The Effect Of Whisker-like Calcium Carbonate And Compound Micro-silicon On The Anti-cracking Properties Of Cement

Slurry is pumped into the bottom of hole by pumper, annulus breakthrough flow will cause packing failure between layers,which influence safely exploiting and developing of oilfield. Cement slurry loss of weight lead to the pressure of fluid column decrease by degree.In the process of the hardened cement, oil-well cement gains a volumetric shrinkage. Micro-annulus and micro-fissure are attributed to the tensile stress between the interface of casing and borehole wall,the fluid channeling happens along the channel of micro-annulus and micro-fissure. Portland cement is a kind of natural brittle material, with poor anti-tensile strength and anti-impact fracture. Perforating and stimulation operations of oil and gas well will destroy the integrity of cement, forming macroscopic crack and channeling path. Now,we usually slove the above problems by main means of adminxture for cement slurry.However,It has been found that admixture for cement improve anti-channeling performance is limtied. Therefore, seeking a new admixture for cement and studing the physical and chemical properties on admixture has a positive significance for prevention of annulus flow.Calcium carbonate whisker is a new type inorganic mineral materials on the basis of nanometer calcium carbonate. Calcium carbonate whisker has advantages as low cost,high heat stability, high young's modulus, high aspect ratio, a double nature of mineral powder and fiber. In this paper, According to the advantages the two types of admixtures, calcium carbonate whisker and micro-silicon commonly improve performance of oil well cement anti-channeling. In this research, the researcher have chose the SPN and Cement resistance coefficient method to evaluate cement channeling prevention performance, comparator method to evaluate the volume shrinkage of cement solidified body, Brittleness coefficient characterize the brittleness. Observing the cement microstructure by DKS-? and SEM. Laboratory research gets the following conclusion:(1) Effect on the properties of cement channeling prevention by mixing calcium carbonate whisker only. Mixing calcium carbonate whisker into cement can improve the cement's channeling prevention performance, reduce cement stone brittleness and volume shrinkage. The dosage of whisker is closely linked with cement channeling prevention ability, when the dosage of whisker admixture is more than 20%, the fluidity of cement paste become worse, and no longer has the construction. When whisker content reaches 6%, the SPN value and cement volume shrinkage in 7 days are minimum, and cement embrittlement reduces greatly.(2) Effect on the properties of cement channeling prevention by mixing micro silicon only. Mixing micro silicon into cement can improve the cement's channeling prevention performance, reduce cement stone brittleness and increase volume shrinkage. Mixing micro silicon into cement at the temperature of 90 and 110?, when the dosage reaches 20%, the SPN value and cement embrittlement is minimum. The volume contraction of compounds which dosage are 5%,10%,15% and 20%, is greater than that of basic formula.(3) Mixing calcium carbonate whisker and micro silicon. Mixing calcium carbonate whisker and micro silicon into cement can improve the cement's channeling prevention performance, reduce cement stone brittleness and increase volume shrinkage, which is higher than the contribution of mixing calcium carbonate whisker and micro silicon separately. Curing under 110? for 7 days, cement expand, the C-H-S gel generated by the hydration reaction between micro silicon and cement improved the transition interface between the cement and whisker effectively, improved the mechanical properties of cement and increase the degree of compacted cement further.(4) About the influence of porosity and permeability. Adding the calcium carbonate whisker, micro silicon separately and the both under the temperature of 90? and 110? for 3 days, the porosity and permeability are less than that of basic formula.(5) Channeling prevention mechanism of whisker and micro silicon. Calcium carbonate whisker can play the role of filler and bridges. The C-H-S gel generated by the reaction between micro silicon and cement hydration product CH improved the transition interface between the cement and whisker effectively. The generated calcium silicate gel filled pore structure of cement slurry, improved the mechanical properties of cement, reduce the drying shrinkage of cement stone, and increased the ability of fluid prevention.