Zaoyuan Li

Time effectiveness of the low-temperature plasma surface modification of ground tire rubber powder

Recycling of waste tire has great practical significance. This paper reports results from studies carried out to determine the time effectiveness of the low-temperature plasma surface modification of ground tire rubber (GTR). Attenuated total reflectance Fourier transform infrared spectroscopy showed that plasma treatment activated the powder surface. The X-ray photoelectron spectroscopy analysis showed an increase in oxygen and carbon element ratio. Meanwhile, the scanning electron microscopy analysis indicated a slight increase in the surface roughness of the treated powder. Testing its hydrophilic property in water indicated that the GTR powder showed decreased dispersive capacity as the time lengthened. Mechanical tests showed that the strength and toughness of the cement stone reduced slightly as a result of increased storage time.

Characterization of the unidirectional corrosion of oilwell cement exposed to H2S under high-sulfur gas reservoir conditions

The corrosion of H2S on oilwell cement is considered to be a great challenge for wellbore integrity and environmental safety in the exploitation of high-sulfur gas reservoirs. In this study, the corrosion performance of oilwell cement exposed to humid H2S gas and H2S-rich brine was investigated using designed unidirectional samples. Compressive strength, microhardness, porosity, gas permeability, SEM, EDS, and XRD analyses were conducted to compare the dissimilarity of H2S attack in the two exposure scenarios. The experimental results show that the corrosion degree of cement exposed to humid H2S gas was lower due to the dense gypsum layer formed on the cement surface and this layer inhibited the inward penetration of H2S by blocking its diffusion. On the contrary, a porous and loose amorphous silica gel section was formed on the headspace of the brine-exposed cement due to the dissolution and migration effects of brine, which facilitated the penetration of H2S to the interior of the cement. The degradation mechanism of cement and the effects of exposure scenario on cement properties are proposed.

Influence of potassium titanate whisker on the mechanical properties and microstructure of calcium aluminate cement for in situ combustion

Abstract This study investigated potassium titanate whisker-reinforced calcium aluminate cement (CAC)-based composites, and evaluated the influence of the quantity (0–5% of the weight of the binder) of potassium titanate whiskers on the mechanical properties of hardened cement mortar. X-ray diffraction analysis and Scanning electron microscopy (SEM) were employed to determine the phase compositions and micro-morphology of the cement composites, respectively. Experimental results indicated that the addition of potassium titanate whisker exhibits significant potential to improve the tensile strength and toughness of cement mortars. The compressive and tensile strengths of samples cured at 50 °C were increased by 46.90 and 74.10%, and the tensile strength samples under high-temperature treatment increased by 113.67%, with the addition of 4% potassium titanate whisker. Typical cement slurry properties, such as basic rheology, free water, and fluid loss could maintain stability when added with 0–5% dosages of potassium titanate whiskers. SEM analysis indicated that the whisker could increase the toughness of oil cement, which contributed to whisker pullout and whisker-cement coalition pullout in the cement matrix.

The influence of sulfomethyl phenol formaldehyde resin (SMP) on cementing slurry

The poor compatibility between drilling fluid additives and cementing slurry can lead to downhole accidents and inferior cementing quality. Therefore, this paper intends to study on the influence of sulfomethyl phenol formaldehyde resin (SMP) on cement slurry. This paper studies the influence of SMP on the rheological property, thickening time, aggregate stability of cement slurry, and compressive strength of cement stone, and studies the influence of SMP on the concentration of metal ions of cement slurry. And this paper analyzes the influence of SMP on the microstructure of cement slurry via vacuum freeze-dry technology of liquefied nitrogen combined with environmental scanning electron microscope. Finally draw the conclusions: SMP and metal ions with high valence (Fe3+, etc.) set off complexation reaction in cement slurry, which increases the molecular weight of complex compound adsorbed on the surface of the cement particles. Meanwhile, Zeta potential is decreased after SMP is added to cement slurry, and the cement slurry becomes thickened as the particles move from agglomeration and diffusion equilibrium towards aggregation direction. After SMP and metal ions with high valence (Fe3+, … etc.) set off the complexation reaction in cement slurry, a dense “film” is formed on the surface of the particles to prevent cement particles from contacting free water, which will reduce the hydration rate of cement particles, increase the thickening time of cement slurry, and reduce the compressive strength of the cement stone to only two-fifth of the compressive strength of cement stone with original formula.

Relationship Between the Microstructure/Pore Structure of Oil-Well Cement and Hydrostatic Pressure

In cementing operations, hydrostatic pressure reduction in cement slurries is a serious threat to operation safety and cementing quality. This study combines X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, low-field nuclear magnetic resonance, and nano-computed tomography to investigate the mechanism of hydrostatic pressure reduction in cement slurries. The experimental results reveal that hydrostatic pressure transmission in a fresh cement slurry follows Pascal’s law. However, in the slurry, some cement particles undergo sedimentation with an increase in the hydration time, which reduces a part of the hydrostatic pressure. Further, another part of the hydrostatic pressure, which is maintained by the free water in the slurry pores, is reduced during the hardening stage. When the hydration reaction of the slurry is accelerated, the pore water in the slurry is supersaturated and hydration products start to rapidly nucleate and grow between the cement particles. These hydration products are porous gel structures and can change the pore structure of the cement slurry; a macro-pore is divided into many micropores, such as capillary pores and gel pores. Because these pores are filled by water in the slurry, during this process, free water in the macro-pores is changed to capillary water and gel water. However, gel water and capillary water cannot transmit hydrostatic pressure in the cement slurry. Meanwhile, in the fresh cement slurry, many pores containing free water are connected and some hydration products rapidly grow in the macro-pores and fill them, which may reduce the column height of the free water in the pores and lead to hydrostatic pressure reduction in the slurry.

Synthesis of microcrystalline brownmillerite Ca2(Al,Fe)2O5 and its influence of mechanical properties to the class G oil-well cement

Abstract This study investigated the use of calcium oxide (CaO), aluminum oxide (Al2O3) and ferric oxide (Fe2O3) as raw materials for the production of brownmillerite Ca2(Al,Fe)2O5, after firing at 1330, 1350 and 1370 °C. Lithofacies analysis, SEM/EDS and XRD were used to analyze the phase transition and microstructure of the clinkers during the firing process, and the contents of free calcium oxide (f-CaO) in the clinkers were determined by chemical titration. The results showed that the optimum temperature for the preparation of brownmillerite was 1370 °C (within the selected temperature range). By firing and quenching, microcrystalline brownmillerite (MB) was obtained (crystallinity index was 0.7). Compared with the compressive strength of class G oil-well cement matrix (M0) without MB, the compressive strength of specimens (M4) with 4 wt% MB addition increased by 67, 12, 20 and 33% (after curing for 1, 3, 7 and 14 d, respectively). meanwhile, the elastic modulus of M4 (after curing for 7 d) was reduced by 24% relative to that of M0, indicating that the mechanical properties of M4 were better than that of M0. To investigate the effect of microcrystalline brownmillerite on the strength and toughness of the class G oil-well cement matrix, triaxial testing was used in this study, and the toughening mechanisms were established.

The Slag Influence on High Temperature Resistance of Aluminophosphate Cementfor Heavy Oil Thermal Recovery

Abstract The sharp strength recession of silicate cement in high temperature is the crucial reason of casings damage and zonal isolation failure in heavy oil thermal recovery. Although aluminophosphate cement has a better high temperature resistance in comparison with silicate cement, its compressive strength recession in high temperature slightly recessed. The results show that adding slag into aluminophosphate cement can not only develop compressive strength of cement at low temperature, but it can also improve the high temperature resistance of the cement. After adding slag, the formation of C2ASH8 conduces to develop cement strength at low temperature, and C3AS2H2 conduces to high temperature resistance. To increase temperature resistance of aluminophosphate cement, C3ASH4 generation and Al(OH)3 decomposition should be avoided. Crystal structure of cement after high temperature is well developed with compactly and neatly arranged, allowing cement to maintain good mechanical properties to help protect the casing and improve zonal isolation performance.