In order to veritably measure the first peak of hydration heat evolution that has been illustrated important in indicating cement behavior in early hydration, an improved way of water addition into cement in isotherma...In order to veritably measure the first peak of hydration heat evolution that has been illustrated important in indicating cement behavior in early hydration, an improved way of water addition into cement in isothermally calorimetric experiment is put forward. The experimental results indicated that: the magnitude of first peak of heat evolution varies from sample to sample, correlation between heat evolution during first peak of heat evolution and initial (as well as final) setting time is unsatisfactory when samples are not classified; while groups of sample classified based on strength grade represent satisfactory correlations, which indicating the existence of close relation between hydration heat evolution in much earlier hydration age and setting property of cement in rather later age. Importance of first peak in hydration heat evolution for understanding cement setting property and reasons for sample classification are also discussed in this paper.展开更多
Low alkaline liquid state setting accelerator（LSA） for Portland cement was prepared in laboratory from aqueous solution of several inorganic sulfate salts and some organic chemical substances. Properties of cement w...Low alkaline liquid state setting accelerator（LSA） for Portland cement was prepared in laboratory from aqueous solution of several inorganic sulfate salts and some organic chemical substances. Properties of cement with addition of LSA relating to its setting time and strength development as well as its resistance to sulfate attack for short and long term exposure were experimentally examined. The experimental results showed that 5%-7% addition of LSA significantly accelerated the initial and final setting of Portland cement in the presence or absence of the blending of mineral admixtures, the initial and final setting time being less than 3 min and 6 min respectively. Meanwhile, the early 1 day curing age compressive strength increased remarkably by 20%, while the late 28 th day curing age compressive strength remained almost unchanged as compared with that of the reference accelerator free cement mortar specimen. Furthermore, mortar specimens of cement added with LSA and exposed to 5% Na2SO4 solution showed their excellent resistance to sulfate attack, with their short and long term curing age resistance coefficient to sulfate attack being around 1.04 to 1.17, all larger than 1.0. XRD analysis on hardened cement paste specimens at very early curing ages of several minutes disclosed the existence of more ettringite in specimens added with LSA than that of the reference specimens, meanwhile SEM observation also revealed the existence of well crystallized ettringite at very early hydration stage, suggesting that the accelerated setting of Portland cement can be attributed to the early and rapid formation of ettringite over the whole cement paste matrix due to the introduction of LSA. MIP measurement revealed that hardened cement paste specimens with the addition of LSA presented less medium diameter pores, more proportion of small pores and less proportion of large capillary pores, which is in a very good coincidence with the improvement of strength development of cement mortars added with LSA.展开更多
Microsilica-gel bonded bauxite based no-cement refractory castables（NCCs）have been produced using two readily available dispersants.These NCCs were compared to NCC with Siox X-Zero,a purposely-developed product for ...Microsilica-gel bonded bauxite based no-cement refractory castables（NCCs）have been produced using two readily available dispersants.These NCCs were compared to NCC with Siox X-Zero,a purposely-developed product for microsilica-gel bonded no-cement castable systems to control flow properties and setting characteristics.Three mixing and curing temperatures were applied：5℃,20℃and 35℃.The results show that setting-behaviour and mechanical properties strongly vary with the type of dispersant and the curing temperature.However,both setting and strength are less temperature dependent in the castables with Siox X-Zero.Furthermore,the drying and firing of microsilica-gel bonded NCCs were investigated.Since microsilica-gel bond system contains only a small amount of bound water,the castables can be fired at very high heating rates,once the free water has been removed.展开更多
This study contains comparative research of sulfate resistance of ordinary Portland cement pastes with addition of basic aluminum sulfate (hydroxosulfate, Al(OH)1.78(SO4)0.61) and amorphous Al(OH)3. Over 3 months of s...This study contains comparative research of sulfate resistance of ordinary Portland cement pastes with addition of basic aluminum sulfate (hydroxosulfate, Al(OH)1.78(SO4)0.61) and amorphous Al(OH)3. Over 3 months of storing in sodium sulfate solution, the most significant expansion and deterioration occur in case of samples with aluminum hydroxide. During sulfate resistance test, the ratio between aluminum nuclei in AFt (ettringite) and AFm phases was studied by 27Al-MAS NMR, and the impact of aluminum-containing admixtures on this ratio was specified. In accordance with NMR data, in samples with Al(OH)3, the rate of secondary ettringite formation becomes noticeable after one month of storing in sulfate solution. For samples with Al(OH)1.78(SO4)0.61, the rate of elongation and temper of changes in molar ratio between sulfoaluminate phases were comparable with reference samples without admixtures.展开更多
The setting chemistry of glass ionomer cement was imestigated by using mechanical determination of compressive strength at predetermined intervals,and measurement of structure changes of correspondling fracture sample...The setting chemistry of glass ionomer cement was imestigated by using mechanical determination of compressive strength at predetermined intervals,and measurement of structure changes of correspondling fracture sample by means of IR spectra and differential scanning calorimetry（DSC）.Zinc polycarboxylate cement was used as a comparison sample.The compressive strength of glass ionomer cement（GIC） increases with aging.IR spectra and DSC of corresponding fracture sample show the structure changes of the matrix and interface layer comprising of silica gel during the predetermined intervals studied.however,no significant changes occur in the zinc polycarxyolate cement.Hence the structure changes of the matrix and/or interface layer are responsible for compressive strength increasing with aging.The structure changes include the crosslink density,the ratio of complex form to ionic form,the content ratio of Al-PAA to Ca-PAA,the forming and maturing process of the interface layer comprising of silica gel.展开更多
According to the characteristics of granular soil,the technological requirements of the special-purpose cement for stabilizing granular soil are put forward to meet the demands of implementation of highway base engine...According to the characteristics of granular soil,the technological requirements of the special-purpose cement for stabilizing granular soil are put forward to meet the demands of implementation of highway base engineering.A kind of slow-setting and slight-expansive cement is developed by the cross experiment method in slag-clinker-gypsum-alkaline system,the final setting time of the cement can be prolonged to 8h,and it has properties of low dry shrinkage,high flexural strength and good crack resistance.The strength of granular soil stabilized by the cement is increased by 20% compared with that stabilized by Chinese 425-Grade slag cement.展开更多
Brittle fracture of cement sheath, induced by perforation and stimulation treatments, can cause cross flow of formation fluid and increase casing damage. A novel agent XL was developed for solving the problem. Experim...Brittle fracture of cement sheath, induced by perforation and stimulation treatments, can cause cross flow of formation fluid and increase casing damage. A novel agent XL was developed for solving the problem. Experimental results showed that the toughness of the set cement containing XL was improved remarkably. The engineering properties of the slurry containing XL, drag reducer USZ （0.2% BWOC）, filtrate loss additive F 17B （1.2% BWOC） and crystalloid expanding agent F17A （3% BWOC） could meet technical requirements of cementing operation. After perforation, good quality cement sheath enhanced with XL was observed by CBL/VDL logs in a deep well.展开更多
Many measures, such as water injection, acid fracturing, thermal recovery, have been taken in the oilfield development. These can easily induce brittle fracture of set cement. Most of all, there are greater potential ...Many measures, such as water injection, acid fracturing, thermal recovery, have been taken in the oilfield development. These can easily induce brittle fracture of set cement. Most of all, there are greater potential for fractures in set cement in slim holes. Therefore, it is necessary to improve the toughness of the cement mantle. Results obtained from experiments show that carbon fiber, with a concentration of 0.12%-0.19% in cement and a length of 700 to 1,400μm, plays an important role in improving cement quality. Addition of carbon fiber can improve the bending strength of set cement by up to 30%. At the same time, the increase in fiber concentration can lower the elastic modulus and increase the Poisson＇s ratio of set cement. Thin-section analysis shows that fiber can effectively prevent the propagation of fractures and enhance the plasticity of the matrix and the ability to prevent fracture.展开更多
Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development.But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimu...Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development.But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimulation.In this paper,the shale gas development blocks in the Sichuan Basin were taken as the examples to explore the process and support measures that can be used to keep the mechanical integrity of cement sheath under the effect of hydraulic fracturing.It is indicated that the near-bit three-centralizer drifting BHA used for casing stiffness simulation can decrease the casing running difficulty in the long horizontal section of a shale gas well and increase the time efficiency and safety of casing running;that the flushing efficiency of high-efficiency oil flushing spacer fluid system is higher than 90%from room temperature to 120℃,so it can guarantee the displacement efficiency of cement slurry to the oil-based drilling fluid and the effective cementing of borehole wall;that the performance of anti-channeling ductile cement slurry used in the cementing of long horizontal sections in this area after it is set is confirmed,with the elastic modulus of set cement being lower than 7 GPa and triaxial strength being higher than 40 MPa,so as to alleviate or avoid the damage to cement sheath in the process of fracturing;and that cementing quality is improved by applying the support technologies,e.g.drilling fluid adjustment,pre-stress cementing and ground high-pressure pumping.During 2015e2016,these cementing technologies were applied in 85 wells in the Sichuan Basin.The average well depth of these wells is 4832 m,the average length of horizontal sections is 1560 m and the quality rate of well cementing is 89.58%.During the waiting-on-cement(WOC)time after well cementing,there is no sustained casing pressure.And gas channeling in the annulus during well drilling,completion and test is improved remarkably.It is concluded that this suite of technologies can guarantee and improve the cementing quality of long horizontal sections in shale gas wells and provides good cementing conditions for shale gas development.展开更多
With the development of cementing slurry technology,cementing self-healing has become one of the most effective technologies to prevent and treat oil and gas channeling and improve long-term sealing capacity of cement...With the development of cementing slurry technology,cementing self-healing has become one of the most effective technologies to prevent and treat oil and gas channeling and improve long-term sealing capacity of cement sheath.To solve the technical problem of annulus oil and gas channeling caused by the long-term sealing failure of cement sheath,this paper researches and develops a kind of viscosity-soluble type biomimetic self-healing cement slurry system from the perspective of chemical biomimetics,based on the technical idea of“prevention before blocking”.Then,the engineering performance of this biomimetic self-healing cement slurry system and the mechanical property of self-healing set cement are evaluated respectively.In addition,the mechanical recovery capacity and permeability reducing rate of the self-healing set cement conserved with methane are evaluated by creating fractures through splitting.Finally,the healing mechanisms of the self-healing cement are analyzed by means of SEM microscopic test and infrared spectrography.And the following research results are obtained.First,the set cement has excellent mechanical property.When the compressive strength decreases by 15%,the elastic modulus of set cement decreases by 41%,showing good toughness to play the role of“first prevention”.Second,when meeting hydrocarbon,the damaged set cement is excited to generate a kind of viscosity-soluble type gelatinous ester substance,which re-bonds the skeleton of the set cement.When the self-healing set cement is conserved with methane,its compressive strength recovery rate is up to 94.5%,bending strength recovery rate is 58.6%,gas log permeability drops by 99%,and liquid log permeability drops by 100%,so as to realize“blocking later”.In conclusion,the viscosity-soluble type biomimetic self-healing cement slurry system can effectively achieve cementing integrity and long-term sealing integrity through self-healing after the damage of cement sheath,which provides a strong technical support for preventing the production safety hazard of sustained casing pressure in oil and gas wells and is beneficial to solve the technical problem of annulus oil and gas channeling caused by long-term sealing failure of cement sheath.展开更多
At present,the mechanical testing on the ductility of cement sheath is faced with multiple technical difficulties.In this paper,numerical simulation and laboratory evaluation were adopted to compare the mechanical per...At present,the mechanical testing on the ductility of cement sheath is faced with multiple technical difficulties.In this paper,numerical simulation and laboratory evaluation were adopted to compare the mechanical performance of typical elastic,flexible,ductile and neat cement systems at home and abroad by different loading rates,value range of stress-strain curve,confining pressure and temperature.It is shown that when the loading rate is lower,the stress-strain curve of set cement is not smooth,but distorted,and the stress cannot be responded in time;that when the loading rate is higher,the stress-strain curve of set cement is smooth,and the yield stage is remarkable,indicating that higher loading rate can reflect the yield strain behavior of set cement more truly;that the recommended Young's modulus range of set cement should be changed based on the actual downhole conditions;that temperature has more effect on yield stress and ultimate strain,but less effect on elastic modulus;that confining pressure has more effect on ultimate stress and ultimate strain,but less effect on elastic modulus;and that when the confining pressure is lower and temperature is higher,the yield stage of set cement is more remarkable.It is concluded that these mechanical behaviors of cement system in different conditions provide a technical support for understanding the mechanical essence of downhole cement sheath and exploring the mechanical integrity of cement sheath and even that of the whole wellbore.展开更多
When well cementing is conducted in horizontal shale gas wells in Weiyuan block of the Weiyuan-Changning State Shale Demonstration Area,Sichuan Basin,the oil-based drilling fluid is not compatible with cement slurry,i...When well cementing is conducted in horizontal shale gas wells in Weiyuan block of the Weiyuan-Changning State Shale Demonstration Area,Sichuan Basin,the oil-based drilling fluid is not compatible with cement slurry,is difficult to be displaced because of its high density,and cement sheath tends to be broken in the situations of large-scale stimulated reservoir volume fracturing.In view of these problems,a series of studies were carried out specifically on the theoretical basis of cement sheath sealing mechanical parameters,oil-displacement preflush improving the interface cementation quality,toughness set cement satisfying large-scale fracturing requirements and cementing technology conducive to the wellbore integrity.The following achievements were made.First,the theoretical model of cement sheath mechanical integrity taking into account the plastic characteristics and interface cementation strength of cement sheath is instructive to the mechanical design of set cement for horizontal shale gas wells,avoiding the micro-annulus as much as possible.Second,oil-displacement preflush is developed and it is well compatible with oil-based drilling fluids and cement slurry with the flushing efficiency on oil-based drilling fluids higher than 90%.Third,the tough set cement which is developed based on the theoretical model of cement sheath sealing integrity not only guarantees higher compressive strength,but decreases Young's modulus by 30%.Forth,it is confirmed that water displacement cementing technology suitable for shale gas wells is conducive to improving the wellbore seal integrity.These research findings were applied in 12 horizontal wells.It is indicated that the quality cementing ratio of horizontal segment reaches 92%and the post fracturing effect is very good,which guarantees the sealing integrity of wellbores and provides a technical support for the highly efficient development of shale gas reservoirs.展开更多
As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen t...As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.展开更多
Grout injection is used for sealing or strengthening the ground in order to prevent water entrance or any failure after excavation.There are many methods of grouting.Permeation grouting is one of the most common types...Grout injection is used for sealing or strengthening the ground in order to prevent water entrance or any failure after excavation.There are many methods of grouting.Permeation grouting is one of the most common types in which the grout material is injected to the pore spaces of the ground.In grouting operations,the grout quality is important to achieve the best results.There are four main characteristics for a grout mixture including bleeding,setting time,strength,and viscosity.In this paper,we try to build some efficient grouting mixtures with different water to cement ratios considering these characteristics.The ingredients of grout mixtures built in this study are cement,water,bentonite,and some chemical additives such as sodium silicate,sodium carbonate,and triethanolamine(TEA).The grout mixtures are prepared for both of the sealing and strengthening purposes for a structural project.Effect of each abovementioned ingredient is profoundly investigated.Since each ingredient may have positive or negative aspect,an optimization of appropriate amount of each ingredient is determined.The optimization is based on 200 grout mixture samples with different percentages of ingredients.Finally,some of these grout mixtures are chosen for the introduced project.It should be mentioned that grouting operations depend on various factors such as pressure of injection,ground structure and grain size of soils.However,quality of a grout can be helpful to make an injection easier and reasonable.For example,during the injection,a wrong estimated setting time can destroy the injected grout by washing the grout or setting early which prevents grouting.This paper tries to show some tests in easy way to achieve a desirable sample of grout.展开更多
Regardless of the excellent properties of glass ionomer cements,their poor mechanical properties limit their applications to non-load bearing areas.This study aimed to investigate the effect of incorporated short,chop...Regardless of the excellent properties of glass ionomer cements,their poor mechanical properties limit their applications to non-load bearing areas.This study aimed to investigate the effect of incorporated short,chopped and randomly distributed flax fibers（0,0.5,1,2.5,5 and 25 wt%） on setting reaction kinetics,and mechanical and morphological properties of glass ionomer cements.Addition of flax fibers did not significantly affect the setting reaction extent.According to their content,flax fibers increased the compressive（from 148 to 250 MPa） and flexure strength（from 20 to 42 MPa）.They also changed the brittle behavior of glass ionomer cements to a plastic one.They significantly reduced the compressive（from 3 to 1.3 GPa） and flexure modulus（from 19 to 14 GPa）.Accordingly,flax fiber-modified glass ionomer cements could be potentially used in high-stress bearing areas.展开更多
Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by the phosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and e...Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by the phosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and effects on CPCs from monocalcium phosphate monohydrate (MCPM) and calcium oxide (CaO) or dicalcium phosphate dihydrate (DCPD) and calcium hydroxide [Ca(OH)(2)] were investigated. Addition of P-chitin (M-w = 2.60 x 10(4); degree of substitution, DS = 0.68) to the liquid phase in amounts up to 3 wt.% for MCPM and CaO cements or 1.5 wt.% for DCPD and Ca(OH)(2) cements could enhance the mechanical strength considerably, while little influence on the setting time was observed. However, further addition of P-chitin will cause no setting.展开更多
The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properti...The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properties such as setting times and strength were tested and the microstructures and pore characteristics of pastes with various bamboos were also studied. The experimental results indicated that bamboo charcoal affects the setting times of cement paste, but the introduction of water reducer relieves this condition. Bamboo charcoal also poses an impact on the hardened paste strength. The prominent strength decrease is found when more and larger size bamboo charcoal is mixed into the cement paste. Bamboo charcoal alters the paste microstructure and increases the porosity and pore volume, but it increases the pores with the diameter of less than 50 μm. The pastes with various bamboo charcoals are given with the good functions such as adjusting humidity and adsorption.展开更多
The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P....The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P.O.42.5,sulphate aluminium) are used in this test. Results show that with the addition of RSF,the setting times for these three kinds of cements are delayed. According to P.O.42.5 cement,The max temperatures of exothermic peak (Tmax) decrease,exothermic peak times (tmax) are delayed and the mechanical strengths generally drop as RSF concentration is increased. XRD test shows that the RSF hinder the formation of Ca(OH)2 phase and hydration of cement (C3S,C2S,C4AF),which resulted in the delay of setting time and hydration reaction.展开更多
基金Funded by Guangxi Science Foundation(No. 0639006)
文摘In order to veritably measure the first peak of hydration heat evolution that has been illustrated important in indicating cement behavior in early hydration, an improved way of water addition into cement in isothermally calorimetric experiment is put forward. The experimental results indicated that: the magnitude of first peak of heat evolution varies from sample to sample, correlation between heat evolution during first peak of heat evolution and initial (as well as final) setting time is unsatisfactory when samples are not classified; while groups of sample classified based on strength grade represent satisfactory correlations, which indicating the existence of close relation between hydration heat evolution in much earlier hydration age and setting property of cement in rather later age. Importance of first peak in hydration heat evolution for understanding cement setting property and reasons for sample classification are also discussed in this paper.
基金Funded by the Major State Basic Research Development Program of China(No.2011CB013800)
文摘Low alkaline liquid state setting accelerator（LSA） for Portland cement was prepared in laboratory from aqueous solution of several inorganic sulfate salts and some organic chemical substances. Properties of cement with addition of LSA relating to its setting time and strength development as well as its resistance to sulfate attack for short and long term exposure were experimentally examined. The experimental results showed that 5%-7% addition of LSA significantly accelerated the initial and final setting of Portland cement in the presence or absence of the blending of mineral admixtures, the initial and final setting time being less than 3 min and 6 min respectively. Meanwhile, the early 1 day curing age compressive strength increased remarkably by 20%, while the late 28 th day curing age compressive strength remained almost unchanged as compared with that of the reference accelerator free cement mortar specimen. Furthermore, mortar specimens of cement added with LSA and exposed to 5% Na2SO4 solution showed their excellent resistance to sulfate attack, with their short and long term curing age resistance coefficient to sulfate attack being around 1.04 to 1.17, all larger than 1.0. XRD analysis on hardened cement paste specimens at very early curing ages of several minutes disclosed the existence of more ettringite in specimens added with LSA than that of the reference specimens, meanwhile SEM observation also revealed the existence of well crystallized ettringite at very early hydration stage, suggesting that the accelerated setting of Portland cement can be attributed to the early and rapid formation of ettringite over the whole cement paste matrix due to the introduction of LSA. MIP measurement revealed that hardened cement paste specimens with the addition of LSA presented less medium diameter pores, more proportion of small pores and less proportion of large capillary pores, which is in a very good coincidence with the improvement of strength development of cement mortars added with LSA.
文摘Microsilica-gel bonded bauxite based no-cement refractory castables（NCCs）have been produced using two readily available dispersants.These NCCs were compared to NCC with Siox X-Zero,a purposely-developed product for microsilica-gel bonded no-cement castable systems to control flow properties and setting characteristics.Three mixing and curing temperatures were applied：5℃,20℃and 35℃.The results show that setting-behaviour and mechanical properties strongly vary with the type of dispersant and the curing temperature.However,both setting and strength are less temperature dependent in the castables with Siox X-Zero.Furthermore,the drying and firing of microsilica-gel bonded NCCs were investigated.Since microsilica-gel bond system contains only a small amount of bound water,the castables can be fired at very high heating rates,once the free water has been removed.
文摘This study contains comparative research of sulfate resistance of ordinary Portland cement pastes with addition of basic aluminum sulfate (hydroxosulfate, Al(OH)1.78(SO4)0.61) and amorphous Al(OH)3. Over 3 months of storing in sodium sulfate solution, the most significant expansion and deterioration occur in case of samples with aluminum hydroxide. During sulfate resistance test, the ratio between aluminum nuclei in AFt (ettringite) and AFm phases was studied by 27Al-MAS NMR, and the impact of aluminum-containing admixtures on this ratio was specified. In accordance with NMR data, in samples with Al(OH)3, the rate of secondary ettringite formation becomes noticeable after one month of storing in sulfate solution. For samples with Al(OH)1.78(SO4)0.61, the rate of elongation and temper of changes in molar ratio between sulfoaluminate phases were comparable with reference samples without admixtures.
文摘The setting chemistry of glass ionomer cement was imestigated by using mechanical determination of compressive strength at predetermined intervals,and measurement of structure changes of correspondling fracture sample by means of IR spectra and differential scanning calorimetry（DSC）.Zinc polycarboxylate cement was used as a comparison sample.The compressive strength of glass ionomer cement（GIC） increases with aging.IR spectra and DSC of corresponding fracture sample show the structure changes of the matrix and interface layer comprising of silica gel during the predetermined intervals studied.however,no significant changes occur in the zinc polycarxyolate cement.Hence the structure changes of the matrix and/or interface layer are responsible for compressive strength increasing with aging.The structure changes include the crosslink density,the ratio of complex form to ionic form,the content ratio of Al-PAA to Ca-PAA,the forming and maturing process of the interface layer comprising of silica gel.
文摘According to the characteristics of granular soil,the technological requirements of the special-purpose cement for stabilizing granular soil are put forward to meet the demands of implementation of highway base engineering.A kind of slow-setting and slight-expansive cement is developed by the cross experiment method in slag-clinker-gypsum-alkaline system,the final setting time of the cement can be prolonged to 8h,and it has properties of low dry shrinkage,high flexural strength and good crack resistance.The strength of granular soil stabilized by the cement is increased by 20% compared with that stabilized by Chinese 425-Grade slag cement.
文摘Brittle fracture of cement sheath, induced by perforation and stimulation treatments, can cause cross flow of formation fluid and increase casing damage. A novel agent XL was developed for solving the problem. Experimental results showed that the toughness of the set cement containing XL was improved remarkably. The engineering properties of the slurry containing XL, drag reducer USZ （0.2% BWOC）, filtrate loss additive F 17B （1.2% BWOC） and crystalloid expanding agent F17A （3% BWOC） could meet technical requirements of cementing operation. After perforation, good quality cement sheath enhanced with XL was observed by CBL/VDL logs in a deep well.
文摘Many measures, such as water injection, acid fracturing, thermal recovery, have been taken in the oilfield development. These can easily induce brittle fracture of set cement. Most of all, there are greater potential for fractures in set cement in slim holes. Therefore, it is necessary to improve the toughness of the cement mantle. Results obtained from experiments show that carbon fiber, with a concentration of 0.12%-0.19% in cement and a length of 700 to 1,400μm, plays an important role in improving cement quality. Addition of carbon fiber can improve the bending strength of set cement by up to 30%. At the same time, the increase in fiber concentration can lower the elastic modulus and increase the Poisson＇s ratio of set cement. Thin-section analysis shows that fiber can effectively prevent the propagation of fractures and enhance the plasticity of the matrix and the ability to prevent fracture.
基金Project supported by the National Major Science and Technology Project“Development of large-scale oil/gas fields and CBM”0“New technologies for improving the cementing quality and wellbore integrity under the condition of large-scale volume fracturing”(No.2016ZX05022-005).
文摘Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development.But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimulation.In this paper,the shale gas development blocks in the Sichuan Basin were taken as the examples to explore the process and support measures that can be used to keep the mechanical integrity of cement sheath under the effect of hydraulic fracturing.It is indicated that the near-bit three-centralizer drifting BHA used for casing stiffness simulation can decrease the casing running difficulty in the long horizontal section of a shale gas well and increase the time efficiency and safety of casing running;that the flushing efficiency of high-efficiency oil flushing spacer fluid system is higher than 90%from room temperature to 120℃,so it can guarantee the displacement efficiency of cement slurry to the oil-based drilling fluid and the effective cementing of borehole wall;that the performance of anti-channeling ductile cement slurry used in the cementing of long horizontal sections in this area after it is set is confirmed,with the elastic modulus of set cement being lower than 7 GPa and triaxial strength being higher than 40 MPa,so as to alleviate or avoid the damage to cement sheath in the process of fracturing;and that cementing quality is improved by applying the support technologies,e.g.drilling fluid adjustment,pre-stress cementing and ground high-pressure pumping.During 2015e2016,these cementing technologies were applied in 85 wells in the Sichuan Basin.The average well depth of these wells is 4832 m,the average length of horizontal sections is 1560 m and the quality rate of well cementing is 89.58%.During the waiting-on-cement(WOC)time after well cementing,there is no sustained casing pressure.And gas channeling in the annulus during well drilling,completion and test is improved remarkably.It is concluded that this suite of technologies can guarantee and improve the cementing quality of long horizontal sections in shale gas wells and provides good cementing conditions for shale gas development.
基金supported by Scientific Research and Technology Development Project of PetroChina Southwest Oil&Gasfield Company“Evaluation method of self-healing slurry”(No.20220302-02).
文摘With the development of cementing slurry technology,cementing self-healing has become one of the most effective technologies to prevent and treat oil and gas channeling and improve long-term sealing capacity of cement sheath.To solve the technical problem of annulus oil and gas channeling caused by the long-term sealing failure of cement sheath,this paper researches and develops a kind of viscosity-soluble type biomimetic self-healing cement slurry system from the perspective of chemical biomimetics,based on the technical idea of“prevention before blocking”.Then,the engineering performance of this biomimetic self-healing cement slurry system and the mechanical property of self-healing set cement are evaluated respectively.In addition,the mechanical recovery capacity and permeability reducing rate of the self-healing set cement conserved with methane are evaluated by creating fractures through splitting.Finally,the healing mechanisms of the self-healing cement are analyzed by means of SEM microscopic test and infrared spectrography.And the following research results are obtained.First,the set cement has excellent mechanical property.When the compressive strength decreases by 15%,the elastic modulus of set cement decreases by 41%,showing good toughness to play the role of“first prevention”.Second,when meeting hydrocarbon,the damaged set cement is excited to generate a kind of viscosity-soluble type gelatinous ester substance,which re-bonds the skeleton of the set cement.When the self-healing set cement is conserved with methane,its compressive strength recovery rate is up to 94.5%,bending strength recovery rate is 58.6%,gas log permeability drops by 99%,and liquid log permeability drops by 100%,so as to realize“blocking later”.In conclusion,the viscosity-soluble type biomimetic self-healing cement slurry system can effectively achieve cementing integrity and long-term sealing integrity through self-healing after the damage of cement sheath,which provides a strong technical support for preventing the production safety hazard of sustained casing pressure in oil and gas wells and is beneficial to solve the technical problem of annulus oil and gas channeling caused by long-term sealing failure of cement sheath.
文摘At present,the mechanical testing on the ductility of cement sheath is faced with multiple technical difficulties.In this paper,numerical simulation and laboratory evaluation were adopted to compare the mechanical performance of typical elastic,flexible,ductile and neat cement systems at home and abroad by different loading rates,value range of stress-strain curve,confining pressure and temperature.It is shown that when the loading rate is lower,the stress-strain curve of set cement is not smooth,but distorted,and the stress cannot be responded in time;that when the loading rate is higher,the stress-strain curve of set cement is smooth,and the yield stage is remarkable,indicating that higher loading rate can reflect the yield strain behavior of set cement more truly;that the recommended Young's modulus range of set cement should be changed based on the actual downhole conditions;that temperature has more effect on yield stress and ultimate strain,but less effect on elastic modulus;that confining pressure has more effect on ultimate stress and ultimate strain,but less effect on elastic modulus;and that when the confining pressure is lower and temperature is higher,the yield stage of set cement is more remarkable.It is concluded that these mechanical behaviors of cement system in different conditions provide a technical support for understanding the mechanical essence of downhole cement sheath and exploring the mechanical integrity of cement sheath and even that of the whole wellbore.
基金Project supported by the National Key Basic Research Program of China(973 Program),“Basic Study on High-efficiency Development of Marine Shale Gas in South China(Part 3“Key Basic Study on Drilling and Completion of Horizontal Shale Gas Wells”)”(Grant No.2013CB228003).
文摘When well cementing is conducted in horizontal shale gas wells in Weiyuan block of the Weiyuan-Changning State Shale Demonstration Area,Sichuan Basin,the oil-based drilling fluid is not compatible with cement slurry,is difficult to be displaced because of its high density,and cement sheath tends to be broken in the situations of large-scale stimulated reservoir volume fracturing.In view of these problems,a series of studies were carried out specifically on the theoretical basis of cement sheath sealing mechanical parameters,oil-displacement preflush improving the interface cementation quality,toughness set cement satisfying large-scale fracturing requirements and cementing technology conducive to the wellbore integrity.The following achievements were made.First,the theoretical model of cement sheath mechanical integrity taking into account the plastic characteristics and interface cementation strength of cement sheath is instructive to the mechanical design of set cement for horizontal shale gas wells,avoiding the micro-annulus as much as possible.Second,oil-displacement preflush is developed and it is well compatible with oil-based drilling fluids and cement slurry with the flushing efficiency on oil-based drilling fluids higher than 90%.Third,the tough set cement which is developed based on the theoretical model of cement sheath sealing integrity not only guarantees higher compressive strength,but decreases Young's modulus by 30%.Forth,it is confirmed that water displacement cementing technology suitable for shale gas wells is conducive to improving the wellbore seal integrity.These research findings were applied in 12 horizontal wells.It is indicated that the quality cementing ratio of horizontal segment reaches 92%and the post fracturing effect is very good,which guarantees the sealing integrity of wellbores and provides a technical support for the highly efficient development of shale gas reservoirs.
基金financial support of the National Natural Science Foundation of China (No. 51474017)the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (No. 2014211B013)
文摘As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.
文摘Grout injection is used for sealing or strengthening the ground in order to prevent water entrance or any failure after excavation.There are many methods of grouting.Permeation grouting is one of the most common types in which the grout material is injected to the pore spaces of the ground.In grouting operations,the grout quality is important to achieve the best results.There are four main characteristics for a grout mixture including bleeding,setting time,strength,and viscosity.In this paper,we try to build some efficient grouting mixtures with different water to cement ratios considering these characteristics.The ingredients of grout mixtures built in this study are cement,water,bentonite,and some chemical additives such as sodium silicate,sodium carbonate,and triethanolamine(TEA).The grout mixtures are prepared for both of the sealing and strengthening purposes for a structural project.Effect of each abovementioned ingredient is profoundly investigated.Since each ingredient may have positive or negative aspect,an optimization of appropriate amount of each ingredient is determined.The optimization is based on 200 grout mixture samples with different percentages of ingredients.Finally,some of these grout mixtures are chosen for the introduced project.It should be mentioned that grouting operations depend on various factors such as pressure of injection,ground structure and grain size of soils.However,quality of a grout can be helpful to make an injection easier and reasonable.For example,during the injection,a wrong estimated setting time can destroy the injected grout by washing the grout or setting early which prevents grouting.This paper tries to show some tests in easy way to achieve a desirable sample of grout.
文摘Regardless of the excellent properties of glass ionomer cements,their poor mechanical properties limit their applications to non-load bearing areas.This study aimed to investigate the effect of incorporated short,chopped and randomly distributed flax fibers（0,0.5,1,2.5,5 and 25 wt%） on setting reaction kinetics,and mechanical and morphological properties of glass ionomer cements.Addition of flax fibers did not significantly affect the setting reaction extent.According to their content,flax fibers increased the compressive（from 148 to 250 MPa） and flexure strength（from 20 to 42 MPa）.They also changed the brittle behavior of glass ionomer cements to a plastic one.They significantly reduced the compressive（from 3 to 1.3 GPa） and flexure modulus（from 19 to 14 GPa）.Accordingly,flax fiber-modified glass ionomer cements could be potentially used in high-stress bearing areas.
基金The project was financially supported by the National Natural Science Foundation of China (No. 20174018).
文摘Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by the phosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and effects on CPCs from monocalcium phosphate monohydrate (MCPM) and calcium oxide (CaO) or dicalcium phosphate dihydrate (DCPD) and calcium hydroxide [Ca(OH)(2)] were investigated. Addition of P-chitin (M-w = 2.60 x 10(4); degree of substitution, DS = 0.68) to the liquid phase in amounts up to 3 wt.% for MCPM and CaO cements or 1.5 wt.% for DCPD and Ca(OH)(2) cements could enhance the mechanical strength considerably, while little influence on the setting time was observed. However, further addition of P-chitin will cause no setting.
基金Funded by the National Natural Science Foundation of China(Nos.51678442,51578412,51478348,and 51508404)the National High-speed Train Union Fund(U1534207)+1 种基金the Key Project of the Shanghai Committee of Science and Technology(No.15DZ1205003)the Fundamental Research Funds for the Central Universities
文摘The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properties such as setting times and strength were tested and the microstructures and pore characteristics of pastes with various bamboos were also studied. The experimental results indicated that bamboo charcoal affects the setting times of cement paste, but the introduction of water reducer relieves this condition. Bamboo charcoal also poses an impact on the hardened paste strength. The prominent strength decrease is found when more and larger size bamboo charcoal is mixed into the cement paste. Bamboo charcoal alters the paste microstructure and increases the porosity and pore volume, but it increases the pores with the diameter of less than 50 μm. The pastes with various bamboo charcoals are given with the good functions such as adjusting humidity and adsorption.
基金supported by"the Fundamental Research Funds for the Central Universities"(No.2010-Ⅳ-057)
文摘The purpose of this research is to study the effects of rice straw fibres (RSF) on the setting time,heat of hydration,hydration products (XRD),mechanical properties for cements. Three types of the cements (P.I.52.5,P.O.42.5,sulphate aluminium) are used in this test. Results show that with the addition of RSF,the setting times for these three kinds of cements are delayed. According to P.O.42.5 cement,The max temperatures of exothermic peak (Tmax) decrease,exothermic peak times (tmax) are delayed and the mechanical strengths generally drop as RSF concentration is increased. XRD test shows that the RSF hinder the formation of Ca(OH)2 phase and hydration of cement (C3S,C2S,C4AF),which resulted in the delay of setting time and hydration reaction.
