Drilling fluids functions

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). 

Alkalinity Control. Water-base drilling fluids are generaHy maintained at an alkaline pH. Most mud additives require a basic environment to function properly and corrosion is reduced at elevated pH. The primary additive for pH control is sodium hydroxide [1310-73-2] in concentrations from 3 to 14kg/m (1—51b/bbl). 

Surfactants. Surfactants (qv) perform a variety of functions in a drilling fluid. Depending on the type of fluid, a surfactant may be added to emulsify oil in water (o/w) or water in a nonaqueous Hquid (w/o), to water-wet mud soHds or to maintain the soHds in a nonwater-wet state, to defoam muds, or to act as a foaming agent. 

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... 

Zinc compounds such as zinc oxide and basic zinc carbonate are used in some drilling fluids. Their function is to react out swiftly sulfide and bisulfide ions... 

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). 

A crosslinked starch was described as a fluid loss additive for drilling fluids [632,1626]. The additive resists degradation and functions satisfactorily after exposure to temperatures of 250° F for periods of up to 32 hours. To obtain crosslinked starch, a crosslinking agent is reacted with granular starch in an aqueous slurry. The crosslinking reaction is controlled by a Brabender... 

D. G. Peiffer, J. Bock, and J. Elward-Berry. Zwitterionic functionalized polymers as deflocculants in water based drilling fluids. Patent US 5026490,1991. 

C. G. Zhang, M. B. Sun, W. G. Hou, and D. Sun. Study on function mechanism of filtration reducer the influence of fluid loss additive on electrical charge density of filter cake fines. Drilling Fluid Completion Fluid, 12(4) 1-5,1995. 

A great many additives can be used to impart desired properties to the drilling fluid. In general, the deeper and hotter the well, the more chemical additives are needed to obtain the desired fluid properties. These additives can be classified into different types by function. These include ... 

The results (Figure 7), in this case for succinoglycan, are rather surprising. The transition temperature does not always increase or decrease as a function of the salt concentration, but rather, in some brines, a maximum value is reached after which the transition temperature falls with increasing salinity. This is particularly apparent for the two calcium salts, calcium bromide and chloride, both of which are used extensively in heavy brine drilling fluids. 

In drilling fluids, water-soluble polymers can perform many functions, some of which are ... 

They must perform their required functions in a superior manner e.g., completion fluids must balance the formation pressure and, thus, avoid the possible loss of the well due to blow-out. Drilling fluids should minimize the cost of making hole. 

Well-drilling fluids perform a variety of functions such as ... 

Traditionally, the drilling fluid performs four basic functions and these functions are controlled by its chemical composition. 

Hole Cleaning. A major function of the drilling fluid is to clean the wellbore by carrying the drilled rock cuttings to the surface. The... 

There is increasingly a fifth function that must be met, namely, to minimize the environmental impact of the drilling fluid and the drilled... 

A number of rheological models have been used to describe the rheology of drilling fluids (and non-Newtonian fluids in general) (8, 9, 65-67). These models, it is stressed, have been obtained purely empirically by fitting rasa function of y. A Newtonian fluid is characterized by... 

Dynamic Filtration. Dynamic (or cross-flow) filtration is a considerably more complex separation process than static filtration as the rate of filtration is a strong function of the flow of the drilling fluid. A number of studies (see reference 128 and the references cited therein) have demonstrated the various factors that control dynamic filtration rates. 

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