Low density cement slurries, methods of making and using same

Abstract

The present application relates to the technical field of cement-based cementing material, and particularly relates to a low-density cement slurry, a preparation method and application thereof, which adopts oil well cement as a cementing material, adds desert sand, rice husk ash and modified silica sol, and adds a functional additive, and then adopts a high water-binder ratio to prepare a low-density cement slurry with good stability and high mechanical performance without adding an additional lightening agent, and the low-density cement slurry can be used in medium-high temperature cementing engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cement-based cementing materials, in particular to a low-density cement slurry and a preparation method and application thereof. BACKGROUND

[0002] Oil and gas exploitation engineering needs to be cemented, and a large amount of low-density cement slurry needs to be used in coalbed methane, shale oil, ultra-deep well and other engineering. In order to avoid the occurrence of low-pressure leakage in the process of deep oil and gas exploitation, the whole well cementing construction gradually becomes the mainstream, and the use of low-density cement slurry for long sealing section cementing construction of the upper layer is continuously expanding. In order to stabilize and improve the cementing quality, it is urgent to further improve the low-density cement slurry system, develop cement slurry materials with more stable performance and lower density and mixing process, so as to improve the cementing quality and solve the contradiction between the cost and performance of low-density cement slurry.

[0003] The commonly used low-density cement slurry system in the prior art is glass microbead system, floating bead system, fly ash system and perlite system, which is relatively mature. However, the traditional low-density cement slurry has high permeability, and is prone to oil and gas water channeling.

[0004] In recent years, nano material technology has been researched and applied. Nano silicon dioxide has super high specific surface area and good filling effect, which can improve the suspension stability of cement slurry. In addition, it can provide hydration sites as crystal nucleus and can be secondary hydrated with calcium hydroxide generated by cement hydration, so as to improve the mechanical properties and impermeability of cement stone. However, due to the small particle size, it is easy to cause agglomeration and is difficult to disperse. In recent years, some researches have turned to the research of nano silicon sol, but the research of nano silicon sol used in low-density cement slurry is not systematic. SUMMARY

[0005] In order to solve the problems in the prior art, the present application provides a low-density cement slurry, which uses oil well cement as cementing material, adds desert sand, rice husk ash and modified silicon sol, and uses high water-binder ratio to prepare low-density cement slurry with good stability and high mechanical properties without adding additional lightening agent, which can be used in medium-high temperature cementing engineering.

[0006] Specifically, the low-density cement slurry of the present application is characterized by being composed of the following raw materials in parts by weight: oil well cement 100-110 parts, desert sand 15-18 parts, rice husk ash 3-5 parts, modified silicon sol 3-4 parts, fluid loss reducer 3-4 parts, dispersant 2-3 parts, retarder 1-2 parts, defoamer 0.5-0.8 parts and water 90-100 parts.

[0007] In the prior art, in order to prepare a low-density cement slurry, a lightening agent such as microbeads, floating beads, perlite, etc. is often added, and the cement stone is prone to mechanical property attenuation in a high-temperature environment, and a raw material such as silica sand and microsilica powder is often added to resist the strength decay under high temperature. Desert sand is difficult to be directly used in construction engineering due to its fine particle size and round particles, and the present application uses desert sand to completely replace silica sand, and through a large number of experiments, part of rice husk ash and modified silica sol are added to improve the water-binder ratio, and a low-density cement slurry meeting the requirements of well cementing is prepared without adding a lightening agent such as microbeads.

[0008] Preferably, the preparation process of the modified silica sol is that the silica sol is uniformly mixed with a silane coupling agent, and then nano-microcrystalline cellulose is added and uniformly mixed.

[0009] The present application adds nano-microcrystalline cellulose to the silica sol modified by the silane coupling agent to prepare the modified silica sol, which has better compatibility with the cement base material compared with the silica sol, avoids the formation of an arc-shaped crack at the contact interface between the silica sol particles and the cement base, thereby improving the structural integrity of the cement stone, and the modified silica sol still maintains its suspension stability effect, still has the early strength enhancement characteristics of providing hydration sites and reacting with calcium hydroxide to generate a gel, the nano-microcrystalline cellulose and the hydrated gel are more closely interlaced, and the overall compressive strength of the cement stone is improved, in addition, the modified silica sol can be synergized with the rice husk ash to realize that the slurry after the introduction of desert sand meets the requirements of well cementing, and the low-density cement slurry can be prepared without adding a lightening agent again under the condition of a high water-binder ratio.

[0010] Preferably, the oil well cement is G-grade oil well cement.

[0011] Preferably, the particle size of the desert sand is ≤0.2 mm.

[0012] Preferably, the SiO2 content in the rice husk ash is ≥85%.

[0013] Preferably, the SiO2 content in the silica sol is 40-50%.

[0014] Preferably, the mass ratio of the silica sol, the silane coupling agent and the nano-microcrystalline cellulose is 1:(0.1-0.2):(0.2-0.3).

[0015] Preferably, the fluid loss additive is at least one of G33S, DRF-120L and BXF-200L.

[0016] Preferably, the dispersant is at least one of Weihui GD-1 and SXY.

[0017] Preferably, the retarder is at least one of tartaric acid, boric acid and organic phosphate.

[0018] The application also relates to a preparation method of the low-density cement slurry.

[0019] The application also relates to application of the low-density cement slurry in cementing engineering.

[0020] The application has the following technical advantages:

[0021] 1. The application adds desert sand to realize application of the desert sand in the cementing field,

[0022] 2. The application prepares modified silica sol, and has good stability and enhancement effects,

[0023] 3. The application uses desert sand, rice husk ash and modified silica sol, and can prepare the low-density cement slurry without adding silica sand, a weight reducer and silica powder by improving a water-binder ratio, the cement slurry has a density of 1.30-1.40 g / cm 3 , an API fluid loss is less than 50 mL, and can meet the use in a 120 DEG C medium-high temperature cementing engineering. DETAILED DESCRIPTION

[0024] To represent technical effects of the application, cement slurry is prepared and performances thereof are detected. In the test process, G-grade oil well cement is used as the cement, the particle size of the desert sand is less than or equal to 0.2 mm, the SiO2 content in the rice husk ash is 89%, the SiO2 mass content in the silica sol is 50%, G33S is used as the fluid loss reducer, GD-1 is used as the dispersant, and tartaric acid is used as the retarder.

[0025] Example 1

[0026] The cement slurry is composed of the following raw materials in parts by weight: oil well cement 107 parts, desert sand 16 parts, rice husk ash 5 parts, modified silica sol 3 parts, fluid loss reducer 4 parts, dispersant 2.5 parts, retarder 2 parts, defoaming agent 0.6 parts and water 100 parts, the preparation process of the modified silica sol is that silica sol is uniformly mixed with silane coupling agent, nano microcrystalline cellulose is added and uniformly mixed, and the modified silica sol is obtained, wherein the mass ratio of the silica sol, the silane coupling agent and the nano microcrystalline cellulose is 1:0.1:0.25.

[0027] It is detected that the cement slurry has a density of 1.34 g / cm 3 , an API fluid loss of 20 mL, no free liquid, a sedimentation stability of 0.01 g / cm 3 , and a cement stone compressive strength of 11.6 MPa at 30 DEG C for 24 hours.

[0028] Example 2

[0029] Cement slurry, which is composed of the following raw materials in parts by weight: oil well cement 105 parts, desert sand 17 parts, rice husk ash 4 parts, modified silica sol 4 parts, fluid loss additive 3.5 parts, dispersant 3 parts, retarder 2 parts, defoaming agent 0.6 parts, and water 100 parts, wherein the preparation process of the modified silica sol is as follows: uniformly mix silica sol and silane coupling agent, add nano microcrystalline cellulose, and uniformly mix, to obtain the modified silica sol, wherein the mass ratio of silica sol, silane coupling agent, and nano microcrystalline cellulose is 1:0.2:0.3.

[0030] It is detected that the density of the cement slurry is 1.36 g / cm 3 , API fluid loss is 10 mL, free fluid is 0, and sedimentation stability is 0.01 g / cm 3 , and the 24 h cement stone compressive strength at 30℃ is 12.2 MPa.

[0031] Comparative Example 1

[0032] Cement slurry, which is composed of the following raw materials in parts by weight: oil well cement 105 parts, desert sand 17 parts, rice husk ash 4 parts, modified silica sol 4 parts, fluid loss additive 3.5 parts, dispersant 3 parts, retarder 2 parts, defoaming agent 0.6 parts, and water 100 parts, wherein the preparation process of the modified silica sol is as follows: uniformly mix silica sol and silane coupling agent, add nano microcrystalline cellulose, and uniformly mix, to obtain the modified silica sol, wherein the mass ratio of silica sol, silane coupling agent, and nano microcrystalline cellulose is 1:0.2:0.3.

[0033] It is detected that the density of the cement slurry is 1.56 g / cm 3 , API fluid loss is 40 mL, free fluid is 7 mL, and sedimentation stability is 0.04 g / cm 3 , and the 24 h cement stone compressive strength at 30℃ is 9.6 MPa.

[0034] Comparative Example 2

[0035] Cement slurry, which is composed of the following raw materials in parts by weight: oil well cement 105 parts, desert sand 17 parts, rice husk ash 4 parts, modified silica sol 4 parts, fluid loss additive 3.5 parts, dispersant 3 parts, retarder 2 parts, defoaming agent 0.6 parts, and water 100 parts, wherein the preparation process of the modified silica sol is as follows: uniformly mix silica sol and silane coupling agent, add nano microcrystalline cellulose, and uniformly mix, to obtain the modified silica sol, wherein the mass ratio of silica sol, silane coupling agent, and nano microcrystalline cellulose is 1:0.2:0.3.

[0036] It is detected that the density of the cement slurry is 1.49 g / cm 3 , API fluid loss is 30 mL, free fluid is 3 mL, and sedimentation stability is 0.03 g / cm 3 , and the 24 h cement stone compressive strength at 30℃ is 10.1 MPa.

[0037] Comparative Example 3

[0038] Cement slurry, consisting of the following raw materials by weight: oil well cement 105 parts, desert sand 17 parts, rice husk ash 4 parts, silica sol 4 parts, fluid loss additive 3.5 parts, dispersant 3 parts, retarder 2 parts, defoamer 0.6 parts, water 100 parts.

[0039] The cement slurry density is 1.63 g / cm 3 , API fluid loss is 60 mL, free fluid is 10 mL, and sedimentation stability is 0.15 g / cm 3 , and the 30℃, 24h cement stone compressive strength is 8.0 MPa.

[0040] Comparative Example 4

[0041] Cement slurry, consisting of the following raw materials by weight: oil well cement 105 parts, desert sand 17 parts, rice husk ash 4 parts, floating bead 4 parts, fluid loss additive 3.5 parts, dispersant 3 parts, retarder 2 parts, defoamer 0.6 parts, water 100 parts.

[0042] The cement slurry density is 1.88 g / cm 3 , API fluid loss is 80 mL, free fluid is 30 mL, and sedimentation stability is 0.38 g / cm 3 , and the 30℃, 24h cement stone compressive strength is 6.3 MPa.

[0043] Comparative Example 5

[0044] Cement slurry, consisting of the following raw materials by weight: oil well cement 105 parts, desert sand 17 parts, rice husk ash 4 parts, silica sol 4 parts, fluid loss additive 3.5 parts, dispersant 3 parts, retarder 2 parts, defoamer 0.6 parts, water 60 parts.

[0045] The cement slurry density is 1.90 g / cm 3 , API fluid loss is 20 mL, free fluid is 0, and sedimentation stability is 0.03 g / cm 3 , and the 30℃, 24h cement stone compressive strength is 9.8 MPa.

[0046] As can be seen from the examples and comparative examples, both Example 1 and Example 2 use desert sand, rice husk ash, and modified silica sol in combination with oil well cement as the base material, and are supplemented with functional additives and high water-binder ratio. The results show that this system successfully achieves low density, extremely low API fluid loss, excellent slurry stability, and good early compressive strength without relying on traditional lightening agents (such as floating beads), fully meeting the requirements of medium-high temperature well cementing engineering.

[0047] The test results of Comparative Example 1 show that the density of the cement slurry is significantly increased, and the performances of the cement slurry are all declined, by replacing the core components of desert sand and rice husk ash with traditional silica sand and fly ash; the performances of the cement slurry are all declined by using silicon powder to replace rice husk ash in Comparative Example 2, which shows that although the main component of silicon powder is silicon dioxide, the use effect of silicon powder is not as good as that of rice husk ash; the performance of the cement slurry is declined by directly using unmodified silicon sol in Comparative Example 3 relative to Example 2; the performance of the cement slurry is seriously deteriorated by using traditional lightening agent of floating beads to replace modified silicon sol in Comparative Example 4, which shows that simply relying on lightening agent cannot be applied to the cement slurry system of desert sand; the density is increased, and the other performances are also decreased relative to Example 2 by reducing the water-binder ratio while using unmodified silicon sol in Comparative Example 5.

[0048] In summary, the core invention point of the present application is that the desert sand, rice husk ash and modified silicon sol are synergistically used, the desert sand is used to replace raw materials such as silica sand and micro-silicon powder, the high-value reuse of the desert sand is realized, the rice husk ash and the modified silicon sol are innovatively used for synergistic modification in order to cooperate with the use of the desert sand, and the water-binder ratio is increased, so that the low-density cement slurry with good stability and high mechanical properties is prepared without using additional lightening agent, the problem of mechanical property attenuation of the cement slurry at high temperature is overcome, and the cement slurry can be used for high-temperature well cementing engineering.

[0049] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A low-density cement slurry, characterized in that, It is composed of the following raw materials in parts by weight: 100-110 parts oil well cement, 15-18 parts desert sand, 3-5 parts rice husk ash, 3-4 parts modified silica sol, 3-4 parts water loss reducer, 2-3 parts dispersant, 1-2 parts retarder, 0.5-0.8 parts defoamer, and 90-100 parts water. The modified silica sol is prepared by: mixing silica sol and silane coupling agent evenly, adding nanocrystalline cellulose, and mixing evenly to obtain the final product. The mass ratio of silica sol, silane coupling agent, and nanocrystalline cellulose is 1:(0.1-0.2):(0.2-0.3).

2. The low-density cement slurry according to claim 1, characterized in that, The oil well cement is Grade G oil well cement.

3. The low-density cement slurry according to claim 1, characterized in that, The desert sand has a particle size of ≤0.2mm.

4. The low-density cement slurry according to claim 1, characterized in that, The SiO2 content in the rice husk ash is ≥85%.

5. The low-density cement slurry according to claim 1, characterized in that, The silica sol contains 40-50% SiO2 by mass.

6. The low-density cement slurry according to claim 1, characterized in that, The water loss reducing agent is at least one of G33S, DRF-120L, and BXF-200L.

7. The low-density cement slurry according to claim 1, characterized in that, The dispersant is at least one of Weihui GD-1 and SXY.

8. The method for preparing low-density cement slurry according to any one of claims 1-7, characterized in that, The process includes the following steps: mixing all the raw materials evenly to obtain the final product.

9. The application of the low-density cement slurry according to any one of claims 1-7 in cementing engineering.