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28BENTONITE CLAYS USED AS THE BASIS OF DRILLING MUDS AND THEIR STRUCTURE-FORMING ABILITIES Kalbaev A.M.1, Abdikamalova A.B.2, Maratov N.Q.3
1Kalbaev AlisherMaqsetbaevich - student, CHEMISTRY-TECHNOLOGICAL FACULTY;
2Abdikamalova Aziza Bahtiyarovna - doctor of philosophy (PhD) in technical Sciences,
Associate Professor, DEPARTMENT OF ORGANIC AND INORGANIC CHEMISTRY;
3Maratov Nursultan Qayratovich - student, CHEMISTRY-TECHNOLOGICAL FACULTY, KARAKALPAK STATE UNIVERSITY, NUKUS, REPUBLIC OF UZBEKISTAN
Abstract: clays are the main structure-forming and crust-forming components of drilling fluids. The most important indicators of clay solutions are the strength of the structure and the effective viscosity, i.e. these characteristics contribute to the solution of the problem of regulating the rheological properties of drilling mud fluids that characterize the physicochemical state of the latter, the level of coagulation and stabilization, the solid phase's solids, its concentration.
Keywords: kaolinite, montmorillonite, palygorskite, hydromica, structure formation, effective viscosity.
It is known that clays are widely used in many branches of industry and national economy and occupy a decisive place in the life of mankind. One of the largest geologists of America said: "The average consumption of clay per person - is an indicator of the height of the culture of the country" [1. 6-7].
Clay is a plastic sedimentary rock, consists mainly of the following minerals: kaolinite, hydromica, montmorillonite, etc. Clay minerals are highly disperse systems, formed mainly in the process of chemical weathering of rocks. High dispersion of clay minerals and their specific properties are achieved due to the peculiarities of their crystal-chemical structure, the ability of basal faces and micro-crystals to interact actively with water molecules [2. 24].
The initial structural elements that provide the construction of all types and varieties of clay minerals are alumino-oxygen-hydroxyl and silica-oxygen layers. In most clay minerals, part of Al can be replaced with Fe, Mg, Zn and other elements [3. 1-3; 4. 74-77].
Clay minerals, depending on the ratio of the amounts of tetrahedral and octahedral nets, are classified according to two main types of lattices. The first type 1: 1 consists of one alumino-oxygen-hydroxyl and one flint-oxygen unit. Another type 2: 1 consists of one alumino-oxygen-hydroxyl unit [2. 25]. Here the method of articulation of structural elements and their number in a unit cell determines the crystalline type of clay minerals.
Clays are the main structure-forming and crust-forming components of drilling fluids. The most important clay minerals of interest for producing drilling mud fluids are montmorillonite, kaolinite, hydromica and palygorskite [5. 59-65].
Kaolinite - in an elementary layer, one two-dimensional grid of silica-oxygen tetraheda is articulated with a grid of cation-hydroxyl octahedra Al4Si4O10(OH)8, (type 1:1), crystallizes in triclinic syngony. Atoms of oxygen and hydroxides of adjacent layers of anions of adjacent packets are opposite each other and have a fairly strong connection [6. 14-15]. Kaolinite is characterized by a regular alternation of layers with a period of about 7 A. X-ray diffractograms present strong reflexes of 7.1 and 3.5 A. Hardness of 1-3, has a density of 2.5-2.7 g / cm3.
Clays of this type have low hydrophilicity, exchange capacity and swelling. Kaolinite is formed during the decomposition of feldspars, which occurs under the influence of weathering processes or when exposed to heated water coming from the depths.
Montmorillonite crystallizes from the monoclinic system of Na(Mg,Al)2(Si4OiQ) (OH)2*4H2O. Hardness 1, has a density of about 2 g / cm3. A characteristic feature of the minerals of this group is the ability of their crystal lattices to expand. The surface of the montmorillonite packets is electronegatively charged, water or other polar liquids can easily penetrate into the inter-pack space and as a result, they swell. When water is removed, the packets are compressed [7. 41-43]. Among the minerals belonging to the group of montmorillonite, several varieties are known.
Hydromica - a structural unit, - is a combination of two outer tetrahedral silicon-oxygen layers and one octahedral, enclosed between them. The vertices of the tetrahedra of the outer silicic acid layers are turned toward its centre and are connected with the octahedral layer by the replacement of hydroxides with hydrogen atoms. In mica, some of the silicon atoms are always replaced by aluminium, resulting in a negative charge, which is balanced by potassium ions located in hexagonal voids. The interplanar distance is approximately 10 A. These minerals weakly swell. The most common illite is Ki_i,5(H^O)i_Q,^l4[Siy_6Ali_ i5O20](OH)4 [11. 48-50, 12. 14-16].
Palygorskite (attapulgite) is an aqueous silicate of aluminium and magnesium, a mineral of the subclass of chain silicates Mg5(Si4Oi0)2(OH)2*(H2O)44H2O. Two chains, oppositely rotated by the vertices of silica-oxygen tetrahedra, are bound by Mg+2 or Al+3 ions. Palygorskite is characterized by the ability to swell in fresh and salt water almost equally. Therefore, it can be a structure-forming component of salt-saturated drilling fluids [8. 67].
In drilling practice, mono-mineral clays are not used to create drilling fluids. However, the study of such systems allows a deeper and more justified approach to the selection of raw materials for the creation of clay drilling fluids with specified properties [9. 11]. In a number of cases, the mono-mineral system of clay-water, especially under the action of electrolytes, does not satisfy this or that technological process. Poly-mineral clay suspensions are more stable in this respect.
The most important indicators of clay solutions are the strength of the structure and the effective viscosity, i.e. these characteristics contribute to the solution of the problem of regulating the rheological properties of drilling mud fluids that characterize the physicochemical state of the latter, the level of coagulation and stabilization, the solid phase's solids, its concentration, which occurs in the fight against thickening caused by electrolyte or temperature aggression [10.3].
The effective viscosity conditionally characterizes the sum of the viscosity and strength resistance to the flow of the drilling fluid and depends on the shear rate and the shear stress. The higher the shear rate, the lower the effective viscosity. At a constant shear rate, the effective viscosity is also constant, i.e. structure-forming and structure-destructive forces are in an equilibrium state. Of all rheological indicators, the effective viscosity most accurately reflects the actual consistency of the solution, but because of the lack of acceptable measurement methods in field practice, it is estimated by the conventional viscosity - the time of the expiration of a certain volume of drilling mud from a standard VBR-2 instrument.
The problems of the stability of disperse systems are one of the most important in modern colloid chemistry and are of great practical importance in many branches of industry. Due to the presence of uncompensated surface energy, highly disperse clay suspensions are thermodynamically no-equilibrium. The dispersity, mineralogical and chemical composition of the dispersed phase, as well as its concentration, the presence of electrolytes and surfactants, temperature and other physicochemical factors, influence the ability of disperse systems to form spatial coagulation structures, exhibit kinetic and sedimentation stability [10. 22].
The study of the conditions of stability and destruction, as well as the development of specific recommendations that make it possible to obtain and use in industry systems with specified physicochemical properties, are one of the most important tasks in the physical chemistry of disperse systems. Significant progress in the study of the phenomenon of the
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structure formation of disperse systems has been achieved by P.A. Rebinder and his school, A.V. Dumansky, B.V. Deryagin, V.D. Ovcharenko, M.P. Volarevich, K.F. Zhigachom, N.N. Kruglitsky and others.
The term structure is understood to mean a spatial grid formed by the bonds of atoms, molecules, ions, micelles, crystalline intergrowths and particles of colloidal dimensions [5. 4-6]. The presence of such interlayers is associated with an important property of coagulation structures - thixotropy. In a structured system, the entire volume of the dispersion medium is held in such a way that, on the whole, the system does not separate into two separate massive phases, as with coalescence and coagulation, but becomes more stable and stable both in time and in relation to external mechanical influences [11. 3-5].
In colloidal chemistry, thixotropy is defined as the ability for an isothermally reversible transition of sol to gel. A.I. Rabinesson, among the main factors of the structure formation of suspensions, notes the swelling of particles in a dispersed phase. The lower the valency of the clay absorbed cation and the greater its hydration, the lower the concentration of suspensions at which a thixotropic thickening occurs.
F.D. Ovcharenko showed the relationship of swelling with the hydrophilicity of clays: swelling depends on the nature of the clay, the dispersion medium and its polarity [6. 43-45]. E.G. Kister the size of the swelling characterizes the liophilicity of clays. Due to its good structure-forming ability, clay suspensions are widely used as drilling fluids for drilling wells for minerals.
The ability of a clay suspension to retain in suspension the fragments of the rock and prevent it from moving along the cracks into the depth of the formation is ensured by its gelatinization when it is at rest due to structure formation. The strength of such a jelly is found by a mechanical test.
In drilling practice, to determine the kinetic stability of drilling fluids, it is common to judge by the values of daily sludge and stability, which, in spite of the type and purpose of the drilling mud, should not exceed 4% and 0.02 g / cm3, respectively.
Stability determines the difference in specific gravity of the lower and upper parts of suspensions:
Cst=Pl - P2. (1.1)
where: pi and p2 are the specific weights of the lower and upper parts of the suspensions, respectively.
The authors of [9. 45-47] propose, determine the stability value as the ratio of the specific gravities of the upper part of the suspensions to the lower part:
Cst=Pl/p2. (1.2)
In this form, in the opinion of the authors, the stability parameter acquires a strict colloidal-chemical character, and can also be determined with much higher accuracy. To quickly assess the stability of the system using the operational parameters, it is proposed (Kc):
As this review shows, the study of the crystal structure of the investigated clay minerals and differences in their structure makes it possible to understand the essence of the processes of structure formation in their aqueous dispersions and interactions between the surface of clay particles and various reagents, and also allows scientifically to substantiate the presence of certain physicochemical properties in these systems. Therefore, it is necessary to consider these issues in detail for clay minerals that are used as a basis for drilling mud fluids.
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