A Comprehensive Method for the Optimization of Cement Slurry and to Avoid Air Channeling in High Temperature and High-Pressure Conditions

Air channeling in the annulus between the casing and the cement sheath and/or between the cement sheath and formation is the main factor affecting the safe operation of natural gas wells at high temperatures and pressures.Prevention of this problem requires,in general,excellent anti-channeling performances of the cement sheath.Three methods to predict such anti-channeling performances are proposed here,which use the weightless pressure of cement slurry,the permeability of cement stone and the volume expansion rate of cement sheath as input parameters.Guided by this approach,the anti-channeling performances of the cement slurry are evaluated by means of indoor experiments,and the cement slurry is optimized accordingly.The results show that the dangerous transition time of the cement slurry with optimized dosage of admixture is only 76 min,the permeability of cement stone is 0.005 md,the volume shrinkage at final setting is only 0.72%,and the anti-channeling performances are therefore maximized.The effective utilization of the optimized cement slurry in some representative wells(LD10–1-A1 and LD10–1-A2 in LD10–1 gas field)is also discussed.

Infl uences of Iodonium Salts on the Properties of a Hybrid Composite Resin Containing Bis S-GMA and Expanding Monomer Modifi ed Epoxy

In order to reduce shrinkage and improve the mechanical properties of dental composite resins, we designed a hybrid resin formulation containing a novel matrix resin, Bis S-GMA [bisphenol-Sbis（3-methacrylato-2-hydroxypropyl）ether], and epoxy modifi ed by a spiro-orthocarbonate（SOC） expanding monomer. Then, we tested the effects of an iodonium salt, diphenyliodonium hexafl uorphosphate（DPIHFP）, on the properties of the hybrid resin with seven different concentrations. The hybrid resin was polymerized by a ternary photo-initiator system. The volumetric shrinkage（VS）, degree of conversion（DC） and compressive strength（CS） were assessed using Acu Vol^TM, FTIR and a universal testing machine, respectively. The VS, DC and CS were improved with increasing DPIHFP concentration, but a high concentration of DPIHFP had a negative infl uence on the mechanical properties of the hybrid resin and offered no added improvement in the VS and DC. The best performance of a composite resin containing Bis S-GMA and SOC-modifi ed epoxy was achieved with 2wt% DPIHFP. The results also indicated that the resin containing Bis S-GMA was superior to that containing Bis-GMA in terms of VS, DC and CS.

Carbothermic reduction behaviors of Ti–Nb-bearing Fe concentrate from Bayan Obo ore in China

To support the development of technology to utilize low-grade Ti-Nb-bearing Fe concentrate, the reduction of the concentrate by coal was systematically investigated in the present paper. A liquid phase formed when the Ti Nb-bearing Fe concentrate/coal composite pel- let was reduced at temperatures greater than 1100℃. The addition of CaCO3 improved the reduction rate when the slag basicity was less than 1.0 and inhibited the formation of the liquid phase. Mechanical milling obviously increased the metallization degree compared with that of the standard pellet when reduced under the same conditions. Evolution of the mineral phase composition and microstructure of the reduced Ti-Nb-bearing Fe concentrate/coal composite pellet at 1100~C were analyzed by X-ray diffraction and scanning electron microsco- py-energy-dispersive spectroscopy. The volume shrinkage value of the reduced Ti-Nb-bearing Fe concentrate/coal composite pellet with a basicity of 1.0 was approximately 35.2% when the pellet was reduced at 1100℃ for 20 min, which enhanced the external heat transfer to the lower layers when reduced in a practical rotary hearth furnace. The present work provides key parameters and mechanism understanding for the development of carbothermic reduction technology of a Ti-Nb-bearing Fe concentrate incorporated in a pyrometallurgical utilization flow sheet.

Investigation on Thermal and Dimensional Stability of Epoxy Resin In-Situ Modified by Cyanate Ester Resin and Polydimethylsiloxane

The thermal and dimensional stability of epoxy resin(EP)in-situ modified by cyanate ester(CE)and polydimethylsiloxane(PDMS)are investigated by means of experiments and numerical simulation.Thermal gravimetric analysis(TGA)and differential scanning calorimeter(DSC)are used to analyze the heat resistance of the modified EP.The dimensional stability is characterized by the volume shrinkage of the series PDMS/CE/EP obtained by the density method.The chemical structure of the PDMS/CE/EP is analyzed by Fourier transform infrared spectroscopy(FTIR).The results of TGA and DSC indicate that the thermal stability of PDMS/CE/EP decreases firstly and then increases with the increase in the amount of CE.The addition of PDMS shows a slight effect on the thermal stability.The 40%CE makes the blending system exhibit the lowest initial decomposition temperature,which reduces by 15.5%and 40.8%compared with pure EP and CE,respectively.The FTIR results suggested that the influence of CE on the thermal stability of the modified EP is mainly ascribed to the generation of oxazolidinone ring with low thermal stability and the increase in the triazine ring with high thermal stability.The volume shrinkage measurement results show that the introduction of CE and PDMS are both beneficial to the improvement of the dimensional stability of the blending systems.The in-situ addition of 80%CE shows the lowest volume shrinkage of6.11%.The thermal stress distribution of PDMS/CE/EP generated during the solidification process is simulated by the finite element analysis.The results suggested that the introduction of 80%CE into EP results in the lowest thermal stress in the blending system,which indicates that the system has the lowest volume shrinkage,which agrees well with the experimental results.

Recyclable Joule heated low shrinkage carbon nanofiber aerogels for microscale oil/water separation

Aerogels have shown great potential as oil adsorbents but their application to the removal of microscale oil from water and their recycling remains problematic.The present work proposed a freeze-shaping method for fabricating carbon nanofiber aerogels(CNFAs)based on the direct use of one-dimensional(1D)carbon nanofibers(CNF)rather than carbonization of polymer aerogels.This technique greatly reduces volume shrinkage and increases the three-dimensional(3D)structural stability of the material.Carbon nanotubes(CNT)and gelatinized starch were incorporated in these aerogels as a conductive enhancement agent and binder,respectively,forming a“vine(CNT)-wrapped tree(CNF)”structure that improved mechanical and Joule-heating performance.The effects of glutaraldehyde added to aerogels as a crosslinking agent on mechanical properties and microstructure were also systematically investigated.The optimized CNFAs combined with low density,high porosity,good elasticity,and superior Joule-heating efficiency along with suitable adsorption capacity,excellent selectivity,and cycling stability.This material was able to selectively remove 87%and 92%of microscale acetone and dimethylformamide(DMF),respectively,from the water after nine cycles of adsorption and Joule-heating.The present work demonstrates a novel means of designing and fabricating a low shrinkage CNFA with outstanding Joule-heating performance having potential practical applications in the remediation of organic pollution.