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Remedial cementing requires as much technical, engineering, and operational experience, as primary cementing but is often done when wellbore conditions are unknown or out of control, and when wasted rig time and escalating costs force poor decisions and high risk. Squeeze cementing is a "correction" process that is usually only necessary to correct a problem in the wellbore. Before using a squeeze application, a series of decisions must be made to determine (1) if a problem exists, (2) the magnitude of the problem, (3) if squeeze cementing will correct it, (4) the risk factors present, and (5) if economics will support it. Most squeeze applications are unnecessary because they result from poor primary-cement-job evaluations or job diagnostics. Squeeze cementing is a dehydration process.
Abstract Main factors which are responsible for the corrosion of the cement sheath in wells are determined based on lab tests and field analyses from a literature survey. A description of the chemistry, mineralogy, physical properties of API well cements and their mechanisms of corrosion in the presence of aggressive formation and injection fluids (such as magnesia or sulfate containing brines and CO2) are given. API cement hydration mainly produces Calcium-Silicate-Hydrate (C-S-H) phases, which are responsible for the strength, and portlandite "Ca(OH)2" which is basically a weak point within the cement matrix. Increasing permeability and portlandite content reduce strength and chemical resistance of set cement towards corrosive media. The addition of pozzolanic materials eliminates portlandite and allows lowering the water content in the cement system. Both effects can reduce the permeability and improve the mechanical properties of set cement. Cement specimens were prepared and exposed to CO2 loaded water at 300 °F and 3,000 psi for 6 months. Mechanical properties tests, microscopy, and quantitative CaCO3 analyses revealed significantly less corrosion and negative impacts for an API cement-pozzolan blend compared to a conventional API cement design at same density. Practical and economical concepts for improvements of the cement sheath with respect to cement slurry design, cementing process and the impact of factors such as temperature or cement admixtures are presented to mitigate cement corrosion.
Summary Main factors that are responsible for the corrosion of the cement sheath in wells are determined on the basis of laboratory tests and field analyses from a literature survey. A description of the chemistry, mineralogy, and physical properties of American Petroleum Institute (API) well cements and their mechanisms of corrosion in the presence of aggressive formation and injection fluids [such as magnesium- or sulfate-containing brines and carbon dioxide (CO2)] is given. API cement hydration mainly produces calcium- silicate-hydrate (C-S-H) phases (xCaO·ySiO2·zH2O), which are responsible for the strength, and portlandite [Ca(OH)2], which is basically a weak point within the cement matrix. Increasing the permeability and the portlandite content reduces strength and chemical resistance of set cement toward corrosive media. The addition of pozzolanic materials eliminates portlandite and allows lowering the water content in the cement system. Both effects can reduce the permeability and improve the mechanical properties of set cement. Cement specimens were prepared and exposed to CO2-loaded water at 300°F and 3,000 psi for 6 months. Mechanical-properties tests, microscopy, and quantitative CaCO3 analyses revealed significantly less corrosion and fewer negative impacts for a pozzolan/API cement blend compared with a conventional API cement design at the same density. These findings were related to the effect of the used pozzolans on the formed C-S-H. Practical concepts for improvements of the cement sheath with respect to cement-slurry design, cementing process, and the impact of factors such as temperature or cement admixtures are presented to mitigate cement corrosion.
Micropozzolan spheres, condensed from the vapors of a metallic silicon/ferrosilicon liquid, possess multifunctional applications in oilwell cements. Commonly available and cost-effective, this amorphous substance imparts significant improvements in the physical and mechanical properties of Portland cements. The practical utility of silica fume as an admixture is practical utility of silica fume as an admixture is primarily attributable to its particle size, chemical composition, primarily attributable to its particle size, chemical composition, and reactivity. Composed largely of silicon dioxide (SiO2), silica fume has an average particle diameter of 0.1 pm (100 times finer than cement or fly ash) and yields a surface area on the order of 20 m2/g.
silica fume was added to cements or cement/fly ash mixtures, several beneficial effects were noted: (1) the water consumptive nature of silica fume allows it to function as an extender and a pozzolan substitute for lightweight cements; (2) high water adsorption combined with an increased pozzolanic reactivity promotes enhanced compressive strengths; (3) the purity and solubility of the material makes it suitable for combating strength retrogression in cements at temperatures above 230 deg. F (110 deg. C); (4) permeability and alkali content of the set product we reduced, both desirous properties in a carbon dioxide (CO2) environment. properties in a carbon dioxide (CO2) environment
As a special function admixture for construction concretes, silica fume has been shown to provide such beneficial properties as very high strength, impermeability', high electrical resistivity, superior abrasion endurance, freeze-thaw durability, and sulfate resistance. First used commercially in 1969, silica fume is being used increasingly for oilwell cementing applications.
Silica fume is a waste product generated during the production of silicon/ferrosilicon metals. In the production of silicon/ferrosilicon metals. In the presence of carbon, quartzitic silica is reduced in the presence of carbon, quartzitic silica is reduced in the 2000 deg. C (3600 deg. F temperatures of electric arc furnaces. A portion of the produced silicon reacts with air to form silicon dioxide (SiO2). As the resultant SiO2 fumes cool, they condense into tiny vitreous particles composed primarily of amorphous silica. The condensed silica fume is then processed to remove impurities and control particle size.
Also known in the construction industry as ferrosilicon dust, silica dust, microsilica, amorphous silica, or volatilized silica, the chemical composition of this material varies somewhat depending on its source. A typical analysis shows silica fume to be composed of 91-95% SiO2 0.5-3% Fe2O3, 1-3% mixed alkalis and 12% carton. The surface area of silica fume is generally in the range of 19-21 m2/g. Portland cements and fly ash have specific surface areas ranging from 0.3 to 0.7 m2/g. Even tobacco smoke with a specific surface area of 10 m2/g, has only half the surface area of silica fume.
ABSTRACT This paper comprises a review of the manufacture and chemistry of portland cement, together with some detailed information on the properties of oil-well cements. The sections on the constitution of cement clinker and the products formed during hydration at atmospheric and elevated temperatures are a resume of information from selected up-to-date literature on these subjects. Data are presented showing the manner in which the compressive strengths, heats of hydration, internal surface areas, And non-evaporable water contents of an ASTM Type I cement and a retarded slow-set oil-well cement change when the curing temperature is varied born 77 to 400 F. and curing pressure is varied from atmospheric to 7,500 psi. Under the section on oil-well cements, unretarded and retarded slow-set cements are defined; and some of the materials used for retarders in the latter cements are listed. Gel, pozzolan, and low water-loss cements are discussed and data are given showing the effects of added bentonite on the properties of slurries of an ASTM Type I cement and a retarded slow-set oil-well cement. Contamination of oil-well cement slurries by sodium chloride and various mudtreating chemicals is discussed and data are given showing the effects of sodium chloride on the properties of slurries. EARLY HISTORY The developmentof portland cements started when man began to calcine limestones to produce quick-lime. As a result of efforts to find cements which could be used under water, it was discovered that limes produced from impure limestones yielded mortars which were superior for this use to those produced from the purer limestones. Such discoveries led to the burning of blends of calcareous and argillaceous materials and to the granting of a patent by the government of Great Britain in 1824 to Joseph Aspdin2 for the manufacture of a cement, which he called "portland cement." Aspdin called his product cement because concrete produced from it resembled stone quarried on the Isle of Portland off the cost of England. Gooding and Halstead: in a review of the development of portland cement in England, report that Smeaton, in his book published in 1796, stated: "I did not doubt but to make a cement that would qual the best merchantable portland stone in solidity and durability." Hadley has reviewed the development of portland cement in the United States. Portland cement was first produced in bottle kilns, then in shaft kilns, which were superseded by rotary kilns.ince then attempts have been made to burn it on traveling grates. However, so far this has not gone much beyond the experimental stage. MANUFACTURE OF PORTLANDCEMENT Raw Materials As early as 1836, it was suggested that the hydraulic properties of portland cement resulted from calcium silicates and calcium aluminates produced during the burning process. At first producers selected for their raw materials impure limestones, some-, times called natural "cement rock," which had compositions desired for the finished cements. This method was gradually replaced by the blending of different materials to give the compounds desired