Abstract

Oil well cement has brittleness, insufficient elastic deformation ability, and poor resistance to external loads, which hinders the development of oil and gas well cementing technology. In order to overcome these shortcomings, an anionic styrene butadiene latex powder elastic material was synthesized. Anionic styrene butadiene latex powder (SBRM) was obtained by using polybutadiene (PB) and styrene (St) as raw materials, maleic acid (MA) as modified monomer, m (PB): m (St): m (MA)=6:2:1, and reacting at 70℃ for 7 hours. After drying and grinding, anionic styrene butadiene latex powder (SBRM) was obtained. The structure and performance of SBRM were characterized by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, thermogravimetric analysis, water wettability testing, and microscopy. The synthesized product was confirmed to be SBRM by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy analysis; According to thermogravimetric analysis, the synthesized SBRM has good thermal stability. The main chain of SBRM only decomposes when the temperature is above 375℃; The contact angle of SBRM is 47.1°; According to formula 1 {G grade oil well cement+2% fluid loss additive (SWJ-1)+1% dispersant (SXY), the water cement ratio of the cement slurry is 0.44, all of which are mass ratios.} blank group cement slurry is prepared. According to formula 2 {G grade oil well cement+2% fluid loss additive (SWJ-1)+1% dispersant (SXY)+3%/5%/7% SBRM, the water cement ratio of the cement slurry is 0.44} to prepare styrene butadiene latex powder cement slurry. According to the formula 3 {G grade oil well cement+2% fluid loss additive (SWJ-1)+1% dispersant (SXY)+3%/5%/7% commercially available styrene butadiene latex (XSBR), a water cement ratio of 0.44} to prepare a commercially available anionic styrene butadiene latex cement slurry and conduct cement slurry performance testing. Then, the performance of cement paste was tested by curing at 90℃ for 48 hours. The results show that SBRM can be well dispersed in cement, while improving the fluidity of cement slurry and significantly improving the elasticity of cement paste. The elastic modulus of cement paste with styrene butadiene latex powder is reduced by 39.8% compared to blank cement paste, and the elastic modulus is reduced by 28.3% compared to cement paste with commercially available styrene butadiene latex powder. Microscopic morphology analysis shows that SBRM filling in the internal pores of cement stone can improve the compactness of cement stone, alleviate external impact capacity, and thus improve the elasticity of cement stone.

Portland cement is a material with inherent brittleness, which has good construction and material properties and is commonly used for oil and gas well cementing. However, during the process of oil and gas well extraction, brittle cement stones are prone to microcracks and even breakage due to the influence of subsequent cementing construction and complex forces in underground rock formations, which is not conducive to subsequent oil and gas extraction and production increase. At the same time, oil and gas wells will undergo multiple injection and extraction, while underground gas storage tanks will undergo multiple injection and extraction. Therefore, cement slurry needs to have good deformation ability to cushion stress after solidification underground. If the deformation capacity is insufficient, it will lead to the failure of interlayer sealing in oil and gas wells, thereby affecting the use of oil and gas wells. After solidification, Portland cement may exhibit some pores and microcracks. With the action of stress, the microcracks in the cement paste will further expand, forming larger cracks, which can easily weaken the interlayer sealing ability of the cement sheath and bring certain difficulties to subsequent development.

In engineering, elastic materials are usually added to alleviate the problems of microcracks and failure of cement ring sealing integrity in cement stone. Currently, the most commonly used elastic materials are rubber powder and latex. Rubber powder is usually an inert material with hydrophobic surface, and has poor compatibility with cement slurry. At the same time, when the dosage is large, the cement slurry will settle. Therefore, the use of rubber powder in cement is limited. Liquid latex is widely used in oil well cement, but it has poor storage stability, weak temperature resistance, and problems such as easy demulsification and foaming during slurry mixing. It is necessary to improve the performance of liquid latex and solidify it for powder production. Styrene butadiene latex powder can effectively avoid problems such as demulsification and foaming during the use of liquid latex, greatly improving the transportation and storage convenience, thereby expanding the application prospects of styrene butadiene latex.

Therefore, studying a styrene butadiene latex powder that can improve the brittleness of cement paste is of great significance. This article uses polybutadiene (PB) and styrene (St) as raw materials, maleic acid (MA) as modified monomer, m (PB): m (St): m (MA)=6:2:1, and reacts at 70℃ for 7 hours. After drying and grinding, anionic styrene butadiene latex powder (SBRM) is obtained. The structure and performance of SBRM were characterized by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, thermogravimetric analysis, water wettability testing, and microscopy. SBRM, as a key material for improving the elastic properties of oil well cement, can alleviate the problem of high brittleness of cementing cement.

1. Experimental Part

1.1 Instruments and Reagents

* WQF520 infrared spectrometer (KBr tablet);

* Bruker III HD 400 nuclear magnetic resonance spectrometer;

* DSC823 TGA/SD-TA85/e thermogravimetric analyzer;

* KRUSS DSA30S interface parameter integrated measurement system;

* AMG EVOSFL type eyeless inverted fluorescence digital microscope;

* NYL-300 pressure testing machine;

* RTR-1500 triaxial rock mechanics tester;

* Phenmo Pro X-type desktop scanning electron microscope.

*  Styrene (St), sodium dodecyl sulfate (SDS), ammonium persulfate (APS), sodium hydroxide (NaOH), and maleic acid (MA) are all analytical pure and purchased from Chengdu Kelong Chemical Reagent Factory;

*  Polybutadiene (PB), industrial grade, purchased from Beijing Yanshan Petrochemical Co., Ltd;

* Commercially available styrene butadiene latex (XSBR), industrial grade, purchased from Foshan Jinjia New Material Technology Co., Ltd;

*  G grade oil well cement, purchased from Jiahua Special Cement Co., Ltd;

*  The fluid loss additive (SWJ-1), dispersant (SXY), and defoamer (X60L) are provided by the drilling company of Shengli Oilfield;

*  Deionized water and tap water are self-made in the laboratory.

1.2 Synthesis

Styrene butadiene latex powder (SBRM) was synthesized by lotion polymerization. Weigh 48.0g St and 16.0g PB and place them in a beaker. Dissolve 2.4g SDS in 50.0g deionized water and add them to the aforementioned beaker. Use an emulsifying machine at 6000r/min to emulsify and disperse for 2 minutes, and then transfer them to a three necked flask to heat up to 70℃. Take 1.2g of APS initiator, dissolve it in 50.0g of deionized water, and drop it into a three necked flask. Dissolve 8.0g of MA in 50.0g of deionized water, adjust pH=8 with a 30% NaOH solution, and add it dropwise to a three necked flask. Then, react at 70℃ for 7 hours to obtain a milky white liquid product SBRM. Then, dry it in an oven and grind it to obtain a solid SBRM. The reaction process is shown in Figure 1.

1.3 Characterization and Performance Testing

(1) Characterization of Styrene Butadiene Latex Samples

Use an infrared spectrometer to test the absorption peak of SBRM in the wavelength range of 4000~400cm^-1; Use nuclear magnetic resonance spectroscopy to make the structural characterization of SBRM; The thermal stability performance of SBRM was tested using a thermogravimetric analyzer, with a heating rate of 20 ℃/min and a testing temperature of 0-800℃; Using a contact angle measuring instrument to test the water wettability of SBRM; The water dispersibility of SBRM was observed using a fluorescence digital microscope.

(2)  Cement Slurry Performance Testing

Referring to GB/T 8077-2012 Test Method for Uniformity of Concrete Admixtures and GB/T 19139-2012 Test Method for Oil Well Cement, according to formula 1 {G grade oil well cement+2% fluid loss additive (SWJ-1)+1% dispersant (SXY), the water cement ratio of the cement slurry is 0.44, all of which are mass ratios.} blank group cement slurry is prepared. According to formula 2 {G grade oil well cement+2% fluid loss additive (SWJ-1)+1% dispersant (SXY)+3%/5%/7% SBRM, the water cement ratio of the cement slurry is 0.44} to prepare styrene butadiene latex powder cement slurry. According to the formula 3 {G grade oil well cement+2% fluid loss additive (SWJ-1)+1% dispersant (SXY)+3%/5%/7% commercially available styrene butadiene latex (XSBR), a water cement ratio of 0.44} to prepare a commercially available anionic styrene butadiene latex cement slurry. And the flowability and thickening performance of SBRM were tested at 90℃.

(3) Performance Testing of Cement Stone

According to the GB/T 19139-2012 Oil Well Cement Test Method, prepare cement slurry according to the three formulas in the cement slurry performance test. Test the compressive strength and elastic modulus after curing at 90℃ for 48 hours.