Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes.This process requi...Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes.This process requires a good understanding of self-weight consolidation behaviors of the tailings slurry within practical stopes,where many factors can have significant effects on the consolidation,including drainage condition and cement addition.In this paper,the prepared tailings slurry with different cement contents(0,4.76wt%,and 6.25wt%)was poured into1.2 m-high columns,which allowed three drainage scenarios(undrained,partial lateral drainage near the bottom part,and full lateral drainage boundaries)to investigate the effects of drainage condition and cement addition on the consolidation behavior of the tailings slurry.The consolidation behavior was analyzed in terms of pore water pressure(PWP),settlement,volume of drainage water,and residual water content.The results indicate that increasing the length of the drainage boundary or cement content aids in PWP dissipation.In addition,constructing an efficient drainage boundary was more favorable to PWP dissipation than increasing cement addition.The final stable PWP on the column floor was not sensitive to cement addition.The final settlement of uncemented tailings slurry was independent of drainage conditions,and that of cemented tailings slurry decreased with the increase in cement addition.Notably,more pore water can drain out from the cemented tailings slurry than the uncemented tailings slurry during consolidation.展开更多
Cementing carbonate reservoirs is generally a difficult task.The so-called thixotropic cement slurry has gained considerable attention in this regard as it can help tofix some notable problems.More precisely,it can ea...Cementing carbonate reservoirs is generally a difficult task.The so-called thixotropic cement slurry has gained considerable attention in this regard as it can help tofix some notable problems.More precisely,it can easilyfill the leakage layer;moreover,its gelling strength can grow rapidly when pumping stops,thereby increasing the resistance to gas channeling,effectively preventing this undesired phenomenon in many cases.High-temperature thixotropic cement slurry systems,however,are still in an early stage of development and additional research is needed to make them a viable option.In the present study,using a self-developed composite high-temperature thixotropic additive as a basis,it is shown that the compressive strength can be adjusted by tuning the proportion of silica sand,the high-temperature retarder,fluid loss additive and dispersant(compatible with the thixotropic additive).According to the tests,the developed high-temperature thixotropic cement slurry system has a 14 d compressive strength of 29.73 MPa at 150°C,and a thickening time of 330 min when the dosage of retarder is 2%.At the same time,the rheological property,water loss,permeability,water separation rate,and settlement stability of the cement slurry system meet the requirements of cementing construction.展开更多
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 press...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.展开更多
The weight loss of cement slurry is the main cause of early annular air channeling and accurate experimental evaluation of the law of loss change is the key to achieve compression stability and prevent this undesired ...The weight loss of cement slurry is the main cause of early annular air channeling and accurate experimental evaluation of the law of loss change is the key to achieve compression stability and prevent this undesired phenomenon.Typically,tests on the pressure loss of cement slurry are carried out for temperature smaller than 120°C,and this condition cannot simulate effectively the situation occurring in high temperature wells.For this reason,in this study a series of experimental tests have been conducted considering a larger range of temperatures,different retarders and fluid loss additives.The results show that with an increase in the temperature,the weight loss curve of cement slurry changes from a“two-stage”to a“three-stage”behavior,and the risk of channeling increases accordingly.On increasing the amount of retarder and fluid loss additive,the transition time of cement slurry displays a non-monotonic behavior(it decreases first and then increases).It is found that the optimized retarder and fluid loss additive dosage are 0.2%and 2.5%,respectively.展开更多
Based on a carbon fiber cement slurry system developed in the previous work, the relationship between the carbon fiber and the performance of the cement slurry was experimentally investigated. Results show that the us...Based on a carbon fiber cement slurry system developed in the previous work, the relationship between the carbon fiber and the performance of the cement slurry was experimentally investigated. Results show that the use of fiber has no effect on the slurry rheological mode, but influences its rheological behavior. When the fiber proportion ranges from 0.12% to 0.19% and the fiber length from 400 to 1,400 μm, the slurry rheological behavior can be improved. Under the normal pressure, the use of fiber can shorten the thickening time of the cement slurry. When the proportion of the constant-length fiber increases, the water loss of the cement slurry decreases first and then increases, and when the fiber length increases (the fiber proportion being kept constant), the water loss shows the same trend. This indicates that there are optimal values for the fiber length and proportion, which vary under the experimental conditions in the following respective ranges: 0.12%-0.37% and 700-1,400 μm .展开更多
Organic rich dark shale of Q Formation can be found in many areas(e.g.,in the North of S Basin).The shale target stratum is easy to hydrate and often undergoes spallation.Therefore,centering the casing in the horizont...Organic rich dark shale of Q Formation can be found in many areas(e.g.,in the North of S Basin).The shale target stratum is easy to hydrate and often undergoes spallation.Therefore,centering the casing in the horizontal section of the irregular borehole is relatively difficult.Similarly,achieving a good cementflushing efficiency under complex borehole conditions is a complex task.Through technologies such as centralizer,efficient preflushing,multi-stageflushing and ductile cement slurry,better performances can be achieved.In this study,it is shown that the cementing rate in the DY2H horizontal section is 97.8%,which is more than 34%higher than that of adjacent wells.This cementing matching technology for sidetracking horizontal wells can be used to improve the cementing quality of continental shale and provides a reference for future applications in thisfield.展开更多
This study aims to investigate the preparation of fine cement slurries by wet-ground using a pneumatic colloid mill. A pneumatic colloid mill was designed and produced. Furthermore,ordinary Portland cement slurries we...This study aims to investigate the preparation of fine cement slurries by wet-ground using a pneumatic colloid mill. A pneumatic colloid mill was designed and produced. Furthermore,ordinary Portland cement slurries were ground using the pneumatic colloid mill. Moreover,the fineness of ground cement slurries was studied. The particle sizes of ground cement slurries with various cumulated percent were all better than those of cement slurries before grinding. When water was used as the dispersant,the best average diameter of cement slurries was obtained by grinding for 10,and 15 min for cement slurries with water / cement ratio of 1∶ 1,and0. 9∶ 1,respectively. When ethanol was used as the dispersant,the particle sizes of all cumulated percent decreased gradually with the increasing grinding time,and the particle sizes of cumulated percent of D97 decreased rapidly with the increasing grinding time. The grinding effect of big particle sizes of cement slurries is better than that of small particle sizes.展开更多
基金financially supported by the Young Scientist Project of the National Key Research and Development Program of China (No.2021YFC2900600)the Beijing Nova Program (No.20220484057)financial support from China Scholarship Council under Grant CSC No.202110300001。
文摘Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes.This process requires a good understanding of self-weight consolidation behaviors of the tailings slurry within practical stopes,where many factors can have significant effects on the consolidation,including drainage condition and cement addition.In this paper,the prepared tailings slurry with different cement contents(0,4.76wt%,and 6.25wt%)was poured into1.2 m-high columns,which allowed three drainage scenarios(undrained,partial lateral drainage near the bottom part,and full lateral drainage boundaries)to investigate the effects of drainage condition and cement addition on the consolidation behavior of the tailings slurry.The consolidation behavior was analyzed in terms of pore water pressure(PWP),settlement,volume of drainage water,and residual water content.The results indicate that increasing the length of the drainage boundary or cement content aids in PWP dissipation.In addition,constructing an efficient drainage boundary was more favorable to PWP dissipation than increasing cement addition.The final stable PWP on the column floor was not sensitive to cement addition.The final settlement of uncemented tailings slurry was independent of drainage conditions,and that of cemented tailings slurry decreased with the increase in cement addition.Notably,more pore water can drain out from the cemented tailings slurry than the uncemented tailings slurry during consolidation.
基金funded by the National Natural Science Foundation of China(51974355).
文摘Cementing carbonate reservoirs is generally a difficult task.The so-called thixotropic cement slurry has gained considerable attention in this regard as it can help tofix some notable problems.More precisely,it can easilyfill the leakage layer;moreover,its gelling strength can grow rapidly when pumping stops,thereby increasing the resistance to gas channeling,effectively preventing this undesired phenomenon in many cases.High-temperature thixotropic cement slurry systems,however,are still in an early stage of development and additional research is needed to make them a viable option.In the present study,using a self-developed composite high-temperature thixotropic additive as a basis,it is shown that the compressive strength can be adjusted by tuning the proportion of silica sand,the high-temperature retarder,fluid loss additive and dispersant(compatible with the thixotropic additive).According to the tests,the developed high-temperature thixotropic cement slurry system has a 14 d compressive strength of 29.73 MPa at 150°C,and a thickening time of 330 min when the dosage of retarder is 2%.At the same time,the rheological property,water loss,permeability,water separation rate,and settlement stability of the cement slurry system meet the requirements of cementing construction.
基金funded by the CNOOC Scientific Research Project“Study of cementing key properties and its matching technology of LD-10 gas field”(Grant No.CCL2019ZJFN1227).
文摘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.
基金The authors gratefully acknowledge the research project from“Research and test on optimization of calculation model for cementing engineering of high temperature and high pressure wells”(Grant No.CQCJ-2020-06).
文摘The weight loss of cement slurry is the main cause of early annular air channeling and accurate experimental evaluation of the law of loss change is the key to achieve compression stability and prevent this undesired phenomenon.Typically,tests on the pressure loss of cement slurry are carried out for temperature smaller than 120°C,and this condition cannot simulate effectively the situation occurring in high temperature wells.For this reason,in this study a series of experimental tests have been conducted considering a larger range of temperatures,different retarders and fluid loss additives.The results show that with an increase in the temperature,the weight loss curve of cement slurry changes from a“two-stage”to a“three-stage”behavior,and the risk of channeling increases accordingly.On increasing the amount of retarder and fluid loss additive,the transition time of cement slurry displays a non-monotonic behavior(it decreases first and then increases).It is found that the optimized retarder and fluid loss additive dosage are 0.2%and 2.5%,respectively.
文摘Based on a carbon fiber cement slurry system developed in the previous work, the relationship between the carbon fiber and the performance of the cement slurry was experimentally investigated. Results show that the use of fiber has no effect on the slurry rheological mode, but influences its rheological behavior. When the fiber proportion ranges from 0.12% to 0.19% and the fiber length from 400 to 1,400 μm, the slurry rheological behavior can be improved. Under the normal pressure, the use of fiber can shorten the thickening time of the cement slurry. When the proportion of the constant-length fiber increases, the water loss of the cement slurry decreases first and then increases, and when the fiber length increases (the fiber proportion being kept constant), the water loss shows the same trend. This indicates that there are optimal values for the fiber length and proportion, which vary under the experimental conditions in the following respective ranges: 0.12%-0.37% and 700-1,400 μm .
基金funded by the CNPC Science and Technology Department Project(2021ZZ10-03)。
文摘Organic rich dark shale of Q Formation can be found in many areas(e.g.,in the North of S Basin).The shale target stratum is easy to hydrate and often undergoes spallation.Therefore,centering the casing in the horizontal section of the irregular borehole is relatively difficult.Similarly,achieving a good cementflushing efficiency under complex borehole conditions is a complex task.Through technologies such as centralizer,efficient preflushing,multi-stageflushing and ductile cement slurry,better performances can be achieved.In this study,it is shown that the cementing rate in the DY2H horizontal section is 97.8%,which is more than 34%higher than that of adjacent wells.This cementing matching technology for sidetracking horizontal wells can be used to improve the cementing quality of continental shale and provides a reference for future applications in thisfield.
基金National Natural Science Foundation of China(No.51272068)Natural Science Foundation of Henan Province,China(No.2010A430010)Foundation of Henan Key Discipline Open Laboratory of Mining Engineering Materials,China(No.M EM12-21)
文摘This study aims to investigate the preparation of fine cement slurries by wet-ground using a pneumatic colloid mill. A pneumatic colloid mill was designed and produced. Furthermore,ordinary Portland cement slurries were ground using the pneumatic colloid mill. Moreover,the fineness of ground cement slurries was studied. The particle sizes of ground cement slurries with various cumulated percent were all better than those of cement slurries before grinding. When water was used as the dispersant,the best average diameter of cement slurries was obtained by grinding for 10,and 15 min for cement slurries with water / cement ratio of 1∶ 1,and0. 9∶ 1,respectively. When ethanol was used as the dispersant,the particle sizes of all cumulated percent decreased gradually with the increasing grinding time,and the particle sizes of cumulated percent of D97 decreased rapidly with the increasing grinding time. The grinding effect of big particle sizes of cement slurries is better than that of small particle sizes.
