Synthesis and Performance Evaluation of Multifunctional Drilling Fluid Additive MPA-1

This study presents an idea of developing multifunctional drilling fluid additives to deal with the problems encountered in field drilling fluid engineering, such as too many kinds of drilling fluid additives, drilling fluid additives with their main function being prominent and secondary functions being unsatisfactory, as well as many drilling fluids with complex compositions, difficulties in property maintenance and poor compatibility among the additives. A multifunctional drilling fluid additive MPA-1 with three functions, which are filtration reduction, shale inhibition and lubricity improvement, was developed through L₉(3⁴) orthogonal experiment with which the monomers and their optimal concentrations, and the optimal reaction conditions were determined. The number average molecular weight and the weight average molecular weight of MPA-1 are 15.6×10⁴ and 28.2×10⁴, respectively. TGA results show that the initial decomposition temperature of the MPA-1 molecules is about 255℃. Compared with many other commonly used single-function additives, 1%MPA-1 in a 5% sodium bentonite slurry exhibits better performance in filtration control, lubrication and shale inhibition after the slurry is aged at 120℃ for 16 h. In 5% sodium bentonite slurry containing 5%-10%KCl, MPA-1 exhibits good salt resistance. When three samples of a potassium amine/potassium polymer sulfonate drilling fluid, which was used to drill 3 wells, were treated with 0.3%-0.5%MPA-1 and then allowed to age at 120℃ for 16 h, the viscosity of the samples increased moderately, the API filtration rate decreased significantly, and the lubricity of the mud cakes was improved. Replacing the 1%KPAM+1%Lube-3+1%SMJA-1 in the field potassium amine drilling fluid with 1.5%MPA-1, the composition of the drilling fluid was simplified, and the filtration rate, viscosity, viscosity coefficient of the drilling fluid, as well as the relative rate of expansion of bentonite pallets were wholly reduced. Mechanism analysis shows that the cationic groups in MPA-1 molecules moderately improve the hydrophobicity of clay particles by adsorbing on their surfaces, thereby inhibiting the clay particles and improving the lubricity of the drilling fluid at the same time. The anionic groups in the MPA-1 molecules, on the other hand, enter the hydration layer of clay particles, thereby enhancing the electronegativity of the clay particle surfaces, and increasing the thickness of the hydration films. These effects, together with the encapsulating effect of the main chains of the MPA-1 molecules, enlarge the range of the particle size distribution of the clay particles, which in turn helps produce thinner and denser mud cakes, reducing the filtration rate of the drilling fluid. The results of the research indicate that the multifunctional drilling fluid additive MPA-1 has the ability to reduce filtration rate, enhance lubricity and improve shale inhibition which satisfy the requirements of drilling a well with bottomhole temperatures less than 150℃, and this is beneficial to simplifying mud composition and reducing the difficulties in the maintenance and treatment of a drilling fluid in field operation.