Study On The Improvement Of The Mechanical Properties Of Cementing Stone And Its Action Mechanism By Whisker Materials

In cementing engineering,the cement sheath formed between casing and formation is the key factor to ensure the subsequent safe drilling and oil and gas wells efficient production,keeping the cement sheath integrity is very important to the interlayer sealing ability.Oil well cement belongs to brittle material,it has the characteristics of brittle fracture,low splitting tensile strength and poor impact resistance.It is easy to produce micro-cracks in underground,which results in the decrease of cement ring sealing ability.With the increasing difficulty of petroleum exploration and development,the working conditions of cementing operations are becoming more and more complex.Therefore,toughening materials are used to improve the microstructure of cement rings and improve the mechanical integrity and interlaminar sealing ability of cement rings.This paper systematically investigates the fiber/whisker toughening materials used in oil well cement paste,two kinds of whisker materials were used to reduce brittleness and toughen oil well cement stone and the effects of potassium whisker and aluminium whisker on mechanical properties and dynamic mechanical properties of oil well cement were investigated.The experimental results show that:the mechanical properties and impact resistance of cement paste can be improved by adding whiskers into oil well cement,and the elastic modulus of samples can be effectively reduced.After 28 days of curing with 1.5%potassium whisker in oil well cement,the compressive,tensile and flexural strength of the specimens increased by 23.3%,93.7%and 27.9%compared with the blank specimens.The elastic modulus of the specimens was 6281.7 MPa,and the ultimate strain was 4.48%.Compared with the blank specimens,the ultimate strain was reduced by 25.5%,and the ultimate strain was increased by 282.9%;After 28 days of curing,the compressive,tensile and flexural strength of 6%A1 whisker specimens increased by 32.1%,101.3%and 23.6%compared with blank specimens.The elastic modulus of the specimens was 7254.6 MPa and the ultimate strain was 3.56%,which decreased by 14.1%and increased by 204.2%compared with blank specimens.Testing results of dynamic mechanical properties of whisker cement paste show that:Under dynamic loading,whisker cement paste and blank cement paste exhibit strain rate effect,whisker addition can effectively improve the dynamic stress and strain of matrix;peak stress,peak strain and dynamic elastic modulus of each sample increase with strain rate in a weak power function,reflecting a strong rate dependence;whisker material addition can improve the dynamic reinforcement coefficient of matrix and improve it.In the blank cement paste,the strain rate sensitivity of the blank cement paste is lower than that of whisker cement paste;at low strain rate,whisker cement paste has a greater impact on the matrix toughness,and the toughness gap narrows with the increase of strain rate;whisker cement paste has a better energy dissipation capacity than blank cement paste,and can effectively reduce the degree of damage,whisker cement paste energy dissipation square Masks are more balanced in nature,so they have more advantages in bearing dynamic loads.Analysis of cement stone by TG,XRD,FIFR,SEM and pore size distribution.The effect of whisker addition on the microstructure and phase composition of oil well cement paste was studied.The test results show:the addition of potassium whisker and aluminium whisker will not affect the hydration products and hydration process of cement paste,it can slightly reduce the content of CH and improve the pore distribution of cement stone;Hydration products will adhere to the surface of whiskers,which strengthens the bonding force between whiskers and cement matrix.The filling effect,crack deflection,the pullout,and the whisker bridging were regarded as effective mechanisms for the addition of whisker when improving the mechanical properties of oil-well cementThe addition of potassium whisker and aluminium whisker can effectively improve the mechanical properties,impact strength and microstructure of oil well cement paste.With the extension of oil and gas exploration to deep,low permeability,ocean and unconventional fields,especially under the situation of popularization and application of large-scale volume fracturing in shale gas wells.The requirement for the toughness of cement stone is getting higher and higher in engineering.The whisker toughening materials and corresponding technologies for cement stone will have a broader application prospect.