Bentonite mud

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

The bentonite muds include most types of freshwater muds. Bentonite is added to water-base muds to increase viscosity and gel strength, and also to improve... 

Figure 4-111. Suggested range of plastic viscosity and yield point for bentonite muds [29],...

Figure 4-446. Chloride fatigue test—nondispersed bentonite mud, 8.5 pH. (From Ref [194].)...

Cody, R.D. (1976) Growth and early diagenetic changes in artificial gypsum crystals grown within bentonite muds and gels. Geobgbal Society of America, BuUetin 87, 1163-1168. 

Pseudoplastic behoviour under conditions of high shear Xonthon gum As a lubricant for the bentonite muds used to drill oil wells... 

There are numerous bit types and compositions that are applicable to specific types of rock however, commercial diamond or diamond-impregnated bits are usually the preferred bit from a core recovery and quality standpoint. Tungsten carbide core bits can sometimes be used in weak rock or in high-clay-content rocks. A thin bentonite mud is the typical drilling fluid used for coring. Thick mud can clog the small bit ports and is typically avoided. 

Monsanto, until recently, produced high-molecular-weight vinyl acetate-MA materials as part of their Lytron resin series. These materials have been investigated as extenders for bentonite mud and as flocculants for drilling clays (Table The high carboxyl content and water solubility... 

The alkalinity of the fluid is also essential for corrosion control, rheological properties in bentonite mud, and for its reaction with some formation constituents. Water-based drilling mud (Spud Mud) commonly consists of bentonite clay (gel) accounting for around 10% of the mixture, with additives such as barium sulphate (barite), calcium carbonate (chalk) or hematite (e.g., HSL, 2000). In some cases (Natural Bentonite Mud), caustic soda (ca. 1% of the mud mass) is added to water and bentonite (ca. 9% of the mud mass) to stabilize the pH. The pH usually ranges between 9.5 and 10.5, but higher values are not uncommon (e g., Finger and Blankenship, 2010). 

Legrand, C., and Da Costa, F. (1990J. The effects of shearing on the rheological behaviour of thixotropic bentonite muds. Mater. Struct, 23,126-130. 

ALCOHOLS,HIGHERALIPHATIC-SURVEY AND NATURALALCOHOLSMANUFACTURE] (Voll) -for drilling mud bentonites PETROLEUM - DRILLING FLUIDS] (Vol 18)... 

High molecular weight polyacrylamides are used as viscosity builders in freshwater muds (53) or as bentonite extenders. The ionic nature of the polyacrylamide may range from nonionic to anionic (30% hydrolyzed) depending on the situation. Molecular weights ranging from >3 x 10 are used for this purpose. Polymer concentrations of 0.7—2.8 kg/m (0.25—1.0 Ib/bbl) are used depending on the appHcation. 

Hydrating bentonite in fresh water before adding it to the mud greatly increases its efficiency when the makeup water is contaminated with salt and/or hardness. Prehydrated bentonite can be protected from dehydration by flgnosulfonate (70) or sulfomethylated tannin when used in saturated salt water. Salt water clays, such as sepioflte and attapulgite, provide no filtration control and are normally used with suitable filtration control agents. 

In low sohds muds, vinyl acetate—maleic anhydride copolymers were once used to extend or enhance the viscosity of bentonite suspensions (141). This function is largely performed by polyacrylamides. The vinyl acetate—maleic anhydride copolymers can also have a flocculating effect on drill sohds. Concentrations generally are quite low (0.14—0.57 kg/m (0.05—0.2 Ib/bbl)). 

Freshwater Muds—Dispersed Systems. The pH value of low-pH muds may range from 7.0 to 9.5. Low-pH muds include spud muds, bentonite-treated muds, natural muds, phosphate-treated muds, organic thinned muds (red muds, lignite muds, lignosulfate muds), and organic colloid-treated muds. The pH value of high pH muds, such as alkaline tannate-treated mud, is above 9.5. 

Low Solids Muds—Nondispersed Systems. These muds contain less than 3-6% solids by volume, weigh less than 9.5 Ib/gal, and may be fresh or saltwater ba se. The typical low solids systems are flocculent, minimum solids muds, beneficiated clay muds, and low solids polymer muds. Most low solids drilling fluids are composed of water with varying quantities of bentonite and a polymer. The difference among low solids systems lies in the varying actions of different polymers. 

Methylene Blue. Frequently, it is desirable to know the cation exchange capacity of the drilling fluid. To some extent, this value can be correlated to the bentonite content of the mud. 

Seawater muds are composed of bentonite, thinner (lignosulfonate or lignosulfonate and lignite), and an organic filtration control agent. The typical formulation of a seawater mud is 3.5 Ib/bbl of alkali (2 Ib/bbl caustic soda and 1.5 Ib/bbl lime), 8 to 12 Ib/bbl of lignosulfonate, and 2 to 4 Ib/bbl of bentonite to maintain viscosity and filtration. Another approach is to use bentonite/thinner (ligno-sulfonate)/freshwater premix, and mix it with seawater that has been treated for hardness. This technique will be discussed in the saturated saltwater muds section. 

A modified saturated saltwater mud is prepared with bentonite clay by a special technique. First, bentonite is hydrated in freshwater, then treated with lignosulfonate and caustic soda. This premix is then mixed with saltwater (one-part premix to three-part saltwater). The mixture builds up a satisfactory viscosity and develops filtration control. Thinning of the mud is accomplished by saltwater dilutions additional premix is required for viscosity and water loss control. 

For low solids muds with bentonite extenders the API filtration rate is approximately twice that which would be obtained using a conventional clay/ water mud having the same apparent viscosity. 

A biopolymer produced by a particular strain of bacteria is becoming widely used as a substitute for clay in low-solids muds. Since the polymer is attacked readily by bacteria, a bactericide such as paraformaldehyde or a chlorinated phenol also must be used with the biopolymer. The system has more stable properties than the extended bentonite system, because biopolymer exhibits good rheological properties in its own right, and has a better tolerance to salt and calcium. The system can be formulated to include salt, such as potassium chloride. Such a system, however, would then be classed as a nondispersed inhibitive fluid. 

KCl-polymer (potassium chloride-polymer) muds can be classified as low solids-polymer muds or as inhibitive muds, due to their application to drilling in water-sensitive, sloughing shales. The use of polymers and the concentration of potassium chloride provide inhibition of shales and clays for maximum hole stability. The inverted flow properties (high yield point, low plastic viscosity) achieved with polymers and prehydrated bentonite provide good hole cleaning with minimum hole erosion. 

Heavy metals are present in drilled formation solids and in naturally occurring materials used as mud additives. The latter include barite, bentonite, lignite, and mica (sometimes used to stop mud losses downhole). There are background levels of heavy metals in trees that carry through into lignosulfonate made from them. 

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