Multi-scale Inorganic Whisker Reinforcement Oil Well Cement-based Materials And Mechanism Research

The property of cement sheath is key factor which affect the subsequent resources exploitation and storage in the oil and gas well engineering.And the demand for the properties of cement sheath goes higher and higher with the exploitation of oil and gas gradually moving to deep water,unconventional and high salt formation;and the cement-based materials belongs to brittle materials,of which has a higher compressive strength and elastic modulus and lower tensile strength,which results in the relatively obvious brittle characteristics in the fracture failure process.And the stress from drilling,perforation and fracturing brings a lot of micro-cracks in cement,which reduces the capacity of cementing fluid between the layers,leading to the destruction of the cementing integrity.Therefore,it is significant to research the improvement of cement-based materials in mechanical property and microstructure.Based on the investigation of predecessors' research results,different sizes of silicic whiskers has been used to improve mechanical property according to the multiscale effect of microscope crack initiation and expansion.And the category A silicic whisker with diameter less than 500nm and length between 10-30?m,and category B silicic whiskers with diameter between 500-2500nm and length between 200-300?m and both mix whiskers have been used to improve the mechanical property of oil well cement.According to the results,the silicic whiskers can effectively increase the mechanical property.And compared to virgin cement,the compressive strength,tensile strength and flexural strength of the samples with 1%addition of category A silicic whiskers increased 19%,100%and 34%and the ultimate strain is more than 5%,which increase 194%,and the elasticity modulus is 4648.4MPa which decrease 31.1%after 28 days curing;While compared to virgin cement,the compressive strength,tensile strength and flexural strength of the samples with 2%addition of category B silicic whiskers increased 9%?104%and 26%and the ultimate strain is 4.2%,which increase 147%,and the elasticity modulus is 5429.3MPa which decreasel9.5%after 28 days curing;And compared to virgin cement,the compressive strength,tensile strength and flexural strength of the samples with mix whiskers(1%A whiskers and 2%B whiskers)increased 21%?129%and 42%,and the ultimate strain is 6%,which increase 253%,and the elasticity modulus is 4027.6MPa which decrease40.3%after 28 days curing.To discuss the influence of silicic whiskers on the hydration process,the x-ray diffraction,infrared spectroscopic analysis,scanning electron microscope and mercury intrusion pore distribution had been used to test all samples.And the results shows that,the different scale silicic whiskers cannot affect the hydration process and hydration products,and some hydration products adhere to category A whiskers in SEM photograph,indicates the good compatibility between category A whiskers and hydration particles,which make for the bridge,deflection and pull out the effect of A-whiskers to improve the mechanical properties.And the category B whiskers can consume the destructive energy through its larger surface area and perfect strength.While these two whiskers can restrict the crack propagation in different size scale,resulting in an enhanced synergism to increase the mechanical properties effectively.In generally,both of the silicic whiskers could reinforce the properties and microstructure of oil-well cement composites.They could remain the mechanical intergrity and provide a theory base on the application in oil well cement in the future.