Drilling fluids properties

Although numerous mud additives aid in obtaining the desired drilling fluid properties, water-based muds have three basic components water, reactive soHds, and inert soHds. The water forming the continuous phase may be fresh water, seawater, or salt water. The reactive soHds are composed of commercial clays, incorporated hydratable clays and shales from drilled formations, and polymeric materials, which may be suspended or dissolved in the water phase. SoHds, such as barite and hematite, are chemically inactive in most mud systems. Oil and synthetic muds contain, in addition, an organic Hquid as the continuous phase plus water as the discontinuous phase. 

Procedures for determining drilling fluid properties ate available (21,22,166). Tests and test methods ate constantly reviewed by API committees to ensure acceptable accuracy when performed under field conditions as well as in the laboratory. API pubHcations ate tepubUshed as new tests ate added or existing tests ate modified. 

Upon shutting in the well, the pressure builds up both on the drillpipe and casing sides. The rate of pressure buildup and time required for stabilization depend upon formation fluid type, formation properties, initial differential pressure and drilling fluid properties. In Ref. [143] technique is provided for determining the shut-in pressures if the drillpipe pressure is recorded as a function of time. Here we assume that after a relatively short time the conditions are stabilized. At this time we record the shut-in drillpipe pressure (SIDPP) and the shut-in casing pressure (SICP). A small difference between their pressures indicates liquid kick (oil, saltwater) while a large difference is evidence of gas influx. This is true for the same kick size (pit gain). 

Consideration should be given to the inhibitor s effects on drilling fluid properties, other than corrosivity. 

To select a microbiocide one should consider its compatibility with the system. Some chemicals may affect the performance of the drilling fluids and lead to other problems. For example, quats, amines, and chlorinated phenols may cause clay flocculation of the drilling fluid if present in sufficient quantities. Therefore, the effect of the microbiocide on the drilling fluid properties must be thoroughly tested and understood before the chemical is used. 

Contamination can occur while drilling either gas- or water-bearing formations, so it is customary to provide an alkahne buffer to help neutralize them. In most cases the alkaline buffer is used to preserve driUing fluid properties, as well as to reduce corrosion problems. Alkaline materials have limitations and may be insuflicient to neutralize the acid gases if serious contamination is occurring. Under these conditions much of the gas may be vented to the atmosphere from the surface pits or disposed of even more efficiently by degassing equipment In addition, drilling fluid properties can be adjusted to facilitate the escape of the gas. 

Organic inhibitors used to protect drill pipe in weighted, as well as in low-sohds muds are effective when proper attention is given to the application method. Every effort should be made to apply the inhibitor to the drill pipe rather than to mix into the drilling fluids. This permits better control of drilling fluid properties and avoids excessive corrosion inhibitor costs. 

Uses Emulsifier, penetrant, corrosion inhibitor for industrial use lubricant and detergent for drilling fluids Properties Cl. It. vise. Iiq. 36% cone. 

Uses Primary emulsifier, fluid loss control agent for invert muds Features Esp. effective as a component of ester-based syn. drilling fluids Properties Amber vise, liq. sol. in oil insol. in water sp.gr. 0.93-0,99 vise, 8200 eps pour pt. 21 F flash pt. (PMCC) > 212 F Use Level 6-10 Ib/bbI mud Wellguard 4060 [Albemarle]... 

Chem. Descrip. Modified fatty acids ionic Nature Anionic/cationic Uses Emulsifier for oil-based drilling fluids Properties Liq. oil-sol. 

Uses Emulsifier for agric. chemicals wetting agent for oil-based drilling fluids Properties Bm. vise, liq. flash pt. (CC) > 28 C pH 6.5-8.0 (3%) 68.5 1.5% act. Nansa EVM70/E [Huntsman Perf. Prods.]... 

Originally, mud was made from clay mixed with water, a simple system. Today the preparation and treatment of drilling fluid has reached a sophistication which requires specialist knowledge. The reason for this becomes clear if we consider the properties expected. 

How well the drilling fluid fulfills these functions is determined primarily by the response of the well. The whole drilling operation suffers if the fluid is not adequate. In extreme cases, drilling may be stopped or a hole may have to be redfilled. A variety of physical and chemical properties are monitored to ensure satisfactory performance and guide fluid formulation and treatment (21,22). 

Filtration Properties. Drilling fluids have a natural tendency to flow into permeable formations because the borehole pressure is generally... 

Acrylamide polymers are used as multipurpose additives in the oil-producing industry. Introduction of polymers into drilling fluids-drilling muds improves the rheological properties of the fluids in question, positively affects the size of suspended particles, and adds to filterability of well preparation to operation. Another important function is soil structure formation, which imparts additional strength to the well walls. A positive effect is also observed in secondary oil production, where acrylamide polymers additives improve the mobility of aqueous brines injections, which contribute to... 

Dispersed Noninhibited Systems. Drilling fluid systems typically used to drill the upper hole sections are described as dispersed noninhibited systems. They would typically be formulated with freshwater and can often derive many of their properties from dispersed drilled solids or bentonite. They would not normally be weighted to above 12 Ib/gal and the temperature limitation would be in the range of 176-194°F. The flow properties are controlled by a deflocculant, or thinner, and the fluid loss is controlled by the addition of bentonite and low viscosity CMC derivatives. 

The chemical treatment methods reduce dispersability property, of drilling fluids through the increase of size of cuttings which improves separation and prevents the buildup of colloidal solids in the mud. These methods include ionic inhibition, cuttings encapsulation, oil phase inhibition (with oil-base muds), and flocculation. The mechanical solids removal methods are based on the principles presented in Table 4-55. 

Drilling fluid type and properties (density, viscosity, fluid loss, etc., solids content, differential pressure, etc.)... 

Nesbitt, L. E., et al., Properties of hydrogen sulfide scavengers used in water-based drilling fluids, Proceedings of 36th Annual Technical Meeting of the Petroleum Society, Edmonton, Canada, June 2-5, 1985. 

Other uses of thickening agents include pharmaceutical preparations, paper production, and oil well drilling fluids. This latter use is necessary because oil is obtained from rock that is porous. In order to remove the oil without altering the mechanical properties of the porous rock, viscous liquids ( drilling fluids ) are pumped into the rock to replace the oil. Among the substances that can be used for this purpose are thickened aqueous solutions of polymers such as poly(acrylic acid) or poly(acrylonitrile). 

Polyethercyclicpolyols possess enhanced molecular properties and characteristics and permit the preparation of enhanced drilling fluids that inhibit the formation of gas hydrates prevent shale dispersion and reduce the swelling of the formation to enhance wellbore stability, reduce fluid loss, and reduce filter-cake thickness. Drilling muds incorporating the polyethercyclicpolyols are substitutes for oil-based muds in many applications [195-197,1906,1907]. Polyethercyclicpolyols are prepared by thermally condensing a polyol, for example, glycerol to oligomers and cyclic ethers. 

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