In underground diaphragm wall and pile foundation engineering operations,calcium ions from the concrete continually invade into the drilling fluids because of the frequent contact of the drilling fluids with the concrete,leading to gradual deterioration of the basic properties of the drilling fluids and large amount of waste muds after the operations.To improve the calcium resistance of the drilling fluids and minimize the amount of waste drilling fluids produced,the natural bentonite used to formulate the drilling fluids needs to be modified.A calcium-resistant compound bentonite ACB-16 is synthesized with natural bentonite purified through high-speed centrifuging and monomers for polymerization,such as a hydrophilic monomer BX with double carbon bonds,hydrophilic monomers AS and AP with sulfonic acid groups.In the polymerization reaction,the monomers enter into the crystal spaces of the purified bentonite,reacting with each other through in-situ free radical polymerization.Studies on the polymerization products with FT-IR,particle size distribution test,SEM and TEM show that the monomers successfully in-situ polymerize in the crystal spaces of the bentonite.The quality of ACB-16 exceeds the quality of the OCMA bentonite.A drilling fluid formulated with ACB-16 has an apparent viscosity of 26 mPa∙s,an API filter loss of 7.6 mL,a good rheology and filtration property as well as a good calcium resistance.When contaminated with 1%calcium chloride,the rheology and filtration property of the drilling fluid are still stable.The limit of calcium resistance of a drilling fluid formulated with ACB-16 is 6,300 mg/L(equivalent to 1.75%CaCl2),perfectly satisfying the requirements for a drilling fluid to resist calcium contamination in foundation engineering.Using particle size analysis and SEM,the working mechanism of ACB-16 is studied.The high molecular weight polymers located on the networking structures of the bentonite hinder the ion exchange between the calcium ions and the bentonite,thereby maintaining the thickness of the hydration membrane and the c-spacing of the bentonite and supporting the network structures generated by the hydrated bentonite.Direct mixing of ACB-16 with water can obtain a calcium-resistant drilling fluid with excellent properties.ACB-16 is easy to use,it will have good application prospects in foundation engineering and other fields,and it can also be used in formulating anti-sloughing drilling fluids for high calcium environment such as salt and gypsum drilling.
关键词
钻井液/抗钙/膨润土改性/自由基原位聚合反应
Key words
Drilling fluid/Calcium resistance/Modification o bentonite/Free radical in-situ polymerization reaction
维普
万方数据