Attempts to reduce the amount of greenhouse gases released into the atmosphere in recent years have led to the development of Carbon Capture and Sequestration(CCS)technology.However,there have been many studies report...Attempts to reduce the amount of greenhouse gases released into the atmosphere in recent years have led to the development of Carbon Capture and Sequestration(CCS)technology.However,there have been many studies reporting leakages form CO2 storage sites as a result of cement degradation induced by generation of an acidic environment in the storage site.Although there are a number of approaches proposed to enhance the efficiency of the cement,the degradation issue has not been totally resolved yet perhaps due to the excessive corrosives nature of carbonic acid and supercritical CO2.The aim of this study is to propose a methodology to improve the physical and mechanical characteristics of the cement by nanomodification such that a consistent rheology,constant density and a good strength development can be achieved.A new dispersion technique was proposed to ensure that the cement formulation gives a consistent result.The results obtained indicated that unlike the literature mixing,cement slurries prepared by the new mixing technique are very consistent in their rheology,regardless of the sonication parameters chosen.The measurements of the compressive strength performed at the reservoir condition revealed that nanosilica contributes in the strength development up to a certain point.Thermogravimetric Analysis(TGA)conducted at the last stage indicated that the amount of Portlandite left in the cement by adding nanosilica is decreased due to the pozzolanic reaction,which would help the cement to have a higher chance of survival in a storage site.However,cautions must be taken to maintain a certain amount of Portlandite in the cement for slowing down the carbonation rate,as otherwise the matrix of the cement is attacked directly and the cement will be degraded very fast.展开更多
To address present concerns about thickening time and high early-strength in deepwater cementing at low temperatures when using conventional accelerators, a new type of set-accelerating admixture comprising of lithium...To address present concerns about thickening time and high early-strength in deepwater cementing at low temperatures when using conventional accelerators, a new type of set-accelerating admixture comprising of lithium chloride, aluminium hydroxide and alkaline metal chlorides, named as LS-A, was studied in this paper. Mechanism analysis and performance tests show that the accelerator LS-A accelerated the hydration of tri- and dicalcium silicates （C3S and C2S） at low-temperatures by speeding up the breakdown of the protective hydration film and shortening the hydration induction period. Therefore, LS-A could shorten the low-temperature thickening time and the transition time of critical gel strength from 48 to 240 Pa of the Class-G cement slurry, and improve the early compressive strength of set cement at low-temperatures. It exhibited better performance than calcium chloride and had no effect on the type of hydration products, which remain the same as those of neat Class-G cement, i.e. the calcium silicate gel, Ca（OH）2 crystals and a small amount of ettringite AFt crystals. LS-A provides an effective way to guarantee the safety of cementing operations, and to solve the problems of low temperature and shallow water/gas flowing faced in deepwater cementing.展开更多
文摘Attempts to reduce the amount of greenhouse gases released into the atmosphere in recent years have led to the development of Carbon Capture and Sequestration(CCS)technology.However,there have been many studies reporting leakages form CO2 storage sites as a result of cement degradation induced by generation of an acidic environment in the storage site.Although there are a number of approaches proposed to enhance the efficiency of the cement,the degradation issue has not been totally resolved yet perhaps due to the excessive corrosives nature of carbonic acid and supercritical CO2.The aim of this study is to propose a methodology to improve the physical and mechanical characteristics of the cement by nanomodification such that a consistent rheology,constant density and a good strength development can be achieved.A new dispersion technique was proposed to ensure that the cement formulation gives a consistent result.The results obtained indicated that unlike the literature mixing,cement slurries prepared by the new mixing technique are very consistent in their rheology,regardless of the sonication parameters chosen.The measurements of the compressive strength performed at the reservoir condition revealed that nanosilica contributes in the strength development up to a certain point.Thermogravimetric Analysis(TGA)conducted at the last stage indicated that the amount of Portlandite left in the cement by adding nanosilica is decreased due to the pozzolanic reaction,which would help the cement to have a higher chance of survival in a storage site.However,cautions must be taken to maintain a certain amount of Portlandite in the cement for slowing down the carbonation rate,as otherwise the matrix of the cement is attacked directly and the cement will be degraded very fast.
基金provided by the Ph.D.Programs Foundation of Ministry of Education of China(Grant No.20100133120004)National Major Science and TechnologyProject of China(Grant No.2009ZX05060)National High Technology Research and Development Programof China(863program,Grant No.2006AA09Z340)
文摘To address present concerns about thickening time and high early-strength in deepwater cementing at low temperatures when using conventional accelerators, a new type of set-accelerating admixture comprising of lithium chloride, aluminium hydroxide and alkaline metal chlorides, named as LS-A, was studied in this paper. Mechanism analysis and performance tests show that the accelerator LS-A accelerated the hydration of tri- and dicalcium silicates （C3S and C2S） at low-temperatures by speeding up the breakdown of the protective hydration film and shortening the hydration induction period. Therefore, LS-A could shorten the low-temperature thickening time and the transition time of critical gel strength from 48 to 240 Pa of the Class-G cement slurry, and improve the early compressive strength of set cement at low-temperatures. It exhibited better performance than calcium chloride and had no effect on the type of hydration products, which remain the same as those of neat Class-G cement, i.e. the calcium silicate gel, Ca（OH）2 crystals and a small amount of ettringite AFt crystals. LS-A provides an effective way to guarantee the safety of cementing operations, and to solve the problems of low temperature and shallow water/gas flowing faced in deepwater cementing.
