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Well cementing is the process of introducing cement to the annular space between the well-bore and casing or to the annular space between two successive casing strings. [1] Personnel who conduct this job are called "Cementers".
Cement is introduced into the well by means of a cementing head. It helps in pumping cement between the running of the top and bottom plugs.
The most important function of cementing is to achieve zonal isolation. Another purpose of cementing is to achieve a good cement-to-pipe bond. Too low an effective confining pressure may cause the cement to become ductile.
For cement, one thing to note is that there is no correlation between the shear and compressive strength. Another fact to note is that cement strength ranges between 1000 and 1800 psi, and for reservoir pressures > 1000 psi; this means that the pipe cement bond will fail first. This would lead to the development of micro-annuli along the pipe. [2]
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A. 0–6000 ft used when special properties are not required.
B. 0–6000 ft used when conditions require moderate to high sulfate resistance
C. 0–6000 ft used when conditions require high early strength
D. 6000–10000 ft used under moderately high temperatures and pressures
E. 10000–14000 ft used under conditions of high temperatures and pressures
F. 10000–16000 ft used under conditions of extremely high temperatures and pressures
G. 0–8000 ft can be used with accelerators and retarders to cover a wide range of well depths and temperatures.
H. 0–8000 ft can be used with accelerators and retarders to cover a wide range of well depths and temperatures.
J. 12000–16000 ft can be used under conditions of extremely high temperatures and pressures or can be mixed with accelerators and retarders to cover a range of well depth and temperatures.
API cement grades A, B and C correspond to ASTM type I, II and III.
Given the multitude of cement parameters the best and most thorough and practical method of designing a cement blend is through laboratory testing.
The tests should be conducted on a sample that represents the cement to be used on the job site.
There are 8 general categories of additives.
Can be added to shorten the setting time or to accelerate the hardening process.
Calcium chloride, under the right conditions, tends to improve the compressive strength and significantly reduces the thickening and setting time. Used in concentrations of up to 4.0%. The mechanism of this process is debated, but there are four major theories put forward.
Calcium chloride also produces a high amount of heat during hydration. This heat could accelerate the hydration process.
This heat causes the casing to expand and contract as it dissipates. The differing rates of expansion and contraction could result in the casing pulling away from the cement and lead to the formation of micro-annuli. It also has the ability to affect the cement rheology, the compressive strength development, produce shrinkage by 10–15%, increases the permeability with time, and lowers the sulphate resistance.
They work by one of 4 main theories;
Lignosulphonates : Wood pulp derived polymers. Effective in all Portland cements and added in concentrations of 0.1% to 1.5% BWOC. It absorbs into the C-S-H gel and causes a change of morphology to a more impermeable structure.
Hydroxycarboxylic Acids – They have hydroxyl carboxyl groups in their molecular structure. Below 93 °C they can cause over-retardation. They are efficient to a temperature of 150 °C. One acid used in citric acid with an effective concentration of 0.1% to 0.3% BWOC.
Saccharide Compounds : sugars are excellent retarders of Portland cement. Such compounds are not commonly used due to the degree of retardation being very sensitive to variation of concentration. It also depends on the compound's susceptibility to alkaline hydrolysis.
Cellulose Derivatives: Polysaccharides derived from wood or vegetable matter, and are stable to the alkali conditions of the cement slurry.
Organophosphates : Alkylene phosphonic acids.
Reduce slurry density – reduces hydrostatic pressure during cementing. Increases slurry yield – reduces the amount of cement required to produce a given volume.
Water extenders – Allow/facilitate the addition of water to help extend the cement blend/slurry.
Low-density aggregates – Materials with densities less than Portland cement (3.15 g/cm3)
Hollow Glass Microspheres - engineered high strength (unicellular) low density (average true densities as low as 0.3 g/cc for the medium strength versions), non porous hollow glass spheres, usually below 40 μm in average particle size, enable hydraulic cement slurries as low as 8 PpG (960 Kg/m^3)
Gaseous extenders – Nitrogen or air can be used to prepare foam.
Clays – Hydrous aluminum silicates. Most common is bentonite (85% mineral clay smectite). Can be used to obtain a cement of density 11.5 to 15.0 ppg, with concentrations up to 20%. Used with an API ratio of 5.3% water to 1.0% bentonite.
Bentonite – this is added in conjunction with additional water, used for specific weight control but makes poor cement.
Pozzolan – finely ground pumice of fly ash. Pozzolan costs very little, but does not achieve much weight reduction of the slurry.
Diatomaceous earth – also requires additional water to be added. Properties are similar to those of bentonite.
Silica – α quartz and condensed silica fume. α quartz is used to prevent strength retrogression in thermal wells. Silica fume (micro fume) is highly reactive, and is regarded as the most effective pozzolanic material available. The high surface area increases the water demand to get pumpable slurry. Such a mixture can produce a cement slurry as low as 11.0 ppg.
Normal concentration = 15% BWOC but can be as high as 28% BWOC. Can sometimes be used to prevent annular fluid migration.
Expanded Perlite —Used to reduce the weight as water is added with its addition. Without bentonite the perlite separates and floats to the upper part of the slurry. Can be used to achieve a slurry weight as low as 12.0ppg. Bentonite in concentrations of 2–4% is also added to prevent segregation of particles and slurry.
Gilsonite – Used to obtain slurry weights as low as 12.0ppg. In high concentrations, mixing is a problem.
Powdered coal – Can be used to obtain a slurry with a density as low as 11.9ppg, 12.5–25 lbs per sack are usually added.
Uses latex additives to achieve fluid loss. Emulsion polymers are supplied as suspensions of polymer particles. They contain about 50% solids. Such particles can physically plug the pores in the filter cake.
They increase the viscosity of the aqueous phase and decrease the filter cake permeability.
Organic proteins (polypeptides). Not used above temperatures of 93 °C.
Non-ionic synthetic polymers Can lower fluid loss rates from 500 ml/30 min to 20 ml/30 min.
There are also anionic synthetic polymers and cationic polymers.
The addition of materials that can physically bridge fractured or weak zones. E.g. gilsonite and cellophane flakes added in quantities of 0.125–0.500 lbs/sack.
These are cement slurries that upon entering the formation begin to gel and eventually become self-supporting.
Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.
Guar gum, also called guaran, is a galactomannan polysaccharide extracted from guar beans that has thickening and stabilizing properties useful in food, feed, and industrial applications. The guar seeds are mechanically dehusked, hydrated, milled and screened according to application. It is typically produced as a free-flowing, off-white powder.
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table. This technique is typically used to build diaphragm (water-blocking) walls surrounding tunnels and open cuts, and to lay foundations. Slurry walls are used at Superfund sites to contain the waste or contamination and reduce potential future migration of waste constituents, often with other waste treatment methods. Slurry walls are a "well-established" technology but the decision to use slurry walls for a certain project requires geophysical and other engineering studies to develop a plan appropriate for the needs of that specific location. Slurry walls may need to be used in conjunction with other methods to meet project objectives.
Bentonite is an absorbent swelling clay consisting mostly of montmorillonite which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-montmorillonite.
The self-ionization of water (also autoionization of water, and autodissociation of water, or simply dissociation of water) is an ionization reaction in pure water or in an aqueous solution, in which a water molecule, H2O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH−. The hydrogen nucleus, H+, immediately protonates another water molecule to form a hydronium cation, H3O+. It is an example of autoprotolysis, and exemplifies the amphoteric nature of water.
A plasticizer is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture.
A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. It can effuse through porous solids like a gas, overcoming the mass transfer limitations that slow liquid transport through such materials. SCF are superior to gases in their ability to dissolve materials like liquids or solids. Also, near the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned".
Ion chromatography is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including small inorganic anions, large proteins, small nucleotides, and amino acids. However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein.
In geotechnical engineering, drilling fluid, also known as drilling mud, is used to aid the drilling of boreholes into the earth. Used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells.
Protein precipitation is widely used in downstream processing of biological products in order to concentrate proteins and purify them from various contaminants. For example, in the biotechnology industry protein precipitation is used to eliminate contaminants commonly contained in blood. The underlying mechanism of precipitation is to alter the solvation potential of the solvent, more specifically, by lowering the solubility of the solute by addition of a reagent.
In civil engineering, concrete leveling is a procedure that attempts to correct an uneven concrete surface by altering the foundation that the surface sits upon. It is a cheaper alternative to having replacement concrete poured and is commonly performed at small businesses and private homes as well as at factories, warehouses, airports and on roads, highways and other infrastructure.
Tricalcium aluminate Ca3Al2O6, often formulated as 3CaO·Al2O3 to highlight the proportions of the oxides from which it is made, is the most basic of the calcium aluminates. It does not occur in nature, but is an important mineral phase in Portland cement.
Plastic pipe is a tubular section, or hollow cylinder, made of plastic. It is usually, but not necessarily, of circular cross-section, used mainly to convey substances which can flow—liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipes are far stiffer per unit weight than solid members.
Bioseparation of 1,3-propanediol is a biochemical process for production of 1,3-propanediol (PDO). PDO is an organic compound with many commercial applications. Conventionally, PDO is produced from crude oil products such as propylene or ethylene oxide. In recent years, however, companies such as DuPont are investing in the biological production of PDO using renewable feedstocks such as corn.
Squeeze job, or squeeze cementing is a term often used in the oilfield to describe the process of injecting cement slurry into a zone, generally for pressure-isolation purposes.
Concrete is produced in a variety of compositions, finishes and performance characteristics to meet a wide range of needs.
Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damages are caused by the formation of expansive products produced by various chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms. Other damaging processes can also involve calcium leaching by water infiltration and different physical phenomena initiating cracks formation and propagation. All these detrimental processes and damaging agents adversely affects the concrete mechanical strength and its durability.
Concrete has relatively high compressive strength, but significantly lower tensile strength. The compressive strength is typically controlled with the ratio of water to cement when forming the concrete, and tensile strength is increased by additives, typically steel, to create reinforced concrete. In other words we can say concrete is made up of sand, ballast, cement and water.
Calcium nitrite is an inorganic compound with the chemical formula Ca(NO
2)
2. In this compound, as in all nitrites, nitrogen is in a +3 oxidation state. It has many applications such as antifreeze, rust inhibitor of steel and wash heavy oil.