Xiaowei Cheng

Synthesis and performance of itaconic acid/acrylamide/sodium styrene sulfonate as a self-adapting retarder for oil well cement

A novel self-adapting retarder itaconic acid/acrylamide/sodium styrene sulfonate (IA/AM/SSS, hereinafter referred to as PIAS) was synthesized by free-radical, aqueous-solution polymerization and characterized by FTIR and TG. The optimum reaction conditions of polymerization were obtained from orthogonal experiments (L33) and subsequent data analysis. According to the evaluation as a retarder, the PIAS made it possible to obtain both a long thickening time and a swift compressive strength development for cement slurry, and therefore the applicable range of bottom hole circulation temperatures to the cement slurry has been widened to 60–180 °C. Moreover, the working mechanism of the self-adapting retarder PIAS was found to rely on the change of spatial structure of the molecules to retard the hydration of the cement. This paper also expounds that the delayed coagulation of the cement slurry is attributed to adsorption, chelation and “poisoning” effects of the PIAS molecules on the surface of hydrated particles or ions through XRD and SEM analyses.

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.

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.