DRILLING FLUID (EN: drilling fluid, drilling mud; DE: Spulung, Bohrschlamm, Spulflussigkeit; FR: boue de forage; ES: lodo de sondeo; RU: буровой раствор) is the technological name for the complex multicomponent disperse system of the suspensive, emulsive, and aerated liquids, which are used for the washing of the boreholes during the process of the drilling.
During the circulation within the borehole, the drilling fluid cleans the bottomhole of the drilled-out rock, transports the drilled-out rock from the borehole, and keeps it in the suspended condition during the stopping of the circulation, activates the process for the destruction of the rock by the drilling bit, prevents the crumblings, collapses, and so on, ensures the quality for the unsealing of the productive horizons, provides the lubricating and anti-corrosive action onto the drilling tools, and rotates the bottomhole motors.
Within the practice of the drilling, they use the drilling fluid, which is based on the hydrous (technical water, hydrogels and fluids of the salts, polymeric, polymeric-clayish, and clayish fluids), and on the hydrocarbonaceous (lime-bitumen solution, inverted emulsion) bases. In case of the drilling within the chemogenic depositions, they use the salt-saturated clayish fluids, and hydrogels; in cases of the possible crumblings and collapses of the walls within the borehole, they use the inhibiting fluids; in case of the impact of the high temperatures, they use the heat resistant (or heat-salt resistant) clayish fluids, and the fluids on the hydrocarbonaceous base, which are effective also during the unsealing of the productive horizons, and during the drilling through the terrigenous and chemogenic unstable rocks. In case of the drilling under the conditions, which are characterized by the abnormally high pressures, they use the heavy drilling fluids, while in case of the non-complicated conditions, they use the technical water, polymer clay-free, and polymer-clayish fluids, with the low content of the hard phase.
The effectiveness of the usage of the drilling fluids depends on their properties, to which there belong the density, viscosity, yield of water, static stress of shear, and others. The density of the drilling fluids is measured by the drilling areometer, and amounts to 900-2500 kilograms per cubic metre. The conventional viscosity is determined by the time of the flowing for the required volume of the drilling fluid from the standard funnel (VP-5); the effective viscosity, which is measured by the rotational viscometer, indicates the ratio between the shear stresses within the flow, and the actual gradient of the speed (600 per second on average), and amounts to 1-100 centipoises. The limit for the static stress of shear (the stress, which is required for the destruction of the structure of the fluid, and for the start of the flow of the fluid) is measured by the viscometer within the limits from 0 to 20 pascals. The water yield of the drilling fluids is characterized by the volume of the leachate (from 2 to 10 cubic centimetres), which was separated from the fluid through the standard filtering surface, in case of the difference of the pressure of approximately 100 kilopascals, during 30 minutes. The thickness of the sediment on the filter (of the filtering crust), which is forming itself during the determination of the water yield, varies within the limits of 1-5 millimetres. The content of the solid phase within the drilling fluids characterizes the concentration of the clay (3-15%), and of the heavy material (20-60%).
For the provision of the effectiveness of the drilling (depending on the specific geological-technical conditions), they regulate the properties of the drilling fluids by the changing of the ratio for the content of the dispersed phase, and of the dispersion environment, and by the introduction of the special materials and chemical reagents into these drilling fluids. For the decrease of the water yield, which decreases the hydration, swelling, and loss of the stability of the rocks, they treat the drilling fluids, which are based on the water, with the decreasers of the water yield: carbon-alcaline reagent, condensed sulfite-alcohol vinasse, carboxymethyl cellulose, hydroxyethyl cellulose, modified starch, acrylic polymers (metasom, and others). The regulation of the rheological properties of the drilling fluids, which are providing the decrease of the hydraulic resistances during the circulation of the fluid, the cleaning of the bottomhole of the drilled-out rock, the decrease of the erosion for the walls within the borehole, is achieved by the introduction of the decreasers for the viscosity (the oxidized substituted lignosulfonate, ferrochromium lignosulfonate, nitrolignin, polyphenols, phosphates), and of the structure-formers (bentonite, palygorskite, asbestos, and others). For the prevention of the water-petroleum-gas manifestations in case of the abnormally high layer pressures, they increase the density of the drilling fluids, by the method of the introduction of the special loaders (for example, by chalk up to 1500 kilograms per cubic metre, by barite and hematite up to 2500 kilograms per cubic metre and more), or they decrease the density to 1000 kilograms per cubic metre at the expense of the aeration for the drilling fluids (see the "Aeration" article), or by the addition of the foam-forming substances (sulfonol, lignosulfonate) into the drilling fluid. The suppression of the hydration and swelling of the rocks, during their interaction with the filtrate from the drilling fluids, is achieved by the treatment of the drilling fluids with the calcium oxide, gypsum, calcium chloride, potassium chloride, sodium hydroxide, potassium hydroxide, liquid glass, and others. They increase the antifriction properties of the drilling fluids by the introduction of the lubricating additives (petroleum, graphite, oxidized petrolatum, mixture of the tars, and others). For the preservation of the rheological and filtrating properties of the drilling fluids in case of the high temperatures, they use the chromates and dichromates of potassium or sodium, and the antioxidants. As the foam extinguishers for the drilling fluids, they use the rubber and polyethylene crumbs, fatty acids and alcohols, siliceous-organical compounds (silicones), and so on. For the regulation of the content of the solid phase, they introduce the selective flocculants into the fluid.
In case of the regulation of the properties of the solutions on the base of the hydrocarbons, they use the peculiar class of the reagents. There belong to them the emulsifiers (the soaps of the fatty acids, emultal, and others), which are introduced into the fluid, in order to provide it with the aggregative stability, the structure forming stabilizers (oxidized petrolatum and bitumen, organic clay), the water repellents (sulphonol, quaternary amines, organosilicon compounds), the decreasers of the filtration (organic humic acids).
They prepare the drilling fluids immediately prior to the drilling, and during the process of the drilling, with the help of the hydraulic mixers and dispersants (see the "Drilling dispersant" article). The content of the hard phase within the drilling fluids is regulated by the 3-stage system for the cleaning, namely, by the vibrating sieves, by the sand separator and silt separator; they separate the gaseous agents within the degassers (see the "Drilling degasser" article). Within the USSR, the annual usage of the drilling fluids, for example, for the drilling for the petroleum and gas boreholes, reaches 50 million cubic metres.
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