 50 parts per hour; The feeding rate of the water-soluble swelling cementing component and the slow-release degradation component is 100 parts per hour; The reaction temperature, unless otherwise specified, is room temperature; the low-temperature vacuum drying temperature is -20°C to -10°C; the vacuum drying temperature is room temperature.

[0019] The water-based cementitious plugging agent of the present invention is added to the drilling and completion working fluid system and enters the rock pores of the depleted sandstone reservoir. The swelling cementing component in the water-based cementitious plugging agent adheres to the cemented rock under the action of gradual hydration and expansion to achieve the plugging and pressure-bearing function, thereby meeting the plugging and leakage prevention needs of the depleted sandstone reservoir during the drilling and completion operations. The slow-release degradation component in the water-based cementitious plugging agent gradually dissolves in the drilling and completion fluid system to release high-temperature amylase, which then reacts with the natural polymer in the swelling cementing component, gradually degrading the swelling cementing component, and finally achieving the unblocking of the plugging layer, thereby meeting the needs of production testing after the drilling and completion operations, without increasing on-site operations, and realizing the integrated completion, leakage prevention and production operations of the depleted sandstone reservoir.

[0020] The present invention has the following beneficial technical effects: 1. The water-based cementitious plugging agent provided by the present invention comprises a water-soluble swelling cementing component, which provides a rigid support structure through surface-modified spherical silica to enhance the plugging quality and pressure-bearing capacity, reduces filtration and improves the plugging quality through the hydration and expansion of modified starch, enhances the spatial cross-linking properties through the hydration and expansion of guanidine gum, and provides elasticity and adsorption and bonding properties through natural rubber latex powder. The above components and mechanisms provide the functions of plugging pressure and cementing formations, and provide the plugging and leakage prevention function of the drilling and completion fluid system during drilling and completion of depleted sandstone reservoirs.

[0021] 2. The water-based cementitious plugging agent provided by the present invention has a slow-release degradation component, and the slow release of high-temperature amylase is achieved by encapsulating high-temperature amylase in polyvinyl alcohol. After release, the high-temperature amylase reacts with modified starch and other natural easily degradable components in the water-soluble swelling cementitious component, destroying the polymer macromolecular structure and degrading the polymer macromolecules into small molecules, thereby destroying the plugging layer. Since the polymer components in the plugging layer are destroyed, the plugging layer is degraded and unblocked, providing a self-unblocking function after drilling and completion operations in the depleted sandstone reservoir, without the need for unblocking operations, and achieving direct flowback and production.

[0022] 3. The water-based cementing plugging agent provided by the present invention has little effect on the density of the drilling and completion fluid system. DETAILED DESCRIPTION

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0024] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0025] The water-based cementitious plugging agent provided by the present invention is made of the following components in parts by weight: 60 to 80 parts of water-soluble swelling cementing component and 10 to 20 parts of slow-release degradation component.

[0026] Specifically, the water-soluble swelling cementing component is prepared by first modifying the surface of spherical nano-silica with aminosilane, and then reacting with modified starch, guar gum, natural rubber latex powder, and polyvinyl alcohol in sequence; Specifically, the natural rubber latex powder is prepared by freeze-drying and pulverizing natural rubber latex.

[0027] Specifically, the slow-release degradation component is prepared from polyvinyl alcohol and high-temperature amylase.

[0028] Specifically, the spherical nano-silica is one of spherical nano-silica (Changzhou Konada New Material Technology Co., Ltd.), spherical nano-silica (Shanghai Naio Nano Technology Co., Ltd.) and spherical nano-silica (Nangong Jingrui Alloy Products Co., Ltd.) or a mixture of the two in any proportion.

[0029] Specifically, the aminosilane is γ-aminopropyltriethoxysilane.

[0030] Specifically, the polyvinyl alcohol is polyvinyl alcohol powder 1788 (PVA), the molecular formula of which is C6H 10 O3.

[0031] Specifically, the modified starch is one of oxidized starch (Dezhou Runde Starch Co., Ltd.), pregelatinized modified starch (Jinan Yibo Chemical Co., Ltd.), and pregelatinized starch (Anhui Weimao Biotechnology Co., Ltd.), or a mixture of the two in any proportion.

[0032] Specifically, the guar gum is one of hydroxypropyl guar gum (Hebei Yufei Chemical Co., Ltd.), guar gum (Renqiu Litian Chemical Co., Ltd.), and locust bean gum (Wuhan Henry Biotechnology Co., Ltd.), or a mixture of the two in any proportion.

[0033] Specifically, the natural latex is one of low ammonia natural latex (Shandong Zhonghan Chemical Co., Ltd.), low ammonia natural latex (Shandong Guangju Biotechnology Co., Ltd.) and low ammonia natural latex (Shandong Shengrun Chemical Co., Ltd.), or a mixture of two of them in any proportion, and the total solid content of the natural latex is >60%.

[0034] Specifically, the high-temperature amylase is one of the following: thermostable α-amylase (Shanghai Huashang Xiangyang Biotechnology Co., Ltd.), high-temperature α-amylase (Jiangsu Jiujia Biotechnology Co., Ltd.) and α-amylase (Guangdong Mingcheng Biotechnology Co., Ltd.), or a mixture of the two in any proportion.

[0035] In addition, the present invention also provides a method for preparing a water-based cementitious plugging agent, comprising the following preparation steps: Step 1: Add 20-30 parts of natural rubber latex into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reaction kettle, add 100 parts of deionized water, add 10 to 20 parts of spherical nano-silica while stirring at 100 rpm, stir for 1 to 2 hours, then add 1 to 2 parts of aminosilane, stir at 50 rpm for 2 to 3 hours, and after sufficient reaction, dry, crush, and pass through a 2000 mesh sieve to obtain surface-modified spherical nano-silica; Step 3: Into the reactor, 10 to 20 parts of surface-modified spherical nano-silica, 20 to 30 parts of modified starch and 20 to 30 parts of guar gum are added in sequence, and stirred at 50 rpm for 2 to 3 hours. After stirring evenly, 10 to 20 parts of natural rubber latex powder are added, and stirred at 50 rpm for 2 to 3 hours. Then, the humidity in the reactor is controlled at 70% to 80%, and the mixture is cured at 50 rpm for 2 to 3 hours. Then, 20 to 30 parts of polyvinyl alcohol are added, and the mixture is stirred at 50 rpm for 2 to 3 hours. The mixture is vacuum dried at low temperature, crushed, and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: Add 100 parts of deionized water to the reactor, add 20 to 30 parts of polyvinyl alcohol while stirring at 100 rpm, and stir at room temperature for 2 to 3 hours. Then add 20 to 30 parts of high-temperature amylase, stir at room temperature for 3 to 4 hours, vacuum dry, crush, and pass through a 100-mesh sieve to obtain a slow-release degradation component; Step 5: In the reactor, add 60 to 80 parts of water-soluble swelling cementing component and 10 to 20 parts of slow-release degradation component in sequence, stir at room temperature for 2 to 3 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0036] Example 1 Step 1: Add 20 parts of low-ammonia natural rubber latex (Shandong Zhonghan Chemical Co., Ltd.) into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reactor, 100 parts of deionized water were added. Under stirring at 100 rpm, 10 parts of spherical nano-silica (Changzhou Konada New Material Technology Co., Ltd.) were added. After stirring for 1 hour, 1 part of aminosilane was added and stirred at 50 rpm for 1 hour. After sufficient reaction, the mixture was dried, crushed, and passed through a 2000 mesh sieve to obtain surface-modified spherical nano-silica. Step 3: Into the reactor, 10 parts of surface-modified spherical nano-silica, 20 parts of oxidized starch (Dezhou Runde Starch Co., Ltd.) and 20 parts of hydroxypropyl guar gum (Hebei Yufei Chemical Co., Ltd.) were added in sequence and stirred at 50 rpm for 2 h. After stirring evenly, 10 parts of natural rubber latex powder were added and stirred at 50 rpm for 2 h. The humidity in the reactor was then controlled at 70% to 80% and the mixture was cured at 50 rpm for 2 h. Then, 20 parts of polyvinyl alcohol (polyvinyl alcohol powder 1788) were added and stirred at 50 rpm for 2 h. The mixture was vacuum dried at low temperature, crushed and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: In a reaction kettle, add 100 parts of deionized water, add 20 parts of polyvinyl alcohol while stirring at 100 rpm, and stir at room temperature for 3 hours. Then add 20 parts of thermostable α-amylase (Shanghai Huashang Xiangyang Biotechnology Co., Ltd.), stir at room temperature for 3 hours, vacuum dry, crush, and pass through a 100-mesh sieve to obtain a slow-release degradation component; Step 5: In the reactor, add 60 parts of water-soluble expansion cementing component and 10 parts of slow-release degradation component in sequence, stir at room temperature for 2 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0037] Example 2 Step 1: Add 30 parts of low-ammonia natural rubber latex (Shandong Guangju Biotechnology Co., Ltd.) into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reactor, 100 parts of deionized water were added. Under stirring at 100 rpm, 20 parts of spherical nano-silica (Shanghai Naio Nano Technology Co., Ltd.) were added. After stirring for 1 hour, 2 parts of aminosilane were added and stirred at 50 rpm for 2 hours. After sufficient reaction, the mixture was dried, crushed, and passed through a 2000 mesh sieve to obtain surface-modified spherical nano-silica. Step 3: 20 parts of surface-modified spherical nano-silica, 30 parts of pregelatinized modified starch (Jinan Yibo Chemical Co., Ltd.) and 30 parts of guar gum (Renqiu Litian Chemical Co., Ltd.) were added to the reactor in sequence, and stirred at 50 rpm for 3 hours. After stirring evenly, 20 parts of natural rubber latex powder were added and stirred at 50 rpm for 2 hours. The humidity in the reactor was then controlled at 70% to 80% and the mixture was cured at 50 rpm for 3 hours. Then, 30 parts of polyvinyl alcohol were added and stirred at 50 rpm for 3 hours. The mixture was vacuum dried at low temperature, crushed and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: In a reactor, 100 parts of deionized water were added. Under stirring at 100 rpm, 30 parts of polyvinyl alcohol were added. The mixture was stirred at room temperature for 4 hours. Then, 30 parts of high-temperature α-amylase (Jiangsu Jiujia Biotechnology Co., Ltd.) were added. The mixture was stirred at room temperature for 4 hours. The mixture was vacuum-dried, crushed, and passed through a 100-mesh sieve to obtain a sustained-release degradation component. Step 5: In the reactor, add 60 parts of water-soluble expansion cementing component and 20 parts of slow-release degradation component in sequence, stir at room temperature for 3 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0038] Example 3 Step 1: Add 20 parts of low-ammonia natural rubber latex (Shandong Shengrun Chemical Co., Ltd.) into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reactor, 100 parts of deionized water were added. Under stirring at 100 rpm, 10 parts of spherical nano-silica (Nangong Jingrui Alloy Products Co., Ltd.) were added. After stirring for 1 hour, 1 part of aminosilane was added and stirred at 50 rpm for 1 hour. After sufficient reaction, the mixture was dried, crushed, and passed through a 2000 mesh sieve to obtain surface-modified spherical nano-silica. Step 3: Into the reactor, 10 parts of surface-modified spherical nano-silica, 20 parts of pregelatinized starch (Anhui Weimao Biotechnology Co., Ltd.) and 20 parts of locust bean gum (Wuhan Henry Biotechnology Co., Ltd.) were added in sequence and stirred at 50 rpm for 2 h. After stirring evenly, 10 parts of natural rubber latex powder were added and stirred at 50 rpm for 2 h. The humidity in the reactor was then controlled at 70% to 80% and the mixture was cured at 50 rpm for 2 h. Then, 20 parts of polyvinyl alcohol were added and stirred at 50 rpm for 2 h. The mixture was vacuum dried at low temperature, crushed and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: In a reaction kettle, add 100 parts of deionized water, add 20 parts of polyvinyl alcohol while stirring at 100 rpm, and stir at room temperature for 3 hours. Then add 20 parts of α-amylase (Guangdong Mingcheng Biotechnology Co., Ltd.), stir at room temperature for 3 hours, vacuum dry, crush, and pass through a 100-mesh sieve to obtain a slow-release degradation component; Step 5: In the reactor, add 70 parts of water-soluble expansion cementing component and 10 parts of slow-release degradation component in sequence, stir at room temperature for 2 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0039] Example 4 Step 1: Add 30 parts of low-ammonia natural rubber latex (Shandong Zhonghan Chemical Co., Ltd.) into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reactor, 100 parts of deionized water were added. Under stirring at 100 rpm, 20 parts of spherical nano-silica (Changzhou Konada New Material Technology Co., Ltd.) were added. After stirring for 1 hour, 2 parts of aminosilane were added and stirred at 50 rpm for 2 hours. After sufficient reaction, the mixture was dried, crushed, and passed through a 2000 mesh sieve to obtain surface-modified spherical nano-silica. Step 3: 20 parts of surface-modified spherical nano-silica, 30 parts of oxidized starch (Dezhou Runde Starch Co., Ltd.) and 30 parts of hydroxypropyl guar gum (Hebei Yufei Chemical Co., Ltd.) were added to the reactor in sequence, and stirred at 50 rpm for 3 hours. After stirring evenly, 20 parts of natural rubber latex powder were added and stirred at 50 rpm for 2 hours. The humidity in the reactor was then controlled at 70% to 80% and the mixture was cured at 50 rpm for 3 hours. 30 parts of polyvinyl alcohol was then added and stirred at 50 rpm for 3 hours. The mixture was vacuum dried at low temperature, crushed and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: In a reaction kettle, add 100 parts of deionized water, add 30 parts of polyvinyl alcohol while stirring at 100 rpm, and stir at room temperature for 4 hours. Then add 30 parts of thermostable α-amylase (Shanghai Huashang Xiangyang Biotechnology Co., Ltd.), stir at room temperature for 4 hours, vacuum dry, crush, and pass through a 100-mesh sieve to obtain a slow-release degradation component; Step 5: In the reactor, add 70 parts of water-soluble expansion cementing component and 20 parts of slow-release degradation component in sequence, and stir at room temperature for 3 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0040] Example 5 Step 1: Add 20 parts of low-ammonia natural rubber latex (Shandong Guangju Biotechnology Co., Ltd.) into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reactor, add 100 parts of deionized water, add 10 parts of spherical nano-silica (Shanghai Naion Nano Technology Co., Ltd.) while stirring at 100 rpm, stir for 1 hour, then add 1 part of aminosilane, stir at 50 rpm for 1 hour. After sufficient reaction, dry, crush, and pass through a 2000 mesh sieve to obtain surface-modified spherical nano-silica; Step 3: Into the reactor, 10 parts of surface-modified spherical nano-silica, 20 parts of pregelatinized modified starch (Jinan Yibo Chemical Co., Ltd.) and 20 parts of guar gum (Renqiu Litian Chemical Co., Ltd.) were added in sequence and stirred at 50 rpm for 2 hours. After stirring evenly, 10 parts of natural rubber latex powder were added and stirred at 50 rpm for 2 hours. The humidity in the reactor was then controlled at 70% to 80% and the mixture was cured at 50 rpm for 2 hours. Then, 20 parts of polyvinyl alcohol were added and stirred at 50 rpm for 2 hours. The mixture was vacuum dried at low temperature, crushed and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: In a reaction kettle, add 100 parts of deionized water, add 20 parts of polyvinyl alcohol while stirring at 100 rpm, and stir at room temperature for 3 hours. Then add 20 parts of high-temperature α-amylase (Jiangsu Jiujia Biotechnology Co., Ltd.), stir at room temperature for 3 hours, vacuum dry, crush, and pass through a 100-mesh sieve to obtain a slow-release degradation component; Step 5: In the reactor, add 80 parts of water-soluble expansion cementing component and 10 parts of slow-release degradation component in sequence, stir at room temperature for 2 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0041] Example 6 Step 1: Add 30 parts of low-ammonia natural rubber latex (Shandong Shengrun Chemical Co., Ltd.) into a reactor, freeze-dry at low temperature, and grind through a 100-mesh sieve to obtain natural rubber latex powder; Step 2: In a reactor, 100 parts of deionized water were added. Under stirring at 100 rpm, 20 parts of spherical nano-silica (Nangong Jingrui Alloy Products Co., Ltd.) were added. After stirring for 1 hour, 2 parts of aminosilane were added and stirred at 50 rpm for 2 hours. After sufficient reaction, the mixture was dried, crushed, and passed through a 2000 mesh sieve to obtain surface-modified spherical nano-silica. Step 3: 20 parts of surface-modified spherical nano-silica, 30 parts of oxidized starch (Dezhou Runde Starch Co., Ltd.) and 30 parts of locust bean gum (Wuhan Henry Biotechnology Co., Ltd.) were added to the reactor in sequence and stirred at 50 rpm for 3 hours. After stirring evenly, 20 parts of natural rubber latex powder were added and stirred at 50 rpm for 2 hours. The humidity in the reactor was then controlled at 70% to 80% and the mixture was cured at 50 rpm for 3 hours. Then, 30 parts of polyvinyl alcohol were added and stirred at 50 rpm for 3 hours. The mixture was vacuum dried at low temperature, crushed and passed through a 100-mesh sieve to obtain a water-soluble swelling binder component. Step 4: In a reaction kettle, 100 parts of deionized water were added. Under stirring at 100 rpm, 30 parts of polyvinyl alcohol were added. The mixture was stirred at room temperature for 4 hours. Then, 30 parts of α-amylase (Guangdong Mingcheng Biotechnology Co., Ltd.) were added. The mixture was stirred at room temperature for 4 hours. The mixture was vacuum dried, crushed, and passed through a 100-mesh sieve to obtain a sustained-release degradation component. Step 5: In the reactor, add 80 parts of water-soluble expansion cementing component and 20 parts of slow-release degradation component in sequence, stir at room temperature for 3 hours under the stirring condition of 10 rpm to obtain a water-based cementing plugging agent.

[0042] Comparative Example 1 The only difference from Example 1 is that no natural rubber latex is added in this comparative example.

[0043] Comparative Example 2 The only difference from Example 1 is that no spherical nano-silica is added in this comparative example.

[0044] Comparative Example 3 The only difference from Example 1 is that no modified starch is added in this comparative example.

[0045] Comparative Example 4 The only difference from Example 1 is that guar gum is not added in this comparative example.

[0046] Comparative Example 5 The only difference from Example 1 is that no high-temperature amylase is added in this comparative example.

[0047] Comparative Example 6 The only difference from Example 1 is that polyvinyl alcohol is not added in this comparative example.

[0048] The water-based cementitious plugging agents prepared in the examples and the comparative examples are evaluated as follows: 1. Instruments for evaluating water-based cementing plugging agents: The instruments used include a density meter (Qingdao Haitongda Special Instrument Co., Ltd.), a ZNN-D6 six-speed rotational viscometer (Qingdao Haitongda Special Instrument Co., Ltd.), a GJSS-B12K variable frequency high-speed mixer (Qingdao Haitongda Special Instrument Co., Ltd.), a GGS71-A high-temperature and high-pressure water loss meter (Qingdao Haitongda Special Instrument Co., Ltd.), a bonding strength tester (Hubei Hanke New Technology Co., Ltd.), and a precision electronic scale (accuracy 0.01g).

[0049] 2. Formula of base slurry and embodiment: Base slurry (blank sample) formula: 300ml seawater + 0.6Na2CO3 + 0.6gNaOH + 0.6g viscosity enhancer PF-HVIS + 3g fluid loss reducer PF-FLO HT + 9gKCl.

[0050] The sample slurry formula of the embodiment and comparative example is: base slurry + 15g water-based cementitious plugging agent.

[0051] 3. Preparation methods of base slurry, sample slurries of examples and comparative examples: Preparation of the base slurry: (1) Measure 300 ml of seawater and pour it into a high-stirring cup. Weigh 0.6 g of Na2CO3 and 0.6 g of NaOH and add them to the high-stirring cup. Stir at 10,000 r / min for 2 min. (2) Weigh 0.6 g of PF-HVIS, a thickener, and slowly add it to the high-stirring cup at 10,000 r / min. Stir at high speed for 20 min after adding the thickener. (3) Weigh 3 g of PF-FLO HT, a fluid loss reducer, and 9 g of KCl and add them to the high-stirring cup. Stir at 10,000 r / min for 20 min. The base slurry sample was obtained through the above steps.

[0052] Preparation method of the embodiment and comparative example: 300 ml of base slurry was measured, 15 g of water-based cementitious plugging agent was added under stirring conditions of 10,000 r / min, and high stirring was carried out for 5 minutes. The sample slurries of the embodiment and comparative example were obtained through the above steps.

[0053] 4. Performance evaluation method: Steps for determining density performance parameters: In accordance with GB / T 16783.1-2014, the evaluation sample was tested for density at room temperature using a density meter.

[0054] Bond strength test method: (1) Weigh 200g of quartz sand with a mesh size of 40-80 using a precision electronic scale, pour it into the water loss bucket of the high-temperature and high-pressure water loss instrument, and compact the sand body. The compacted sand body is used as the evaluation medium "sand body" for measuring the bonding strength and sealing pressure bearing capacity; (2) Measure 300 ml of base slurry, sample slurry of the embodiment and comparative example, slowly pour them into the water loss bucket of the high-temperature and high-pressure water loss instrument, seal it, install the pressurized pipeline, raise the temperature to 80 ° C, open the lower drain valve, and increase the pressure to 3.5 MPa. When filtrate is found to flow out of the drain valve, immediately close the drain valve and maintain it at a constant temperature of 80 ° C for 1 hour. After the curing time is up, cool the water loss bucket to room temperature and carefully release the pressure. After disassembly, carefully remove the "sand body" and measure its bonding strength (Pa) with a bonding strength tester. Record the experimental data; (3) Measure 300 ml of the base slurry, sample slurry of the embodiment, and sample slurry of the comparative example and slowly pour them into the dehydration bucket of the high-temperature and high-pressure dehydration apparatus. Seal the slurry, install the pressurization pipeline, raise the temperature to 80°C, and pressurize at 1 MPa for constant temperature curing. After curing for 10 hours, open the lower drain valve and then pressurize with nitrogen starting from 0 MPa. Each pressurization step is 0.5 MPa, with the maximum test pressure difference of 8 MPa. Gradually increase the pressure and record the pressure bearing capacity. Similarly, measure the pressure bearing capacity after curing for 72 hours. The pressure bearing capacity unit is MPa.

[0055] Table 1 shows the performance evaluation results of the water-based cementitious plugging agents prepared in Examples 1-6 and Comparative Examples 1-6.

[0056] Table 1 Performance evaluation results of water-based cementitious plugging agents prepared in Examples 1-6 and Comparative Examples 1-6

[0057] It can be seen from the data in Table 1 that: compared with the base slurry, the density of the sample slurries of the embodiment and the comparative example does not change much, the bonding strength increases, and the pressure bearing capacity increases.

[0058] The specific analysis is as follows: (1) The bonding strength of the base slurry is 364 Pa, indicating that the bonding strength of the sand body cured by the base slurry is low; it leaks when pressurized to 0.5 MPa, indicating that the base slurry is not pressure-bearing.

[0059] (2) The performance data of the sample slurries of the water-based cementitious plugging agents prepared in Examples 1 to 6 show that the density changes very little, and the pressure bearing capacity is significantly improved to 7-8 MPa. After 72 hours of curing, leakage occurs when the pressure is increased to 0.5 MPa, indicating that the self-releasing effect of the plugging is good.

[0060] (3) The performance data of the sample slurries of the water-based cementitious plugging agents prepared from Comparative Examples 1 to 6 show that the only difference from Example 1 is that the comparative examples do not add the single components of natural rubber latex, spherical nano-silica, modified starch, guar gum, high-temperature amylase, and polyvinyl alcohol.

[0061] In comparative example 1, natural latex was removed, and the sand body strength and pressure bearing performance after curing for 10 hours decreased; in comparative example 2, spherical nano-silica was removed, and the sand body strength decreased, and the pressure bearing performance after curing for 10 hours decreased significantly; in comparative example 3, modified starch was removed, and the sand body strength and pressure bearing performance after curing for 10 hours decreased; in comparative example 4, guar gum was removed, and the sand body strength and pressure bearing performance after curing for 10 hours decreased; in comparative example 5, high-temperature amylase was removed, and the pressure bearing capacity after curing for 72 hours was 8 MPa, indicating that the degradation effect of high-temperature amylase was lacking and the plugging layer was not damaged; in comparative example 6, polyvinyl alcohol was removed. Due to the lack of the inhibitory effect of polyvinyl alcohol, the high-temperature amylase directly reacted with the modified starch and other polymers, and the pressure bearing capacity after curing for 10 hours was only 1.5 MPa. From the above, it can be seen that when the prepared water-based cementitious plugging agent lacks any one of the components of natural rubber latex, spherical nano-silica, modified starch, guar gum, high-temperature amylase, and polyvinyl alcohol, the performance of the sample slurry system in terms of sand body bonding strength, 10-h curing pressure bearing performance, and 72-h curing pressure bearing performance is significantly reduced, indicating that the above components directly affect the use effect of the water-based cementitious plugging agent.

[0062] Comparison between the comparative examples and the examples above shows that natural rubber latex, spherical nano-silica, modified starch, guar gum, high-temperature amylase, and polyvinyl alcohol are all main components for preparing the water-based cementitious plugging agent.

[0063] The main functions of the main components of the water-based cementitious plugging agent of the present invention are: using natural latex to enhance the cementing performance through its viscoelasticity and adsorption bonding properties, using spherical nano-silica to provide a rigid support structure to improve the plugging quality and pressure bearing capacity, using modified starch to enhance the fluid loss control ability, using guar gum to enhance the spatial structure and cementing performance through hydrogen bonding force, using high-temperature amylase to provide the function of degrading modified starch and other natural polymer components at high temperature, and using polyvinyl alcohol to provide a surface coating of a water-soluble swelling cementing component and a slow-release degradation component, thereby controlling the degradation reaction rate between the high-temperature amylase and the modified starch and other natural polymer components.

[0064] The action mechanism of the water-based cementitious plugging agent of the present invention is divided into two stages. In the first stage, after being added to the drilling and completion fluid system, the water-based cementitious plugging agent enters the underground formation reservoir as the drilling circulation system, forming a plug in the sandstone reservoir. Under the hydration action, the water-soluble swelling cementing component of the water-based cementitious plugging agent is gradually hydrated, wherein the viscoelasticity, rigidity, and hydration swelling components in the water-soluble swelling cementing component form a stable cementitious plugging layer through hydration bonding and cementation, thereby preventing leakage and reducing reservoir damage, and providing good cementitious plugging pressure bearing performance for a period of time; in the second stage, under reservoir temperature conditions, the polyvinyl alcohol film on the surface of the water-soluble swelling cementing component and the slow-release degradation component is gradually dissolved and destroyed, and the high-temperature amylase is gradually released and degrades with the modified starch and other natural polymer components of the water-soluble swelling cementing component. The polymer is degraded into small molecules, which eventually destroys the cementing structure of the plugging layer, and finally the plugging layer is released, thereby achieving dredging of the oil and gas channels in the reservoir and further achieving safe production.

[0065] Through the above principles and effects, the water-based cementitious plugging agent of the present invention achieves the purpose of improving the cementation strength of sandstone formation rocks and improving the sealing pressure bearing capacity. Therefore, the lack of any main component will lead to a decrease in the sealing, leak-proofing and reservoir protection performance of the water-based cementitious plugging agent.

Claims

1. A water-based cementing plugging agent for depleted sandstone reservoirs, comprising the following components by weight: 60-80 parts of water-soluble swelling cementing component and 10-20 parts of slow-release degradation component; The water-soluble swelling cementing component is prepared from surface-modified spherical nano-silica, modified starch, guar gum, natural rubber latex powder and polyvinyl alcohol; The slow-release degradation component is prepared from polyvinyl alcohol and high-temperature amylase.

2. The water-based cementitious plugging agent according to claim 1, characterized in that: The surface-modified spherical nano-silica is obtained by surface-modifying spherical nano-silica with aminosilane; The aminosilane is γ-aminopropyltriethoxysilane.

3. The water-based cementitious plugging agent according to claim 1 or 2, characterized in that: The modified starch is one of oxidized starch, pregelatinized modified starch and pregelatinized starch, or a mixture of the two in any proportion; The guar gum is one of hydroxypropyl guar gum, guar gum and locust bean gum, or two of them mixed in any proportion.

4. The water-based cementitious plugging agent according to any one of claims 1 to 3, characterized in that: The natural latex is one of low ammonia natural latex, low ammonia natural latex and low ammonia natural latex, or a mixture of the two in any proportion, and the total solid content is greater than 60%.

5. The water-based cementitious plugging agent according to any one of claims 1 to 4, characterized in that: The natural rubber latex powder is obtained by freeze-drying and crushing natural rubber latex; The high-temperature amylase is a high-temperature resistant α-amylase.

6. A method for preparing the water-based cementitious plugging agent according to any one of claims 1 to 5, comprising the following steps: S1. Surface-modified spherical nano-silica, modified starch, and guar gum are mixed, natural rubber latex powder is added, and curing is performed, and finally polyvinyl alcohol is added and stirred to obtain a water-soluble swelling cementitious component; S2, mixing polyvinyl alcohol with high-temperature amylase to obtain a slow-release degradation component; S3, mixing the water-soluble swelling cement component and the slow-release degradation component.

7. The preparation method according to claim 6, characterized in that: The natural rubber latex powder is obtained by freeze-drying and crushing natural rubber latex; The freeze-drying temperature is -30°C to -10°C.

8. The preparation method according to claim 6 or 7, characterized in that: Step S1 specifically includes the following steps: The surface-modified spherical nano-silica, the modified starch and the guar gum are added to the reactor in sequence and stirred for 2 to 3 hours. After stirring evenly, the natural rubber latex powder is added and stirred for 2 to 3 hours. The humidity in the reactor is then controlled to be 70% to 80%, and the mixture is cured under stirring for 2 to 3 hours. The polyvinyl alcohol is then added and stirred for 2 to 3 hours. The mixture is vacuum dried and crushed at low temperature and passed through a 100-mesh sieve to obtain the water-soluble swelling binder component.

9. The preparation method according to any one of claims 6 to 8, characterized in that: Step S2 specifically includes the following steps: Deionized water was added to the reactor, and the polyvinyl alcohol was added under stirring, and the mixture was stirred at room temperature for 2 to 3 hours. The high-temperature amylase was then added, and the mixture was stirred at room temperature for 3 to 4 hours. The mixture was vacuum dried, crushed, and passed through a 100-mesh sieve to obtain the slow-release degradation component.

10. Use of the water-based cementitious plugging agent according to any one of claims 1 to 5 in drilling and completion of shallow oil and gas formations in oil and gas fields; in, The shallow oil and gas layer is a sandstone formation with a temperature of 70 to 100°C.

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