- Settore: Oil & gas
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A class of water muds that use partially-hydrolyzed polyacrylamide (PHPA) as a functional additive, either to control wellbore shales or to extend bentonite clay in a low-solids mud. As a shale-control mud, PHPA is believed to seal microfractures and coat shale surfaces with a film that retards dispersion and disintegration. KCl is used as a shale inhibitor in most PHPA mud designs. In low-solids muds, PHPA interacts with minimal concentrations of bentonite to link particles together and improve rheology without increased colloidal solids loading. <br><br>Reference:<br>Clark RK, Scheuerman RF, Raoth H and van Laar H: "Polyacrylamide-Potassium Chloride Mud for Drilling Water Sensitive Shales," Journal of Petroleum Technology 28, no. 6 (June 1976): 719-726. <br>Reference:<br>Fraser LJ: "New Method Accurately Analyzes PHPA's in Muds," Oil & Gas Journal 85, no. 27 (July 6, 1987): 39-42.
Industry:Oil & gas
A class of salts made from neutralization of formic acid with a metal hydroxide or oxide. Three alkali-metal formates are used in drilling, drill-in and completion fluids, (1) sodium formate, HCOO<sup>-</sup>Na<sup>+</sup>, (2) potassium formate, HCOO<sup>-</sup>K<sup>+</sup> and (3) cesium formate, HCOO<sup>-</sup>Cs<sup>+</sup>. Clear solutions of each can reach densities of 1. 32, 1. 58 and 2. 4 g/cm<sup>3</sup>, respectively. They are near neutral pH and meet HSE standards. Most formates can be mixed together over broad ranges of concentration or temperature without solubility or crystallization problems.
Industry:Oil & gas
A class of polymers constructed with the monomer ethylene, H<sub>2</sub>C=CH<sub>2</sub>, with hydrogen replaced by various chemical groups. Among the many vinyl-based polymers and copolymers are acrylates, methacrylates, acrylamides, acrylate-acrylamide (PHPA), vinyl acetate and the various oligomers of ethylene, polyalphaolefins, linear alphaolefins and isomerized olefins. The prefix "vinyl" is more correctly "ethenyl" and sometimes "vinylene. " "Polyvinyl" is synonymous with vinyl polymers, but not specific to an exact polymer. For example, polyvinyl acetate, polyvinyl alcohol, polyvinyl sulfide are commonly used polymers based on ethylene monomers.
Industry:Oil & gas
A class of polymers added to a drilling-grade clay mineral during grinding, or added directly into a clay-based mud system, to enhance the clay's rheological performance. In concept, clay-extender polymers achieve the type of rheology needed for fast drilling with fewer colloidal solids and lower viscosity at high shear rate (at the bit). This is the concept of a "low-solids, nondispersed mud" system. Extenders are usually long-chain anionic or nonionic polymers that link clay platelets together in large networks. Anionic polymers are highly effective but can be precipitated by hardness ions. Nonionic polymers are less effective but also much less sensitive to hardness ions. Excessively long, linear polymers may break up under mechanical shearing. Either by precipitation or breakup, extender polymers can quickly become ineffective if poorly chosen and used improperly. A drilling-grade clay that has no extender is that which meets the standard for API nontreated bentonite. API bentonite and OCMA-grade API bentonite usually contain extender polymers.
Industry:Oil & gas
A class of muds that contain potassium ion (K<sup>+</sup>) dissolved in the water phase. Potassium muds are the most widely accepted water mud system for drilling water-sensitive shales, especially hard, brittle shales. K<sup>+</sup> ions attach to clay surfaces and lend stability to shale exposed to drilling fluids by the bit. The ions also help hold the cuttings together, minimizing dispersion into finer particles. The presence of Na<sup>+</sup> ions counteracts the benefits of K<sup>+</sup> ions and should be minimized by using fresh water (not sea water) for make-up water. With time, Na<sup>+</sup>, Ca<sup>+2</sup> and other ions accumulate from ion exchange with clays, making the mud less effective, but regular treatment to remove Ca<sup>+2</sup> improves polymer function. Potassium chloride, KCl, is the most widely used potassium source. Others are potassium acetate, potassium carbonate, potassium lignite, potassium hydroxide and potassium salt of PHPA. Use of bentonite clay is restricted because of its strong affinity for K<sup>+</sup>. Instead, various polymers are used. XC polymer and PHPA are used for rheology. For fluid-loss control, mixtures of starch and polyanionic cellulose are often used. CM starch, HP starch, carboxymethylcellulose and sodium polyacrylate (SPA) are also used. PHPA is widely used for shale encapsulation. Potassium, lime and starch-like polymers have also been used as potassium mud systems. Although three API methods exist for determining the K<sup>+</sup> ion concentration, the centrifuge method (for K<sup>+</sup> >5000 mg/L) is the most accepted field method, and essential for daily monitoring of potassium in a mud. Regular additions of potassium salt maintain shale stability. K<sup>+</sup> ion is rapidly consumed while drilling shallow, soft and highly dispersive (gumbo) shales, but maintaining sufficient K<sup>+</sup> ion to stabilize gumbo can become expensive when drilling large holes. Researchers, notably Dr. Dennis O'Brien and Dr. Martin Chenevert (while at Exxon Production Research), evaluated different shales, their clay mineralogy and the concentration of K<sup>+</sup> needed to stabilize them. Potassium muds above about 1 wt. % K<sup>+</sup> ion usually fail the mysid shrimp (US EPA) bioassay test. Therefore, K-muds currently find low acceptance in offshore drilling in USA waters. <br><br>Reference:<br>O'Brien DE and Chenevert ME: "Stabilizing Sensitive Shales with Inhibited Potassium-Based Drilling Fluids," Journal of Petroleum Technology 25, no. 9 (September 1973): 1089-1100.
Industry:Oil & gas
A chemical with the formula NaHCO<sub>3</sub>. It is called bicarb at the drilling rig and is used to treat cement contamination in water mud. When cement hydrates, substantial amounts of lime, Ca(OH)<sub>2</sub>, are produced. As the cement sets, less free lime is available. When partially set cement is drilled with a water mud, Ca<sup>+2</sup> and OH<sup>-</sup> ions are leached into the mud, often causing problems associated with clay flocculation and polymer precipitation. Bicarb can be added, either as a pretreatment or over a period of time, to remove the Ca<sup>+2</sup> in the form of insoluble CaCO<sub>3</sub> while simultaneously neutralizing OH<sup>-</sup> ions with the H<sup>+</sup> ion in the bicarb molecule.
Industry:Oil & gas
A chemical with the formula Na<sub>2</sub>CO<sub>3</sub>. It is called soda ash at the drilling rig and is used to treat most types of calcium ion contamination in freshwater and seawater muds. For cement contamination, sodium bicarbonate is used. Calcium ions from drilling gypsum or anhydrite, CaSO<sub>4</sub>, cause clay flocculation and polymer precipitation and lower pH. A soda-ash treatment is appropriate for gypsum contamination because caustic soda, NaOH, is not needed to raise pH. This is also generally the case with hard water influxes into water muds.
Industry:Oil & gas
A chemical with formula CaO, commonly called quick lime or hot lime. When hydrated with one mole of water, it forms slaked lime, Ca(OH)<sub>2</sub>. Quick lime is used in preference to slaked lime at oil mud mixing plants because it generates heat when it becomes slaked with water and therefore speeds up emulsification by the reaction to form calcium fatty-acid soap.
Industry:Oil & gas
A chemical with formula Ca(OH)<sub>2</sub>, commonly called slaked lime. Lime is used in lime muds and as a treatment to remove carbonate ions. It is used as a stabilizing ingredient in oil- and synthetic-base mud, essential to formation of fatty-acid soap emulsifiers. It is an alkaline material that can be carried in excess to neutralize hydrogen sulfide (H<sub>2</sub>S) and carbon dioxide (CO<sub>2</sub>).
Industry:Oil & gas
A chemical used in preparation and maintenance of an oil- or synthetic-base drilling fluid that forms a water-in-oil emulsion (invert emulsion). An oil-mud emulsifier lowers the interfacial tension between oil and water, which allows stable emulsions with small drops to be formed. Historically, oil-mud emulsifiers have been classified as primary and secondary. Secondary emulsifiers are generally not used alone to make a stable oil mud. Emulsifiers can be calcium fatty-acid soaps made from various fatty acids and lime, or derivatives such as amides, amines, amidoamines and imidazolines made by reactions of fatty acids and various ethanolamine compounds. These emulsifiers surround water droplets, like an encapsulating film, with the fatty acid component extending into the oil phase. Emulsifier molecules that cannot fit around drops form clusters (micelles) in the oil phase or adsorb onto solids. Oil-mud emulsion drops each behave like a small osmotic cell. The emulsifier around the drops acts like a semipermeable membrane through which water can move but ions cannot pass. Thus, oil muds have the special capability (which water muds do not have) to control water transfer to and from the drops simply by adjusting salinity within the water phase of the oil mud.
Industry:Oil & gas
