| With the exploration and development of petroleum and natural gas gradually developing towards deep and ultra-deep wells,higher requirements are put forward for cementing technology and cementing quality.In oil and gas well cementing engineering,cement slurry between casing and borehole wall solidifies to cement stone,which provides support and protection for casing,and plays an interlayer sealing role together with casing,which plays an important role in the follow-up work of cementing.However,due to the complex underground environment of deep and ultra-deep wells,and this complex environment will cause certain damage to the ordinary cementing cement stone,which makes the cement stone easy to break and fracture in subsequent perforation,fracturing and mining operations,and this will cause the failure of interlayer sealing,bury a major hidden danger for the follow-up mining work,and seriously affect the service life of oil wells.In order to improve the toughness of cement sheath and the mechanical properties of cement paste,a new inorganic material,CaSO4 whisker,is used as reinforcement material for cement paste.Firstly,the optimum conditions of whisker synthesis are determined through design experiments.The optimum reaction conditions are as followed:C(CaO)=C(H2SO4)=0.4 mol/L,reaction time is 10 h,reaction temperature is 90?.The CaSO4 whiskers prepared under these conditions have the characteristics of high aspect ratio structure,different aspect ratio and disorder.The mechanism and shortcomings of whiskers in cement paste are analyzed by SEM diagrams,and the modification direction of CaSO4 whiskers is determined according to the mechanism.In this paper,the surface of calcium sulfate whiskers is modified by tetraethyl orthosilicate(TEOS).The structure of the modified calcium sulfate whiskers are characterized by FT-IR,XRD and SEM.The results are as followed:FTIR spectra show that there are characteristic peaks of SiO2 at 1079 cm-1,976 cm-1 and 805 cm-1,indicating the presence of Si-O-Si in the modified whiskers.The SEM micrograph shows that there is obvious material adhesion on the surface of calcium sulfate whisker,while EDS element analysis shows that there is Si element in the layer on the surface of calcium sulfate whisker,and XRD spectrum shows that nano-SiO2 adhering to the surface of the whisker is amorphous.The application performance of the modified CaSO4 whisker in cement slurry is tested.The results show that when the addition of the modified whisker is 5%,the fluidity of the cement slurry is 23.5 cm,the water loss is 40 ml and the water precipitation is 0.8 ml.The thickening curve of the modified whisker cement slurry is stable at 90? and 120?,and there are no abnormal phenomena such as bulging,which indicates that the comprehensive performance of the modified whisker cement slurry is good.When the dosage of modified whisker is 5%,the compressive strength and flexural strength of modified whisker cement paste are 26 MPa and 7.2 MPa respectively after 24 hours curing,which are 52.9%and 67.4%higher than that of blank cement paste,while the compressive and flexural strength of unmodified whisker cement paste are 22 MPa and 6.3 MPa respectively,which are 29.4%and 46.5%higher than that of blank cement paste.The strength test and triaxial mechanical test results of cement stone show that the mechanical properties of cement stone can be greatly improved by modified whisker,and the mechanism of modified whisker in cement stone is analyzed by XRD and SEM.XRD results show that the modified whisker affects the hydration reaction of cement.SEM images show that in the modified whisker cement paste,there are more particles attached to the surface of the extracted whisker,but there is no such phenomenon in the ordinary whisker cement paste,which explains from many aspects that the modified whisker has more significant enhancement effect on the mechanical properties of cement paste. |
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