The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy...The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy development. Previous attempts to address this problem has been unsatisfactory because they can only reduce the strength decline rate. This study presents a new solution to this problem by incorporating fly ash to the traditional silica-cement systems. The influences of fly ash and silica on the strength retrogression behavior of oil well cement systems directly set and cured under the condition of 200°C and 50 MPa are investigated. Test results indicate that the slurries containing only silica or fly ash experience severe strength retrogression from 2 to 30 d curing, while the slurries containing both fly ash and silica experience strength enhancement from 2 to 90 d. The strength test results are corroborated by further evidences from permeability tests as well as microstructure analysis of set cement. Composition of set cement evaluated by quantitative X-ray diffraction analyses with partial or no known crystal structure(PONKCS) method and thermogravimetry analyses revealed that the conversion of amorphous C-(A)-S-H to crystalline phases is the primary cause of long-term strength retrogression.The addition of fly ash can reduce the initial amount of C-(A)-S-H in the set cement, and its combined use with silica can prevent the crystallization of C-(A)-S-H, which is believed to be the working mechanism of this new admixture in improving long-term strength stability of oil well cement systems.展开更多
A sustainable waste management system requires the beneficial uses of waste residues, such as sludge and incineration ashes, generated from environmental treatments. Among the use strategies, the practices of mixing h...A sustainable waste management system requires the beneficial uses of waste residues, such as sludge and incineration ashes, generated from environmental treatments. Among the use strategies, the practices of mixing hazardous metal-bearing solids with clay materials to produce ceramic products are often found with significant improvement in reducing the metal leach ability from products. However, relatively much fewer studies have clearly answered the questions of "What are the metal stabilization mechanisms other than simply the dilution effect and the encapsulation of metals?"; "What are the mineral phases of metals and how much are they in the products?"; and "How thermal conditions can effetely promote the transformations of metal-hosting mineral phases?". As many sustainability movements have increasingly promoted the adoption of those products generated from the beneficial use of waste materials, quantitative understandings of the metal incorporation efficiencies are important to facilitate the design of safe and reliable waste-to-resource strategies. Current findings on the metal incorporation mechanisms between common alumino silicates and hazardous metals (nickel, copper, and zinc) under different thermal conditions will be presented, and the results show the important role of forming aluminates and ferrites to significantly reduce the metal leach ability from the products. In the study, the technique of quantitative X-ray diffraction (QXRD) was applied to report the metal incorporation efficiencies through a 3-hour sintering process, aiming to stabilize the hazardous metals and also to turn the waste residues for usable ceramic products. Prolonged leach tests for potential metal-containing phases were carried out in acidic environments to evaluate the durability of thermally treated products. Both aluminate and ferrite spinels proved superior for thermomobilization of hazardous metals. With the information reported, this study has identified the key mechanisms of stabilizing the hazardous metals when thermally treated with common ceramic raw materials, and also demonstrates the importance of quantitative understanding in the development of a safe waste-to-resource strategy.展开更多
基金National Natural Science Foundation of China(No.51974352 and No.52288101)China University of Petroleum(East China)(No.2018000025 and No.2019000011)。
文摘The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy development. Previous attempts to address this problem has been unsatisfactory because they can only reduce the strength decline rate. This study presents a new solution to this problem by incorporating fly ash to the traditional silica-cement systems. The influences of fly ash and silica on the strength retrogression behavior of oil well cement systems directly set and cured under the condition of 200°C and 50 MPa are investigated. Test results indicate that the slurries containing only silica or fly ash experience severe strength retrogression from 2 to 30 d curing, while the slurries containing both fly ash and silica experience strength enhancement from 2 to 90 d. The strength test results are corroborated by further evidences from permeability tests as well as microstructure analysis of set cement. Composition of set cement evaluated by quantitative X-ray diffraction analyses with partial or no known crystal structure(PONKCS) method and thermogravimetry analyses revealed that the conversion of amorphous C-(A)-S-H to crystalline phases is the primary cause of long-term strength retrogression.The addition of fly ash can reduce the initial amount of C-(A)-S-H in the set cement, and its combined use with silica can prevent the crystallization of C-(A)-S-H, which is believed to be the working mechanism of this new admixture in improving long-term strength stability of oil well cement systems.
文摘A sustainable waste management system requires the beneficial uses of waste residues, such as sludge and incineration ashes, generated from environmental treatments. Among the use strategies, the practices of mixing hazardous metal-bearing solids with clay materials to produce ceramic products are often found with significant improvement in reducing the metal leach ability from products. However, relatively much fewer studies have clearly answered the questions of "What are the metal stabilization mechanisms other than simply the dilution effect and the encapsulation of metals?"; "What are the mineral phases of metals and how much are they in the products?"; and "How thermal conditions can effetely promote the transformations of metal-hosting mineral phases?". As many sustainability movements have increasingly promoted the adoption of those products generated from the beneficial use of waste materials, quantitative understandings of the metal incorporation efficiencies are important to facilitate the design of safe and reliable waste-to-resource strategies. Current findings on the metal incorporation mechanisms between common alumino silicates and hazardous metals (nickel, copper, and zinc) under different thermal conditions will be presented, and the results show the important role of forming aluminates and ferrites to significantly reduce the metal leach ability from the products. In the study, the technique of quantitative X-ray diffraction (QXRD) was applied to report the metal incorporation efficiencies through a 3-hour sintering process, aiming to stabilize the hazardous metals and also to turn the waste residues for usable ceramic products. Prolonged leach tests for potential metal-containing phases were carried out in acidic environments to evaluate the durability of thermally treated products. Both aluminate and ferrite spinels proved superior for thermomobilization of hazardous metals. With the information reported, this study has identified the key mechanisms of stabilizing the hazardous metals when thermally treated with common ceramic raw materials, and also demonstrates the importance of quantitative understanding in the development of a safe waste-to-resource strategy.
