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Jul 17, 2013 Water is the most important basic material for producing drilling fluids and can form the base for a suitable drilling fluid with solids content whose properties can be adapted to the application conditions or tasks in accordance with Table 37. Thus, fluid admixtures can be created using so-called structure formers (solids structure formers such as bentonite and fluid structure formers such as polymers) and additives such as inert solids or organic … |
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Jul 17, 2013 |
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Jul 17, 2013 Bentonite is one of the most important solid structure formers in connection with drilling fluids. The naturally occurring swelling clay was first discovered in Fort Benton in Wyoming, USA in 1898. The main component of bentonite is the clay mineral Montmorillonite, a layered aluminium hydrosilicate that greatly determines the physical and chemical properties of bentonite [HDD-209] [HDD-210] [HDD-211]. Deposits of bentonite are spread throughout the … |
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Jul 17, 2013 (Image: Filtration of drilling fluid by bentonite platelets entering the pores of the borehole wall)Stability is a suspension’s property not to separate further or to separate very little over time (Figure 150 a). If the components separate themselves, it is referred to as an unstable suspension. Stable suspensions do not separate by themselves but the components of the suspension can be separated by mechanical and/or chemical agents (see (Preparation … |
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Jul 17, 2013 The density ( is a physical parameter and is defined as the relation of the mass m in a substance to its volume V. In this application case, together with the viscosity and the flow velocity, it determines the possible transport capacity of the drilling fluid (cf. (Flow velocity and transport capacity)). It is determined with the aid of a specially configured scale (fluid density scale) or by weighing a known volume. According to this latter method, … |
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Jul 17, 2013 DIN 1342-1 [HDD-218] defines viscosity as the property of a substance (primary terminology for gases, fluids and solids) to flow under the effects of a stress and to be irreversibly deformed. In this process, the flow energy is converted to heat. In the case at hand, in a simplified way viscosity η, measured in [mPa • s], is understood to be the resistance of fluids to relative motion. According to DIN 1342-2 [HDD-218], it is characterised as the … |
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Jul 17, 2013 The yield point τF of a material is understood as its property of being able to take up shear stress τ up to a maximum value without plastic deformation (flow) occurring. For an ideal plastic material or an ideal plastic fluid applies [HDD-204]: a) for τ < τF no plastic deformation The yield point τF according to DIN 4127 [HDD-219], is the shear stress at which flow takes place. It depends on the … |
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Jul 17, 2013 (Image: Shearometer experiment to test gel strength)Gel strength (short: GS, measured in g/cm2) is referred to as the stability of the lattice structures of the structure forming agents. It is a quantity for defining the thrixotropic behaviour of a suspension and grows over time by thixotropic hardening. It also tends to increase with the concentration of bentonite or clay [HDD-14]. Directly after completing intensive stirring, if that destroyed the … |
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Jul 17, 2013 Sand is usually understood to be all solids > 63 μm (Germany) or 74 μm (USA) contained in a drilling fluid irrespective of the mineralogical composition. Also solids < 63 μm or 74 μm act in an eroding and fluidharming way, so that possibly also the concentration of this particle size range has to be determined [HDD-14]. The above mentioned 74 μm or 74 Microns corresponds to a 200 Mesh, which represent the smallest mesh width of the screen panels in … |
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Jul 17, 2013 Bentonite suspensions are used in coarse particle, loose to densely stratified sands or gravels, uneven and inhomogeneous soils with water permeability coefficients of k > 10-3 m/s [HDD-198] [HDD-237]. Pure Bentonite suspensions find their limits of application, on the one hand, in coarse particle soils with open structures such as even shaped coarse gravels and, on the other hand, in pure clay soils. In the latter, because of the absence of inhibiting … |
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Jul 17, 2013 Bentonite is one of the most important solid structure formers in connection with drilling fluids. The naturally occurring swelling clay was first discovered in Fort Benton in Wyoming, USA in 1898. The main component of bentonite is the clay mineral Montmorillonite, a layered aluminium hydrosilicate that greatly determines the physical and chemical properties of bentonite [HDD-209] [HDD-210] [HDD-211]. Deposits of bentonite are spread throughout the … |
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Jul 17, 2013 Polymer drilling fluids are solid-free fluids, in which so-called “fluid structure formers” are added to the water in the form of strongly hydrophilic polymers. Polymers are chemical compounds in which numerous basic molecules of the same or similar type are tightly bound to each other. They are created by an ordered linking of single molecules (monomers) into a chain or macro-molecule (polymerisation). The most important type of linkage is the carbon-… |
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Jul 17, 2013 Bentonite-Polymer drilling fluids consist of water as the base medium to which bentonite and polymers are added. They are preferred in coarse particle soils with open structures, such as even coarse gravels, to prevent the loss of the drilling fluid into the subsoil. They possess a friction-reducing and viscosity-enhancing effect by means of which an improvement of boring is achieved and lower flow velocities for the directional drilling, among others, … |
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Jul 17, 2013 Reduction of filtrate in drilling fluid is understood to be the reduction of the fluid quantity filtering into the subsoil - the reduction of filtrate being due to the formation of a very thin, dense ductile and elastic sealing filter cake (see (Stability)) [HDD-14]. In order to achieve this reduction of filtrate, so-called filtrate reducers based on polymers are used. They consist of macromolecules that are sheathed with a fixed adhesive hydrate … |
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Jul 17, 2013 (Image: Model sketch of the protection of clay particles through polymer sheathing against salts by means of which protective colloidial effect is achieved)The polymer molecules of the filtrate reducers that are intensively adsorbed at the clay particles further form a protection against the coagulating influence of the salt ions (Na+, K+, Ca++, Mg++) at the clay surface. In this function, they act as so-called protective colloids or inhibitors as … |
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Jul 17, 2013 The regulation of viscosity in HDD essentially means a reduction of the viscosity. This is primarily necessary when the drilling fluid begins to thicken due to the absorption of fine solids from the spoil or an increase in alkalinity from the groundwater (e.g. drilling fluids thickened by clay spoil). The simplest method for reducing the viscosity of the drilling fluid is to add water. If the increased viscosity is not intended to or cannot be reduced … |
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Jul 17, 2013 In drilling technology, the flocculation or coagulating of clay particles (clay mud or bentonite) is known as an undesired phenomenon when, for instance, drilling through formations containing electrolytes such as salt with an unprotected bentonite suspension without inhibitors. In the presence of electrolytes usually the repulsive potential between the clay particles is disturbed, so the attractive potential dominates and they ball together into … |
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Jul 17, 2013 Bentonite-Polymer drilling fluids consist of water as the base medium to which bentonite and polymers are added. They are preferred in coarse particle soils with open structures, such as even coarse gravels, to prevent the loss of the drilling fluid into the subsoil. They possess a friction-reducing and viscosity-enhancing effect by means of which an improvement of boring is achieved and lower flow velocities for the directional drilling, among others, … |
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Jul 17, 2013 In the following, the demands, properties and application areas of water-based fluids with or without solids, which are used in HDD, as well as the additives used for an aimed influence of certain fluid properties will be presented. When choosing the drilling fluid for the respective case of application, the geological and hydrogeological conditions described in the geotechnical report (see (Geotechnical investigations) and Volume 1, Section 4.5 [… |
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Jul 17, 2013 Chemically active as well as chemically inactive (inert) additives can be added for targeted influencing of the drilling fluid or of the water as the fluid’s base. According to DIN V 4126-100 [HDD-222], chemically active additives also called mixing media, are added to the drilling fluid with the aim of changing its mechanical properties, especially their flow, penetration and stabilising behaviour. Among the additives are filtrate reducers (see (… |
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Jul 17, 2013 Inert solids are referred to as chemically inert substances. They do not participate, or only partly, in the chemical processes in the drilling fluid and are grouped according to their origin, as well as their utility, into:
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Jul 17, 2013 Lost circulation material is used for tackling drilling fluid loss so that its quantity, sizes and the form of its particles can close the pore space, cracks and fissures, through which the used drilling fluid is led off (Figure 136). So the fluid circuit is recovered or maintained. (Image: Loss of drilling fluid – flowing through the borehole walls, e.g. in soil with large open structures or rock with fissures) The shape and size or the distribution … |
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Jul 17, 2013 Ballasting substances are used for increasing the density and thus the static pressure of drilling fluid especially with the occurrence of water under artesian pressure. They can be used together with polymers. Here care must be taken of the fact that these substances – added individually or in combination – do not influence the primary properties of the drilling fluid in a negative way [HDD-14] [HDD-35]. The following points are decisive in their … |
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Jul 17, 2013 Inert solids are referred to as chemically inert substances. They do not participate, or only partly, in the chemical processes in the drilling fluid and are grouped according to their origin, as well as their utility, into:
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Jul 17, 2013 In contrast to inert additives, there are other, chemically active additives that can be added to drilling fluids. With them, the following aims can be achieved [HDD-14] [HDD-35]:
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