Drilling fluids solids control

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. 

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. 

Synthetic-based muds are mineral oil muds in which the oil phase has been replaced with a synthetic fluid, such as ether, ester, PAO, or linear alkylbenzene, and are available from major mud companies. The mud selection process is based on the mud s technical performance, environmental impact, and financial impact. Synthetic muds are expensive. Two factors influence the direct cost unit or per-barrel cost and mud losses. Synthetic muds are the technical equivalent of oil-based muds when drilling intermediate hole sections. They are technically superior to all water-based systems when drilling reactive shales in directional wells. However, with efficient solids-control equipment, optimized drilling, and good housekeeping practices, the cost of the synthetic mud can be brought to a level comparable with oil-based mud [1308]. 

Any kind of dispersion that was useful in the reservoir may be, or may become, an undesirable dispersion when produced at a well-head. This could include used drilling fluid that has returned to the surface, conventional oil production that occurs in the form of a W/O emulsion, or foam from an enhanced oil-recovery process. These can present some immediate handling, process control, and storage problems. In addition, pipeline and refinery specifications place severe limitations on the water, solids, and salt contents of oil they will accept in order to avoid corrosion, catalyst poisoning, and process-upset problems. For pipeline transportation, an oil must usually contain less than 0.5% basic sediment and water (BS W). 

Solids control for the drilling fluid system An effective way to reduce the volume of drilling fluid waste is the use of solids control. The efficient use of solids control equipment (for example hydrocyclones and centrifuges) in combination with chemical flocculants minimizes the need for makeup water to dilute the fluid system. An enhanced solids control system designed to compliment a specific drilling operation is a very effective waste minimization technique. 

Drilling fluid systems Improved design and operation of drilling fluid systems can also reduce the need for water. Waste minimization opportunities (such as solids control and detailed system monitoring) have been proven effective in reducing the amount of makeup water needed in a drilling operation. 

Solids Control. The circulating drilling fluid is an open system to which solids are added both at the surface (bentonite and barite to control properties) and in the borehole from drilled formations. The drilled cuttings are removed from the drilling fluid on the surface by a... 

The rheological properties of the drilling fluid have a marked influence on the performance of solids control equipment. Froment et al. (163) have pointed out that an increase in the viscosity of the drilling fluid will decrease the flow rate capacity of the shale shaker and will increase the minimum particle size of the solids in the separated stream from a hydrocyclone that is returned to the circulating drilling fluid. For example, Figure 59 shows the particle size distribution of the solids in the under flow from a hydrocyclone. The density and viscosity of the drilling fluid are observed to have a marked effect on the separation characteristics of the hydrocyclone. 

Figure 58. Particle size distribution of API grade barite and drilled solids in typical drilling fluids. The ranges of particle sizes of solids removed by various items of solids control equipment are shown. (Reproduced with permission from reference 163. Copyright 1986 Society of Petroleum Engineers.)...

The combination of physical and chemical measurements previously described has the capability of giving a full description of the performance and composition of the drilling fluid. These measurements form the basis of a process-control approach to drilling fluids and the ability to correct for changes away from the optimal performance of the fluid by controlled additions of chemicals or changes in the solids control procedure. Such an approach should minimize the use of drilling fluid additives and the dilution-disposal of drilling fluids and should reduce the problems of waste disposal. 

Well drilling fluid additives Methyl, ethyl, etc. vinyl United States 3,654,164 1972 Petroleum Solids Control Inc. Ciba-Geigy ... 

Practical control of micro-organisms can be accomphshed if the pH can be maintained above 10, or if the fluid is saturated with a salt such as sodium chloride. However, because of the proliferous nature of micro-organisms in certain drilling fluids, biocides are needed for control. Chlorinated phenols or paraformaldehyde at concentrations up to 5.7 kg/m are used in drilling fluids. These treatments can vary because the solids in drilling fluid usually favor the growth of micro-organisms and tend to reduce biocidal efficiency. 

Polymer requirements are dictated by the specific application. In drilling, the polymers must be shear stable and provide a means of suspending and removing formation cuttings. For use in hydraulic fracturing, the polymeric fluid must also suspend solid proppants, help control fluid loss, reduce friction and provide viscosity for the creation of fracture width. However, after the treatment the polymer containing fluid must be degradable, so that it can be readily returned from the formation and not interfere with oil and gas production. 

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