High-toughness high-temperature oil well cement

Abstract

The invention discloses high-toughness high-temperature well cementation cement, and relates to the technical field of oil and gas well cementation materials. The high-toughness high-temperature well cementing cement provided by the invention is prepared from the following components in parts by weight: 20 to 35 parts of tricalcium silicate, 40 to 55 parts of dicalcium silicate, 14 to 20 parts of tetra calcium aluminoferrite, 0.5 to 2 parts of tricalcium aluminate, 3 to 10 parts of calcium zirconate and 2 to 4 parts of gypsum. The high-temperature well cementation cement mainly solves the problems of poor toughness and unstable compressive strength of the high-temperature well cementation cement for deep and ultra-deep well cementation, and achieves the purpose of improving the toughness and strength stability of set cement by changing the mineral components of the cement.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas well cementing materials, and more particularly to a high-toughness, high-temperature oil well cement. Background Art

[0002] The development of deep and ultra-deep oil and gas resources faces numerous challenges. As well depth increases, bottomhole temperatures and pressures continue to rise, and well conditions become more complex. Current exploration and development processes, equipment, and materials cannot fully meet these requirements. Cementing cement, under conditions of high temperature and pressure, suffers from poor compressive strength stability, low strength values, and high brittleness. Under the stresses of the formation, wellbore, and temperature fluctuations, the cement sheath is prone to deformation and cracking. The complex operating conditions within deep and ultra-deep oil and gas wells place even higher demands on the cement sheath's mechanical properties, such as compressive strength and toughness.

[0003] Currently, there are three main methods for improving the toughness of cement. One method involves adding organic elastic materials to cement to improve its elastic toughness. For example, the invention patent application with publication number CN109609107A discloses a high-temperature-resistant and tough material and its preparation method. The main components of the high-temperature-resistant and tough material are: 10-20 parts latex powder; 10-40 parts modified rubber powder; 20-50 parts polyimide resin; 5-10 parts aminosilane coupling agent; and 15-60 parts modified nanotubes. Another example is the invention patent application with publication number CN114350334A, which discloses a high-temperature-resistant and tough cementing slurry system in which the high-temperature toughening material is polyetheretherketone resin.

[0004] The second is to add fiber materials to improve the toughness of cement paste through fiber toughening. For example, the invention patent application with application publication number CN113402186A discloses a method for preparing a cement slurry toughening agent, cement slurry, and its preparation method. The method mainly involves modifying carbon fibers and nanoparticles separately, causing the surface-modified nanoparticles and surface-modified carbon fibers to react, and then chemically bonding them to obtain a cement slurry toughening agent, thereby improving the stability of the cement slurry toughening agent under high temperature conditions. Another example is the invention patent application with application publication number CN112341067A, which discloses an ultra-high temperature, high-strength and tough cement slurry system in which the ultra-high temperature toughening material is halloysite nanotubes.

[0005] The third method is to add inorganic toughening particles to cement to improve the toughness of the cement paste through particle toughening. For example, CN116639894A discloses a high-temperature and high-pressure resistant toughened shale gas cement and its preparation method, which improves the toughness of the cement paste by increasing the ferroaluminate mineral phase in the cement.

[0006] The above three toughening methods can effectively improve the toughness of cementing cement. However, in deep and ultra-deep oil and gas well cementing projects, the toughening effect of these three types of toughening methods is weakened under high temperature and high pressure conditions, and at the same time, it will affect the high-temperature strength of cement. Summary of the Invention

[0007] In order to overcome the defects and shortcomings of the above-mentioned prior art, the present invention provides a high-toughness, high-temperature oil well cement. The present invention introduces phase change toughening particles to improve the toughness of cement stone under high temperature conditions, avoid brittle failure of cement stone under external stress, and at the same time improve the high-temperature strength stability of cement stone, ensure the integrity of the cement ring structure, and achieve long-term sealing performance of high-temperature and high-pressure cement stone rings in ultra-deep wells.

[0008] The present invention provides a high-toughness, high-temperature oil well cement. The high-toughness, high-temperature oil well cement comprises cement clinker and gypsum. The mineral composition of the cement clinker, in parts by weight, comprises the following mineral composition: 20-35 parts of tricalcium silicate; 40-55 parts of dicalcium silicate; 14-20 parts of tetracalcium aluminoferrite; Tricalcium aluminate 0.5-2 parts; 3-10 parts of calcium zirconate; The calcium zirconate is obtained by reacting zirconium raw materials with calcium oxide during the high-temperature calcination of cement clinker, and is distributed in tetracalcium aluminoferrite with a particle size of 0.2-1 μm. The amount of gypsum in the high-toughness and high-temperature oil well cement is 2-4 parts by weight.

[0009] Further preferably, the cement clinker is obtained by mixing cement raw material powder and calcining the cement raw material, and the cement raw material comprises the following components by weight percentage: Limey raw materials: 65-75%; Clay raw materials: 9-23%; Iron raw materials: 2-6%; Zirconium raw materials 2-10%.

[0010] More preferably, the calcareous raw material is any one or a combination of two of limestone, carbide slag, white mud and high-magnesium ashstone; the clay raw material is any one or a combination of two of red sand, quartz sand, clay, shale and kaolin; and the iron raw material is sulfuric acid slag, lead-zinc slag or copper slag.

[0011] More preferably, the zirconium raw material is zirconium silicate, zircon or zirconium oxide.

[0012] More preferably, the zirconium oxide content in the zirconium raw material is not less than 30%.

[0013] More preferably, the cement raw material calcination temperature is between 1300°C and 1450°C.

[0014] More preferably, the high-toughness and high-temperature oil well cement is prepared by mixing cement clinker and gypsum and then ball milling.

[0015] More preferably, the specific surface area of ​​the high-toughness, high-temperature oil well cement is 280-350 g / cm 3 .

[0016] More preferably, the gypsum is anhydrite or dihydrate gypsum.

[0017] Compared with the prior art, the beneficial technical effects brought about by the technical solution of the present invention are as follows: 1. Excellent High-Toughness Toughening: The high-toughness, high-temperature oil well cement of this invention incorporates zirconium as a raw material. Zirconium oxide in the raw material reacts with calcium oxide at the calcination temperature to form calcium zirconate, which is evenly distributed in the cement's tetracalcium aluminoferrite in the form of fine particles. Under high-temperature hydrothermal conditions, calcium zirconate reacts with water to form calcium hydroxide and zirconium oxide. The calcium hydroxide further reacts with silicon dioxide to form calcium silicate hydration products, with zirconium oxide present in these hydration products. During the formation and growth of zirconium oxide crystals, the presence of a large amount of calcium oxide ions in the solution ultimately leads to the formation of tetragonal zirconium oxide (t-ZrO2). When the cement paste is subjected to external stress, the tetragonal zirconium oxide (t-ZrO2) transforms to the monoclinic phase (m-ZrO2). This phase transformation is accompanied by shear strain and volume change, effectively absorbing the damaging energy, reducing stress concentration at the crack tip, and inhibiting crack propagation, ultimately achieving phase transformation toughening. Compared with other toughening methods, phase change toughening does not affect the working performance of high-temperature cementing cement, is not affected by temperature, and also has good toughening effect under high temperature conditions.

[0018] 2. Strong bonding between phase-change toughening particles and hydration products: The phase-change process of zirconia under stress requires that external stress be smoothly transferred to the zirconia particles, which places high demands on the interfacial bonding between the cement hydration products and zirconia. Compared to directly adding zirconia to cement, in-situ generated zirconia particles are more evenly distributed and more tightly bonded to the cement hydration products. External forces acting on the cement paste can be effectively transferred to the zirconia particles, effectively achieving the phase-change toughening effect of ZrO2.

[0019] 3. Good high-temperature strength stability: High-temperature strength stability is one of the challenges facing high-temperature cement. When the curing temperature exceeds 230°C, the hydration products of high-temperature cement are mainly xonotlite. As the xonotlite crystals grow and coarsen, the internal porosity increases, resulting in a significant decrease in the strength of the cement paste. The zirconium oxide particles formed in the hydration products of high-toughness high-temperature oil well cement can effectively exert a steric hindrance effect, preventing the growth and coarsening of xonotlite crystals in the direction of the preferred growth phase. This steric hindrance effect achieves xonotlite grain refinement and prevents the increase of internal porosity in the cement paste, thereby achieving the goal of improving the high-temperature strength stability of the cement paste. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD diffraction pattern of the high-toughness and high-temperature oil well cement clinker according to Example 1 of the present invention.

[0021] Figure 2 This is a petrographic SEM image of the high-toughness, high-temperature oil well cement clinker according to Example 1 of the present invention.

[0022] Figure 3 This is an EDS scan of the high-toughness, high-temperature oil well cement clinker according to Example 1 of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Example 1 As a preferred embodiment of the present invention, this embodiment provides a high-toughness, high-temperature oil well cement comprising, by weight, 20 parts tricalcium silicate, 55 parts dicalcium silicate, 15 parts tricalcium aluminoferrite, 0.5 parts tricalcium aluminate, 7.5 parts calcium zirconate, and 2 parts gypsum. The calcium zirconate is obtained by reacting zirconium with calcium oxide during the high-temperature calcination of cement clinker and is distributed in tetracalcium aluminoferrite, with a particle size of 0.2-1 μm.

[0025] The raw material components of the high-toughness, high-temperature oil well cement in this embodiment are: carbide slag: 65%; red sand: 22%; lead-zinc slag: 6%; and zircon: 7%. The zircon contains 56% zirconium oxide. The gypsum is anhydrite. The raw material calcination temperature of the cement is 1350°C, and the specific surface area of ​​the cement after grinding is 280g / cm. 3 .

[0026] Example 2 As another preferred embodiment of the present invention, this embodiment provides a high-toughness, high-temperature oil well cement comprising, by weight, 35 parts tricalcium silicate, 40 parts dicalcium silicate, 16 parts tricalcium aluminoferrite, 1 part tricalcium aluminate, 6 parts calcium zirconate, and 2 parts gypsum. The calcium zirconate is obtained by reacting zirconium with calcium oxide during the high-temperature calcination of cement clinker and is distributed in tetracalcium aluminoferrite, with a particle size of 0.2-1 μm.

[0027] The raw material components of the high-toughness, high-temperature oil well cement in this embodiment are: white mud 70%; clay 6%; quartz sand 17%; sulfate slag 3%; and zircon 4%. The zircon contains 56% zirconium oxide. The gypsum is dihydrate gypsum. The raw material is calcined at 1400°C, and the specific surface area of ​​the cement after grinding is 300 g / cm. 3 .

[0028] Example 3 As another preferred embodiment of the present invention, this embodiment provides a high-toughness, high-temperature oil well cement comprising, by weight, 31 parts tricalcium silicate, 47 parts dicalcium silicate, 14 parts tricalcium aluminoferrite, 2 parts tricalcium aluminate, 3 parts calcium zirconate, and 3 parts gypsum. The calcium zirconate is obtained by reacting a zirconium raw material with calcium oxide during the high-temperature calcination of cement clinker. The calcium zirconate is distributed in tetracalcium aluminoferrite and has a particle size of 0.5-1 μm.

[0029] The raw material composition of the high-toughness, high-temperature oil well cement in this embodiment is: high-magnesium wollastonite: 8%, limestone: 67%; clay: 8%; shale: 13%; copper slag: 2%; zirconium oxide: 2%. The zirconium oxide has a purity of 99.5%. The gypsum is dihydrate gypsum. The raw material is calcined at 1450°C, and the specific surface area of ​​the cement after grinding is 350g / cm. 3 .

[0030] Example 4 As another preferred embodiment of the present invention, this embodiment provides a high-toughness, high-temperature oil well cement comprising, by weight, 23 parts tricalcium silicate, 41 parts dicalcium silicate, 20 parts tricalcium aluminoferrite, 2 parts tricalcium aluminate, 10 parts calcium zirconate, and 4 parts gypsum. The calcium zirconate is obtained by reacting a zirconium raw material with calcium oxide during the high-temperature calcination of cement clinker. The calcium zirconate is distributed in tetracalcium aluminoferrite and has a particle size of 0.2-1 μm.

[0031] The raw material components of the high-toughness, high-temperature oil well cement in this embodiment are: limestone: 75%; quartz sand: 6%; kaolin: 3%; sulfate slag: 6%; zirconium silicate: 10%. The zirconium silicate contains 56% zirconium oxide. The gypsum is dihydrate gypsum. The raw material calcination temperature is 1300°C, and the specific surface area of ​​the cement after grinding is 350g / cm. 3 .

[0032] Comparative Example 1 The cement in this comparative example is 100 parts of Class D high-resistance oil well cement. In this comparative example, Class D high-resistance oil well cement gradually meets the relevant requirements of GB / T10238-2015.

[0033] Comparative Example 2 The cement in this comparative example uses 99.7 parts of Class D high-resistance oil well cement and 0.3 parts of chopped carbon fiber. In this comparative example, the Class D high-resistance oil well cement meets the relevant requirements of GB / T 10238-2015, and the length of the chopped carbon fiber is 3-6 mm.

[0034] Test example Based on the cement prepared in Examples 1-4 and Comparative Examples 1-2, quartz sand was added. The quartz sand had a SiO2 content of 97.8% and a fineness of 350 mesh. The specific cement slurry formula is shown in Table 1 below. Cement slurries were then prepared according to the method specified in GB / T19139 for the preparation of elastic modulus and compressive strength samples.

[0035] (1) Elastic modulus test The cement slurry was poured into a test mold for the elastic modulus of cement stone to form a cylinder with a height of 50 mm and a diameter of 25 mm. The mold was placed in a pressurized curing kettle at 250°C and cured for 7 days. After the curing was completed, the elastic modulus of the sample was tested on a triaxial testing machine. The test results are shown in Table 1.

[0036] (2) Compressive strength test The cement slurry was poured into a test mold for the compressive strength of cement paste. The test mold was a cube with a side length of 50 mm (or 2 in). After the mold was filled and covered with a cover plate, it was placed in a pressurized curing kettle at 250°C for curing for 7 and 14 days. After curing, the compressive strength of the cement paste was tested on a pressure testing machine. The test results are shown in Table 1.

[0037] Table 1 is the cement slurry ratio, compressive strength and elastic modulus data of Examples 1-4 and Comparative Examples 1-2 The data in Table 1 show that the cement slurries prepared in Examples 1-4 and Comparative Examples 1-2 were both cured at 250°C. Comparative Examples 1-2 are based on Grade D oil well cement, a type of cement used for high-temperature cementing. Even after curing at 250°C, Grade D oil well cement still exhibits low strength and a decline in 14-day compressive strength. Under identical mix proportions and testing conditions, the cement slurries prepared in Examples 1-4 and Comparative Examples 1-2 exhibit significantly better compressive strength than the cement slurries in Comparative Examples 1-2 after curing at 250°C, and the 14-day compressive strength shows no significant decline compared to the 7-day compressive strength.

[0038] Furthermore, in Comparative Example 2, chopped carbon fibers were added to the Class D oil well cement to improve the toughness of the cement paste. Compared to Comparative Example 1, the elastic modulus of the cement paste was significantly reduced, achieving some improvement in toughness, but the elastic modulus was still significantly higher than that of Examples 1-4. High-toughness, high-temperature oil well cement contains calcium zirconate, and the zirconium oxide formed after high-temperature hydration can act as a phase-transformation toughening agent, effectively reducing the elastic modulus of the cement paste and achieving the goal of improving its toughness. This toughening effect is significantly superior to that of fiber-based toughening.

[0039] Figure 1 This is the XRD diffraction pattern of the high-toughness, high-temperature oil well cement clinker of Example 1. Analysis using the XRD pattern analysis software EVA shows that the cement clinker mainly contains C3S (tricalcium silicate), C2S (dicalcium silicate), C3A (tricalcium aluminate), C4AF (tetracalcium aluminoferrite) and CaZrO3 (calcium zirconate), indicating that through the high-temperature calcination process, the zirconium silicate in the cement raw material has completely reacted with calcium oxide to form calcium zirconate minerals. Figure 2 This is an SEM image of the petrographic phase of the high-toughness, high-temperature oil well cement clinker from Example 1. The gray area in the image represents tricalcium silicate and dicalcium silicate. The interstices between the tricalcium silicate and dicalcium silicate minerals should be tetracalcium aluminoferrite. The image shows the presence of numerous white particles with a particle size range of 0.2-1 μm in the interstices between the tricalcium silicate and dicalcium silicate minerals. Figure 3 This is the EDS scanning result of the white particles in the petrographic SEM image of the high-toughness and high-temperature oil well cement clinker in Example 1. The spectrum analysis results show that the white particle area contains a large amount of zirconium oxide in addition to common cement components such as calcium oxide, iron oxide, and aluminum oxide. It can be seen that Figure 2 The white particles are calcium zirconate.

[0040] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are intended to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or refinements made to the main design concept and spirit of the present invention that have no substantive significance, provided that the technical problems they solve are still consistent with those of the present invention, should be included in the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields should also be included in the patent protection scope of the present invention.

Claims

1. A high-toughness, high-temperature oil well cement, comprising cement clinker and gypsum, characterized in that: The mineral composition of the cement clinker, in parts by weight, includes the following mineral compositions: 20-35 parts of tricalcium silicate; 40-55 parts of dicalcium silicate; 14-20 parts of tetracalcium aluminoferrite; Tricalcium aluminate 0.5-2 parts; 3-10 parts of calcium zirconate; The calcium zirconate is obtained by reacting zirconium raw materials with calcium oxide during the high-temperature calcination of cement clinker, and is distributed in tetracalcium aluminoferrite with a particle size of 0.2-1 μm. The amount of gypsum in the high-toughness and high-temperature oil well cement is 2-4 parts by weight.

2. The high-toughness, high-temperature oil well cement according to claim 1, characterized in that: The cement clinker is obtained by mixing cement raw material powder and calcining. The cement raw material includes the following components by weight percentage: Limey raw materials: 65-75%; Clay raw materials: 9-23%; Iron raw materials: 2-6%; Zirconium raw materials 2-10%.

3. The high-toughness, high-temperature oil well cement according to claim 2, characterized in that: The calcareous raw material is any one or a combination of two of limestone, carbide slag, white mud and high-magnesium ashstone; the clay raw material is any one or a combination of two of red sand, quartz sand, clay, shale and kaolin; the iron raw material is sulfuric acid slag, lead-zinc slag or copper slag.

4. The high-toughness, high-temperature oil well cement according to claim 2, characterized in that: The zirconium raw material is zirconium silicate, zircon or zirconium oxide.

5. The high-toughness, high-temperature oil well cement according to any one of claims 2 to 4, characterized in that: The zirconium oxide content in the zirconium raw material is not less than 30%.

6. The high-toughness, high-temperature oil well cement according to any one of claims 2 to 4, characterized in that: The cement raw material calcining temperature is 1300°C-1450°C.

7. The high-toughness, high-temperature oil well cement according to any one of claims 1 to 4, characterized in that: The high-toughness and high-temperature oil well cement is prepared by mixing cement clinker and gypsum and then ball milling.

8. The high-toughness, high-temperature oil well cement according to claim 7, characterized in that: The specific surface area of ​​the high-toughness, high-temperature oil well cement is 280-350 g / cm 3 .

9. The high-toughness, high-temperature oil well cement according to any one of claims 1 to 4, characterized in that: The gypsum is anhydrite or dihydrate gypsum.

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