Clays stabilization chemicals

Recent developments have led to the synthesis of a new class of clay-stabilizing chemical additives capable of successfully stabilizing clays in very-low-permeability sandstones, that is, low molecular salts. 

The formation may also contain minerals that are chemically or physically sensitive to the fluid. For that reason clay stabilizing agents, surfactants(5), etc. are also added to the fluids. Fluids that will be produced from the well may contain problem-causing... 

The concentration of treating chemical required for clay stabilization depends on the type and amount of clays involved. Since these chemicals adsorb by cation exchange, a logical approach would be to determine the cation exchange capacity of the formation. The required concentration of treating chemical in the injected solution can then be calculated on basis of the need to completely satisfy the cation exchange capacity in the contacted zone. 

Uses Catalysis thixotropy textile, cosmetic, and grease additive antiperspirant water repellents chemical reagent zirconium salts in lakes and toners of acid and basic dyes oilfield acidizing aid clay stabilizer (oil-well stimulation) thixotropic oil-well cement component... 

Broderick, G.P. and Daniel, D.E. (1990). Stabilizing Compacted Clay against Chemical Attack. J. Geotech. Eng. ASCE, 116(10) 1549. 

As outlined above, surfactants are added to acids to perform one or more of several needed functions. However, other chemicals are also added to the acid. These additives inclnde corrosion inhibitors [IS], iron control agents [J9, 20], hydrogen sulfide scavengers [21], scale inhibitor [22] and clay stabilizers [23], It is very important to perform compatibility tests of the selected surfactant with the acid formnla, especially in this complex environment. Also, some of the snrfactants are nsed in high temperature and high salinity applications. Therefore, it is necessary to ensure thermal stability of these surfactants nnder these harsh conditions. 

As mentioned in the previous sections, surfactants are included in acid formulations to perform specific tasks. In acid stimulation treatments, surfactants encounter various chemical species. First, the surfactant is mixed with the acid and its additives. Some of these additives are cationic, e.g., corrosion inhibitors and clay stabilizers. Others are anionic or nonionic species. Second, the acid reacts with the formation and releases several cations. Hydrochloric acid reacts with carbonate minerals and, as a result, the spent acid contains calcium, magnesium and iron. Hydrofluoric-based acids react with clay minerals and release silicon and aluminum in addition to those dissolved by hydrochloric acid. The presence of these chemicals together with surfactants can cause phase separation of the surfactants. As a result, surfactants will not perform their task as anticipated. 

Chemical Additives The use of chemical additives in sink-float processing is not common except for the use of lime to prevent oxidation and decomposition of the medium. A small amount of clay is sometimes added to improve the kinetic stability of the suspension. 

In these systems, particularly systems such as potassium chloride polymer, the role of bentonite is diminished because the chemical environment is designed to collapse and encapsulate the clays since this reaction is required to stabilize water-sensitive formations. The clay may have a role in the initial formulation of an inhibited fluid to provide the solids to create a filter cake. 

Stresses caused by chemical forces, such as hydration stress, can have a considerable influence on the stability of a wellbore [364]. When the total pressure and the chemical potential of water increase, water is absorbed into the clay platelets, which results either in the platelets moving farther apart (swelling) if they are free to move or in generation of hydrational stress if swelling is constrained [1715]. Hydrational stress results in an increase in pore pressure and a subsequent reduction in effective mud support, which leads to a less stable wellbore condition. 

C. Durand, A. Onaisi, A. Audibert, T. Forsans, and C. Ruffet. Influence of clays on borehole stability A literature survey Pt 1 Occurrence of drilling problems physico-chemical description of clays and of their interaction with fluids. Rev Inst Franc Petrol, 50(2) 187-218, March-April 1995. 

Hall, B.E. "Workover Fluids. Part I - Surfactants have differing chemical properties that should be understood to ensure proper application," World Oil(May 1986) 111-114 ibid "Part 2 - How the various types of surfactants are used to improve well productivity," World Oil(June 1986) 64-67 ibid "Part 3 - Use of alcohols and mutual solvents in oil and gas wells," World Oil(July 1986) 65-67 ibid "Part 4 - Use of Clays and fines stabilizers and treaters," World Oil(October 1986) 61-63 ibid "Part 5 - How certain chemicals react to stabilize clays and fines in the formation," World Oil(December 1986), 49,50. 

Table I. Chemical Structures of Clay and Mineral Fines Stabilizers...

Results indicate that the effectiveness of quaternary ammonium salt polymers in stabilizing swelling clays and mineral fine particles is dependent on monomer chemical structure and polymer molecular weight. Long flexible pendant sidechains containing quaternary nitrogen atoms appear to be required for these polymers to function as mineral fine particle stabilizers. 

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