To maintain tight control over rheological properties of high-density water-based drilling fluids, it is essential to understand the factors influencing the rheology of water-based drilling fluids. This paper examines...To maintain tight control over rheological properties of high-density water-based drilling fluids, it is essential to understand the factors influencing the rheology of water-based drilling fluids. This paper examines temperature effects on the rheological properties of two types of high-density water-based drilling fluids (fresh water-based and brine-based) under high temperature and high pressure (HTHP) with a Fann 50SL rheometer. On the basis of the water-based drilling fluid systems formulated in laboratory, this paper mainly describes the influences of different types and concentration of clay, the content of a colloid stabilizer named GHJ-1 and fluid density on the rheological parameters such as viscosity and shear stress. In addition, the effects of aging temperature and aging time of the drilling fluid on these parameters were also examined. Clay content and proportions for different densities of brine-based fluids were recommended to effectively regulate the rheological properties. Four rheological models, the Bingham, power law, Casson and H-B models, were employed to fit the rheological parameters. It turns out that the H-B model was the best one to describe the rheological properties of the high-density drilling fluid under HTHP conditions and power law model produced the worst fit. In addition, a new mathematical model that describes the apparent viscosity as a function of temperature and pressure was established and has been applied on site.展开更多
A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential meth...A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential method.All types of pores are simultaneously introduced to the composite during the differential iteration process according to the ratio of their volume fractions.Based on this model,the effects of pore structures on predicted pore-pressure in carbonates were analyzed.Calculation results indicate that cracks with low pore aspect ratios lead to pore-pressure overestimation which results in lost circulation and reservoir damage.However,moldic pores and vugs with high pore aspect ratios lead to pore-pressure underestimation which results in well kick and even blowout.The pore-pressure deviation due to cracks and moldic pores increases with an increase in porosity.For carbonates with complex pore structures,adopting conventional pore-pressure prediction methods and casing program designs will expose the well drilling engineering to high uncertainties.Velocity prediction models considering the influence of pore structure need to be built to improve the reliability and accuracy of pore-pressure prediction in carbonates.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 (C 3 S and C 2 S) 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To maintain tight control over rheological properties of high-density water-based drilling fluids, it is essential to understand the factors influencing the rheology of water-based drilling fluids. This paper examines temperature effects on the rheological properties of two types of high-density water-based drilling fluids (fresh water-based and brine-based) under high temperature and high pressure (HTHP) with a Fann 50SL rheometer. On the basis of the water-based drilling fluid systems formulated in laboratory, this paper mainly describes the influences of different types and concentration of clay, the content of a colloid stabilizer named GHJ-1 and fluid density on the rheological parameters such as viscosity and shear stress. In addition, the effects of aging temperature and aging time of the drilling fluid on these parameters were also examined. Clay content and proportions for different densities of brine-based fluids were recommended to effectively regulate the rheological properties. Four rheological models, the Bingham, power law, Casson and H-B models, were employed to fit the rheological parameters. It turns out that the H-B model was the best one to describe the rheological properties of the high-density drilling fluid under HTHP conditions and power law model produced the worst fit. In addition, a new mathematical model that describes the apparent viscosity as a function of temperature and pressure was established and has been applied on site.
基金the financial support from the National Natural Science Foundation of China (No. 51274230)the Natural Science Foundation of Shandong Province (No. ZR2012EEL01)the Fundamental Research Funds for the Central Universities (No. 14CX02040A and No. 14CX06023A)
文摘A calculation model based on effective medium theory has been developed for predicting elastic properties of dry carbonates with complex pore structures by integrating the Kuster-Toksǒz model with a differential method.All types of pores are simultaneously introduced to the composite during the differential iteration process according to the ratio of their volume fractions.Based on this model,the effects of pore structures on predicted pore-pressure in carbonates were analyzed.Calculation results indicate that cracks with low pore aspect ratios lead to pore-pressure overestimation which results in lost circulation and reservoir damage.However,moldic pores and vugs with high pore aspect ratios lead to pore-pressure underestimation which results in well kick and even blowout.The pore-pressure deviation due to cracks and moldic pores increases with an increase in porosity.For carbonates with complex pore structures,adopting conventional pore-pressure prediction methods and casing program designs will expose the well drilling engineering to high uncertainties.Velocity prediction models considering the influence of pore structure need to be built to improve the reliability and accuracy of pore-pressure prediction in carbonates.
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 (C 3 S and C 2 S) 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.
