Leaking stoppage cement paste for weak cementation layer as well as preparation method and application of leaking stoppage cement paste

Abstract

The invention discloses leaking stoppage cement paste for a weak cementation layer as well as a preparation method and application of the leaking stoppage cement paste. The cement paste is prepared from the following components in parts by mass: 100 parts of cement, 0.2-1.2 parts of a leaking stoppage material, 2-6 parts of a fluid loss agent, 0.2-1.5 parts of a dispersing agent, 0.1-0.6 part of a defoaming agent and 40-50 parts of water. The preparation method of the cement paste comprises the following steps: 1) mixing the cement, the leaking stoppage material, the fluid loss agent and the dispersing agent in parts by mass to obtain a solid mixture; 2) mixing water and a defoaming agent according to a mass ratio to prepare slurry preparation water; and (3) adding the solid mixture into slurry preparation water which is stirred at a low speed, and stirring at a high speed after the solid mixture is added, thereby obtaining the cement slurry for leaking stoppage. The leaking stoppage cement paste for the weak cementation layer is applied to preparation of weak cementation layer materials for well cementation of oil and gas wells. The system improves the plugging performance of the cement paste, reduces the leakage risk in the well cementation process, improves the cementing strength of the first interface and the second interface of well cementation, and ensures the well cementation quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas well cement slurry system, and relates to a weakly cemented layer plugging cement slurry as well as a preparation method and application thereof. BACKGROUND

[0002] With the deepening of domestic and foreign oilfield drilling and the increasing complexity of drilled formations, more and more losses occur in the drilling process. Since the cemented well section is getting longer, combined with the uncertainty of the formation leakage point and the unclearness of the leakage mechanism, although the formation pressure bearing capacity is improved by plugging before cementing, serious loss often occurs during the cementing process, which causes low return of the cement slurry, and in severe cases, the annular loss is large, the slurry column pressure drops, the formation fluid cannot be pressed, and the wellhead is under pressure or even blowout is induced. In addition, the cement sheath is easily cracked and fractured, and thus damaged, especially the presence of drilling fluid cake, which can further exacerbate the expansion and development of the annulus. Although the drilling fluid cake can play a role in reducing filtration loss, preventing collapse and protecting oil and gas reservoirs during drilling construction, the strong inhibition of the drilling fluid single agent also promotes the aggregation and accumulation of solid particles. After the free water is lost and evaporated, there will be a thick cake on the well wall. Since the components of the cake are mixed and not cemented together by chemical or physical action, but only squeezed and stacked together, the cake structure is chaotic and has low strength. The cake is sandwiched between the cement sheath and the formation, and the cement sheath is difficult to contact the formation directly. The cake and the formation have relatively high bonding strength due to the accumulation of solid particles and the relatively dense structure. The bonding interface between the cake and the cement sheath is a virtual cake layer, which has chaotic structure and many pores, and is the main part of the fracture formed at the second interface during cementing. The cake, the formation and the cement sheath are difficult to form an effective cementing whole, and the cement sheath sealing system cannot function, which leads to a series of problems and accidents, and the late oil and gas production cannot be guaranteed.

[0003] The current main solution is to take measures to plug the pressure loss of the formation, adopt the near-balance pressure cementing process, use the matching spacer fluid, and reduce the pressure excitation in the casing and well. However, the cementing quality is still not ideal. Especially for the pore-type low-pressure formation, the leakage-type formation and the induced fractured formation, the low return of the cement slurry during cementing has always been a major technical problem affecting the cementing quality. The use of low-density cement slurry has a certain effect on leakage prevention, but it has defects such as high volume shrinkage, high brittleness, low compressive strength, poor stability of the cement slurry system, and cannot completely and effectively prevent leakage and improve the quality of the cement sheath in the later cementing period. How to reduce the loss during drilling and improve the cementing quality of the middle and late oil and gas wells is a major problem faced by current oil and gas drilling engineering, and is an important measure to improve the service life of oil wells and ensure stable and high production.

[0004] The cement slurry with the fiber and the elastic particle material can prevent the cement slurry from leaking in the cementing process, ensure the cement slurry to return to the designed position, and play a good plugging and cementing effect. For the current numerous natural fibers and artificial fibers, the polypropylene fiber is a high-strength polypropylene bundle-shaped monofilament fiber. For a larger slit, it is difficult to realize plugging by only inserting the fiber into the slit, because the directly inserted fiber can completely enter the slit and cannot be left outside the slit, and has a certain negative impact on the viscosity, fluidity, compressive strength and flexural strength of the cement stone, which cannot guarantee the safe production of the oil and gas well and causes huge economic losses. Therefore, a plugging cement slurry system is urgently needed. SUMMARY

[0005] The purpose of the present application is to provide a plugging cement slurry for weak cementation layer and a preparation method and application thereof.

[0006] The system improves the plugging performance of the cement slurry, reduces the leakage risk in the cementing process, and improves the cementing strength of the first and second interfaces of the cement slurry, thereby ensuring the cementing quality.

[0007] The present application provides a plugging cement slurry for weak cementation layer, which is prepared from the following components by mass fraction: 100 parts of cement, 0.2-1.2 parts of plugging material, 2-6 parts of fluid loss reducer, 0.2-1.5 parts of dispersing agent, 0.1-0.6 parts of defoaming agent, and 40-50 parts of water.

[0008] In the present application, the plugging cement slurry for weak cementation layer is specifically prepared from the following components by mass fraction: (1) 100 parts of cement, 0.2 parts of plugging material, 3 parts of fluid loss reducer, 0.3 parts of dispersing agent, 0.2 parts of defoaming agent, and 42 parts of water; (2) 100 parts of cement, 0.4 parts of plugging material, 5 parts of fluid loss reducer, 0.6 parts of dispersing agent, 0.6 parts of defoaming agent, and 44 parts of water; (3) 100 parts of cement, 0.6 parts of plugging material, 4 parts of fluid loss reducer, 0.8 parts of dispersing agent, 0.3 parts of defoaming agent, and 44 parts of water; (4) 100 parts of cement, 0.8 parts of plugging material, 2 parts of fluid loss reducer, 1.2 parts of dispersing agent, 0.5 parts of defoaming agent, and 46 parts of water.

[0009] In the above cement slurry, the plugging material is aluminum silicate fiber.

[0010] In the present application, the aluminum silicate fiber has high toughness and moderate length, can be well dispersed in the cement slurry, is suitable for the plugging cement slurry system, and is used as the core component to prepare the cement slurry for plugging with good compatibility with cement, which can effectively improve the leakage performance of the weak cementation layer cement slurry and improve the cementing strength of the first and second interfaces of the cement slurry.

[0011] The density of the aluminum silicate fiber in the cement slurry can be 0.08-0.18 g / cm 3 , the length can be 6.5 mm, the average particle size can be 2-3 μm, the elastic modulus can be 200-430 GPa, the tensile strength can be 1500-3500 MPa, and the ultimate elongation can be 1-2%, and specifically can be aluminum silicate fiber commercially available from Chengdu Jinxiang Technology Co., Ltd.

[0012] The cement in the cement slurry can be G-grade oil well cement or Portland cement, both of which are the most commonly used cements in oil and gas well cementing construction.

[0013] The fluid loss additive in the cement slurry can be AMPS type fluid loss additive G33S, and specifically can be G33S commercially available from Henan Weihui City Chemical Co., Ltd.

[0014] The dispersant in the cement slurry can be polycarboxylic acid dispersant USZ, and specifically can be USZ commercially available from Henan Weihui City Chemical Co., Ltd.

[0015] In the present application, the AMPS (2-acrylamido-2-methylpropanesulfonic acid) type fluid loss additive can withstand temperatures up to 200 °C or higher, and the sulfonic acid group can still maintain hydration capacity at high temperatures. Compared with traditional fluid loss additives (such as hydrolyzed polyacrylonitrile HPAM), AMPS type products can still maintain viscosity and filtration control ability at high temperatures. The AMPS type fluid loss additive has excellent compatibility with the polycarboxylic acid dispersant, and is not prone to precipitation or antagonistic effect when used together, and is suitable for high-performance cement slurry systems.

[0016] The defoaming agent in the cement slurry can be SXY-2, and specifically can be SXY-2 commercially available from Henan Weihui City Chemical Co., Ltd.

[0017] The present application also provides a preparation method of the weakly cemented layer plugging cement slurry, which comprises the following steps: 1) mixing the cement, the plugging material, the fluid loss additive, and the dispersant according to the mass fraction to obtain a solid mixture; 2) mixing the water and the defoaming agent according to the mass fraction to prepare a slurry water; 3) adding the solid mixture to the low-speed stirring slurry water, and then high-speed stirring after the addition is completed, to obtain the weakly cemented layer plugging cement slurry.

[0018] In the preparation method, the time for adding the solid mixture to the slurry water can be 10-20 s, and specifically can be 12 s, 14 s, or 15 s. The low-speed stirring rate can be 4000±200 rpm.

[0019] In the preparation method, the rate of the high-speed stirring can be 12000±200 rpm, specifically 12200 rpm, and the time can be 30-40 s, specifically 35 s, 36 s or 38 s.

[0020] The weakly cemented layer plugging cement slurry provided by the application is applied to the preparation of a weakly cemented layer material for well cementing of oil and gas wells.

[0021] The application has the following beneficial effects: (1) The weakly cemented layer plugging cement slurry system provided by the application uses aluminum silicate fiber as a plugging material, which is wound and gathered in the joint gap to form a mesh structure, so that the cement slurry particles change direction multiple times and reduce the flow rate, and finally accumulate in the mesh hole smaller than the diameter of the particles to plug the joint gap.

[0022] (2) The weakly cemented layer plugging cement slurry system provided by the application uses aluminum silicate fiber which is almost not affected by temperature and can be well dispersed in the cement slurry without affecting the density, thickening time and rheological property, thereby improving the cementing strength of the first and second interfaces and simplifying the system formula and facilitating construction.

[0023] (3) The weakly cemented layer plugging cement slurry system provided by the application improves the plugging performance of the cement slurry and reduces the risk of leakage during the working process, and can meet the requirements of strict cementing operations for preventing gas channeling and integrity of the cement stone in deep wells, ultra-deep wells, low-pressure leaky wells and other wells, that is, the system can long-term seal and cement the long sealing and cementing section of the leaky well and reduce the occurrence of gas channeling. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the thickening curve diagram of the comparative example of 90 °C x 45 MPa x 45 min.

[0025] Figure 2 is the thickening curve diagram of Example 1 of 90 °C x 45 MPa x 45 min.

[0026] Figure 3 is the thickening curve diagram of Example 2 of 90 °C x 45 MPa x 45 min.

[0027] Figure 4 is the thickening curve diagram of Example 3 of 90 °C x 45 MPa x 45 min.

[0028] Figure 5 is the thickening curve diagram of Example 4 of 90 °C x 45 MPa x 45 min.

[0029] Figure 6are the interface cementation strength test results of the comparative example and examples 1-4.

[0030] Figure 7 are the interface cementation strength test results of the comparative example and examples 1-4. DETAILED DESCRIPTION

[0031] The present application is further illustrated below in accordance with the accompanying drawings and examples in order to facilitate the understanding of the present application for those skilled in the art. However, it should be clear that the present application is not limited to the scope of the specific embodiments, and any changes within the spirit and scope of the present application as defined and determined by the appended claims are within the protection of the present application for those skilled in the art.

[0032] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0033] The materials, reagents, etc. used in the following examples can be obtained commercially unless otherwise specified.

[0034] In the following examples, the fluid loss additive is AMPS-based fluid loss additive G33S, which is commercially available from Henan Weihui City Chemical Co., Ltd.; The dispersant is polycarboxylic acid dispersant USZ, which is commercially available from Henan Weihui City Chemical Co., Ltd.; The defoaming agent is SXY-2, which is commercially available from Henan Weihui City Chemical Co., Ltd.

[0035] Example 1 (1) Dry mixture preparation: an electronic balance was used to weigh Jiahua G-grade oil well cement 100 parts, plugging material aluminum silicate fiber 0.2 parts, AMPS-based fluid loss additive G33S 3 parts, and polycarboxylic acid dispersant 0.3 parts according to the mass ratio, and the mixture was mixed uniformly to prepare the dry mixture.

[0036] (2) Slurry water preparation: an electronic balance was used to weigh defoaming agent 0.2 parts and water 42 parts according to the mass ratio, and the mixture was mixed uniformly to prepare the slurry water.

[0037] (3) Preparation of plugging cement slurry: a high-speed mixer was used for mixing, with a fixed speed of about 4000 rpm, and the mixed solid dry mixture was poured into the slurry cup with slurry water within 12 s, the cup cover was covered, the speed was adjusted to high speed, i.e. 12200 rpm, and the mixture was mixed for 38 s to obtain the plugging cement slurry.

[0038] Example 2 (1) Dry mixture preparation: an electronic balance was used to weigh Jiahua G-grade oil well cement 100 parts, plugging material aluminum silicate fiber 0.4 parts, AMPS-based fluid loss additive 5 parts, and polycarboxylic acid dispersant 0.6 parts according to the mass ratio, and the mixture was mixed uniformly to prepare the dry mixture.

[0039] (2) Preparation of the mixing water: using an electronic balance to weigh 0.4 parts of the defoaming agent and 44 parts of water according to the mass ratio, and mixing them uniformly to obtain the mixing water.

[0040] (3) Preparation of the plugging cement slurry: using a high-speed mixer to mix, fixing the rotating speed at about 4200 rpm, pouring the mixed solid dry mixture into the slurry cup with the mixing water within 14 s, covering the cup cover, adjusting the rotating speed to high speed, i.e. 12100 rpm, mixing for 36 s, and uniformly mixing to obtain the plugging cement slurry system.

[0041] Example 3 (1) Preparation of the dry mixture: using an electronic balance to weigh 100 parts of Jiahua G-grade oil well cement, 0.6 parts of the plugging material aluminum silicate fiber, 4 parts of the AMPS type fluid loss reducer, and 0.8 parts of the polycarboxylic acid dispersant according to the mass ratio, and mixing them uniformly to obtain the dry mixture.

[0042] (2) Preparation of the mixing water: using an electronic balance to weigh 0.3 parts of the defoaming agent and 44 parts of water according to the mass ratio, and mixing them uniformly to obtain the mixing water.

[0043] (3) Preparation of the plugging cement slurry: using a high-speed mixer to mix, fixing the rotating speed at about 4200 rpm, pouring the mixed solid dry mixture into the slurry cup with the mixing water within 14 s, covering the cup cover, adjusting the rotating speed to high speed, i.e. 12100 rpm, mixing for 36 s, and uniformly mixing to obtain the plugging cement slurry system.

[0044] Example 4 (1) Preparation of the dry mixture: using an electronic balance to weigh 100 parts of Jiahua G-grade oil well cement, 0.8 parts of the plugging material aluminum silicate fiber, 2 parts of the AMPS type fluid loss reducer, and 1.2 parts of the polycarboxylic acid dispersant according to the mass ratio, and mixing them uniformly to obtain the dry mixture.

[0045] (2) Preparation of the mixing water: using an electronic balance to weigh 0.5 parts of the defoaming agent and 46 parts of water according to the mass ratio, and mixing them uniformly to obtain the mixing water.

[0046] (3) Preparation of the plugging cement slurry: using a high-speed mixer to mix, fixing the rotating speed at about 4200 rpm, pouring the mixed solid dry mixture into the slurry cup with the mixing water within 14 s, covering the cup cover, adjusting the rotating speed to high speed, i.e. 12100 rpm, mixing for 36 s, and uniformly mixing to obtain the plugging cement slurry system.

[0047] Comparative Example 1 The comparative example is a blank control group without adding the plugging material.

[0048] (1) Dry mixture preparation: using an electronic balance to weigh Jiahua G-grade oil well cement 100 parts, AMPS type fluid loss reducer 3 parts and polycarboxylic acid dispersing agent 0.4 parts according to the mass ratio, and mixing them uniformly to prepare the dry mixture.

[0049] (2) Slurry water preparation: using an electronic balance to weigh the air-entraining agent 0.2 parts and water 44 parts according to the mass ratio, and mixing them uniformly to prepare the slurry water.

[0050] (3) Preparation of blank control group cement slurry: using a high-speed mixer to mix, fixing the rotation speed at about 4000 rpm, pouring the mixed solid dry mixture into the slurry cup with slurry water within 13 s, covering the cup cover, adjusting the rotation speed to high speed, i.e. 12000 rpm, mixing for 37 s, and uniformly mixing to obtain the blank control group cement slurry.

[0051] Example 5, performance test of different cement slurry systems The cement slurries prepared in the above Comparative Example 1 and Examples 1-4 of the application were subjected to density, fluidity, loss amount, thickening, and compressive strength, tensile strength, and interfacial cementing strength experiments according to the “Oil Well Cement Application Performance Test Method” (SY / T 5546-92), “Oil Well Cement” (GB 10238-2005), “Oil Well Cement Test Recommended Practice” (API RP10B), and “Oil Well Cement Test Method” (GB / T 19139-2012).

[0052] The density and fluidity were at room temperature; the API fluid loss condition was 6.9 MPa x 90 °C; the thickening condition was 90 °C x 45 MPa x 45 min; the tensile and compressive strength experiment condition was 20 MPa x 150 °C for 24 h curing; and the interfacial cementing strength experiment condition was 70 °C, normal pressure curing for 1, 2, and 3 d. The experimental results are shown in Table 1.

[0053] The cement slurry prepared in the above Comparative Example 1 was named T0; Examples 1-4 were named T 0.2 , T 0.4 , T 0.6 , and T 0.8 , respectively.

[0054] Table 1 Performance test results of cement slurry systems of Comparative Example and Examples 1-4

[0055] As shown in Table 1, the fluidity, API water loss, flexural strength, and compressive strength of the slurry prepared using different weak cementing layers all meet the requirements for cementing operations. Adding aluminosilicate fibers to the cement slurry did not significantly change the slurry's rheological properties. Different dosages of aluminosilicate fibers shortened the thickening time of the cement slurry, but still met the cementing requirements. The system formulation is simple, requiring only three admixtures to construct the plugging cement slurry system. Compared to Comparative Example 1, the API water loss in Examples 1-4 of this invention was reduced, indicating that the plugging cement slurry system of this invention can effectively improve the plugging performance of cement slurry and reduce the risk of leakage during operation. When the dosage of aluminosilicate fibers increased within the range of 0-0.6%, the flexural and compressive strengths of the cement stone both increased. When the dosage increased to 0.6%, the flexural and compressive strengths decreased, but overall, the flexural strength of the cement stone increased to varying degrees.

[0056] The thickening experimental curves of Comparative Example 1 and Examples 1-4 are as follows: Figures 1-5 As shown; the experimental results of the cemented interface are as follows. Figures 6-7 As shown.

[0057] Depend on Figures 6-7 It can be seen that, compared with Comparative Example 1, the bonding strength of the cementing interface between the first and second interfaces of the weak cementing layer plugging cement slurry system of the present invention is improved, and the bonding effect between the plugging material (aluminosilicate fiber) and the cement stone is generally better with the increase of curing time. Example 3 (T 0.6 The bonding strength enhancement effect of the cement stone at the first and second interfaces of the 3-day cement stone cementing increased by 48.1% and 21.0% respectively compared with the comparative example. Alumina silicate fibers are almost unaffected by temperature, and their moderate length allows for good dispersion in the cement slurry. In the weak cementing layer plugging cement slurry system provided by this invention, the alumina silicate fibers intertwine with each other at the joint, accumulating and blocking pores. Simultaneously, the fiber layers form a network structure, forcing cement slurry particles to change direction and reduce flow velocity multiple times, ultimately accumulating at mesh openings smaller than their diameter, sealing the joint and preventing leakage. This can meet the stringent requirements for gas channeling prevention and integrity of cement stone in cementing operations such as deep wells, ultra-deep wells, and low-pressure, easily leaking wells, sealing long-term leaking sections. It can not only provide long-term sealing for oil and gas wells in easily leaking wells and seal long-term leaking sections, but also reduce the occurrence of gas channeling.

Claims

1. A lost circulation cement slurry for use in weakly cemented formations, characterized in that, The cement slurry is prepared by the following components in mass fraction: 100 parts of cement, 0.2-1.2 parts of plugging material, 2-6 parts of fluid loss additive, 0.2-1.5 parts of dispersant, 0.1-0.6 parts of defoaming agent, and 40-50 parts of water.

2. The cement paste according to claim 1, characterized in that, The plugging material is aluminum silicate fiber.

3. The cement paste according to claim 2, characterized in that, The density of the aluminum silicate fiber is 0.08-0.18 g / cm 3 , the length is 6.5 mm, the average particle size is 2-3 μm, the elastic modulus is 200-430 GPa, the tensile strength is 1500-3500 MPa, and the ultimate elongation is 1-2%.

4. Cement paste according to any one of claims 1 - 3, characterized in that, The cement is G-grade oil well cement or Portland cement.

5. The cement slurry of any of claims 1-4, wherein, The fluid loss additive is AMPS fluid loss additive G33S.

6. The cement slurry of any of claims 1-5, wherein, The dispersant is polycarboxylic acid dispersant USZ. The defoaming agent is SXY-2.

7. A method for preparing the plugging cement slurry for weak cementing layer according to any one of claims 1-6, comprising the following steps: 1) mixing the cement, the plugging material, the fluid loss additive, and the dispersant according to the mass ratio to obtain a solid mixture; 2) mixing the water and the defoaming agent according to the mass ratio to prepare a mixing water; 3) adding the solid mixture into the mixing water under low-speed stirring, and then high-speed stirring after the addition is completed, to obtain the plugging cement slurry for weak cementing layer.

8. The preparation method according to claim 7, characterized in that, The time for adding the solid mixture into the mixing water is 10-20 s; The low-speed stirring rate is 4000±200 rpm.

9. The production method according to claim 7 or 8, characterized by, The high-speed stirring rate is 12000±200 rpm, and the time is 30-40 s.

10. The plugging cement slurry for weak cementing layer according to any one of claims 1-6 in the preparation of weak cementing layer material for oil and gas well cementing.

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