Mud Composition

The major components of all drilling mud systems are similar. All of today s mud systems contain emulsifiers, wetting agents, thinners, weighting agents, gelling agents, brine, and small amounts of other substances and chemicals suspended in 

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Entrained gas and air expands under the reduced pressure of the suction stroke, lowering the suction efficiency. Gas in water-base mud may also deteriorate the natural rubber parts used. Gases are usually separated with baffles or by changing mud composition. 

The fluid loss control of aqueous, clay-based drilling mud compositions is enhanced by the addition of a hydrolyzed copolymer of acrylamide and an N-vinylamide [402], The copolymer, which is effective over a broad range of molecular weights, contains at least 5 mole-percent of the N-vinylamide units, which are hydrolyzed to N-vinylamine units. The copolymers can be made from various ratios of N-vinylamide and acrylamide by using common radical-initiated chain growth polymerization techniques. 

V. S. Kotelnikov, S. N. Demochko, V. G. Fil, and I. S. Marchuk. Drilling mud composition—contains carboxymethyl cellulose, acrylic polymer, ferrochrome lignosulphonate, cement and water. Patent SU 1829381-A, 1996. 

J. Plank. Drilling mud composition and process for reducing the filtrate of metal hydroxide mixtures containing drilling mud compositions. Patent WO 9312194, 1993. 

If there are hydrocarbons present in the formation that is being drilled, they will show in the cuttings as oil stains, and in the mud as traces of oil or gas. The gas in the mud is continuously monitored by means of a gas detector. This is often a relatively simple device detecting the total combustible gas content. The detector can be supplemented by a gas chromatograph, which analyses the composition of the gas. 

An alternative type of downhole mud motor is the mud turbine, (multistage axial flow turbine) which directly drives the bit. The tool consists of an upper section containing the turbine blades and lower section with bearings. As mud is pumped through the upper section the blades are turned. Turbines are designed to rotate at higher speed than the displacement motor. The higher rotation speed requires diamond or composite bits. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Water-Based Muds. About 85% of all drilling fluids are water-based systems. The types depend on the composition of the water phase (pH, ionic content, etc), viscosity builders (clays or polymers), and rheological control agents (deflocculants or dispersants (qv)). 

The failure took place in a large water-tube boiler used for generating steam in a chemical plant. The layout of the boiler is shown in Fig. 13.1. At the bottom of the boiler is a cylindrical pressure vessel - the mud drum - which contains water and sediments. At the top of the boiler is the steam drum, which contains water and steam. The two drums are connected by 200 tubes through which the water circulates. The tubes are heated from the outside by the flue gases from a coal-fired furnace. The water in the "hot" tubes moves upwards from the mud drum to the steam drum, and the water in the "cool" tubes moves downwards from the steam drum to the mud drum. A convection circuit is therefore set up where water circulates around the boiler and picks up heat in the process. The water tubes are 10 m long, have an outside diameter of 100 mm and are 5 mm thick in the wall. They are made from a steel of composition Fe-0.18% C, 0.45% Mn, 0.20% Si. The boiler operates with a working pressure of 50 bar and a water temperature of 264°C. 

The word "composites" has a modern ring. But using the high strength of fibres to stiffen and strengthen a cheap matrix material is probably older than the wheel. The Processional Way in ancient Babylon, one of the lesser wonders of the ancient world, was made of bitumen reinforced with plaited straw. Straw and horse hair have been used to reinforce mud bricks (improving their fracture toughness) for at least 5000 years. Paper is a composite so is concrete both were known to the Romans. And almost all natural materials which must bear load - wood, bone, muscle - are composites. 

Testing of Drilling Fluids 652. Composition and Applications 664. Oil-Based Mud Systems 675. Environmental Aspects 682. Typical Calculations in Mud Engineering 687. Solids Control 691. Mud-Related Hole Problems 695. Completion and Workover Fluids 701. 

Drilling Fluids Composition and Applications Water-Base Mud Systems Bentonite Mud... 

Seawater muds are commonly used on offshore locations, which eliminate the necessity of transporting large quantities of freshwater to the drilling location. The other advantage of seawater muds is their inhibition to the hydration and dispersion of clays, because of the salt concentration in seawater. The typical composition of seawater is presented in Table 4-48 most of the hardness of seawater is due to magnesium. 

The water phase of oil-base mud can be freshwater, or various solutions of calcium chloride (CaCl ) or sodium chloride (NaCl). The concentration and composition of the water phase in oil-base mud determines its ability to solve the hydratable shale problem. Oil-base muds containing freshwater are very effective in most water-sensitive shales. The external phase of oil-base mud is oil and does not allow the water to contact the formation the shales are thereby prevented from becoming water wet and dispersing into the mud or caving into the hole. 

A final important class of composite materials is the composite hquids. Composite liquids are highly stmctured fluids based either on particles or droplets in suspension, surfactants, liquid ciystalhne phases, or other macromolecules. A number of composite liquids are essential to the needs of modem industiy and society because they exhibit properties important to special end uses. Examples include lubricants, hydraulic traction fluids, cutting fluids, and oil-drilling muds. Paints, coatings, and adhesives may also be composite liquids. Indeed, composite hquids are valuable in any case where a well-designed liquid state is absolutely essential for proper delivery and action. 

The average composition of seawater is shown in Table 1-3. Seawater muds have sodium chloride concentrations above 10,000 ppm. Most of the hardness in seawater is caused by magnesium. 

An oil-based drilling mud can be viscosified with maleated ethylene-propylene elastomers [919]. The elastomers are ethylene-propylene copolymers or ethylene-propylene-diene terpolymers. The maleated elastomers are far more effective oil mud viscosifiers than the organophilic clays used. On the other hand, specific organophilic clays can provide a drilling fluid composition less sensitive to high temperatures [491]. 

Differential pressure sticking occurs when the drill pipe becomes imbedded in the mud wall cake opposite a permeable zone. The difference between the hydrostatic pressure in the drill pipe and the formation pressure holds the pipe in place, resulting in a sticking pipe. Differential sticking may be prevented, and a stuck drill bit may be freed, using an oil-mud or an oil- or water-based surfactant composition. 

Such a composition reduces friction, permeates drilling mud wall cake, destroys binding wall cake, and reduces differential pressure. Unfortunately, many of such compositions are toxic to marine life. Synthetic PAOs are nontoxic and effective in marine environments when used as lubricants, retum-of-permeabiUty enhancers, or spotting fluid additives for water-based drilling muds. A continuing need exists for other nontoxic additives for water-based drilling muds, which serve as lubricants, retum-of-permeability enhancers, and spotting fluids. 

The ester class also comprises natural oils, such as vegetable oil [75] spent sunflower oil [940,941,992,993] and natural fats, for example, sulfonated flsh fat [161]. In water-based mud systems no harmful foams are formed from partially hydrolyzed glycerides of predominantly unsaturated Ci6 to C24 fatty acids. The partial glycerides can be used at low temperatures and are biodegradable and nontoxic [1280]. A composition for high-temperature applications is available [1818]. It is a mixture of long chain polyesters and polyamides. 

Compositions containing mixtures of metal hydroxides a polysaccharide, partially etherified with hydroxyethyl and hydroxypropyl groups, are used as fluid loss additives for aqueous, clay-mineral-based drilling muds [1437]. 

A polymeric composition for reducing fluid loss in drilling muds and well cement compositions is obtained by the free radical-initiated polymerization of a water-soluble vinyl monomer in an aqueous suspension of lignin, modified lignins, lignite, brown coal, and modified brown coal [705,1847]. The vinyl monomers can be methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinylacetate, methyl vinyl ether, ethyl vinyl ether, N-methylmethacrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, and additional AMPS. In this process a grafting process to the coals by chain transfer may occur. 

Clays or shales have the ability to absorb water, thus causing the instability of wells either because of the swelling of some mineral species or because the supporting pressure is suppressed by modification of the pore pressure. The response of a shale to a water-based fluid depends on its initial water activity and on the composition of the fluid. The behavior of shales can be classified into either deformation mechanisms or transport mechanisms [1765]. Optimization of mud salinity, density, and filter-cake properties is important in achieving optimal shale stability and drilling efficiency with water-based mud. 

A composition for dissolving filter-cake deposits left by drilling mud in wellbores is composed of an aqueous solution of citric acid and potassium chloride, alkali metal formate, acid tetraphosphate, alkaline earth chloride, and alkali metal thiophosphate [1012]. 

Compositions of high-alumina cement containing quartz or glass, calcium carbonate, microsilica, carbon black, iron oxide red mud or screened fly ash, and styrene-butadiene latex have been described [141,1803,1804]. 

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