Synthesis And Application Of Comb-like Polymer As Dispersant Of Superfine Barite Thick Slurry

Nowadays, the petroleum in the middle-shallow strata has basically been used up, so the exploitation of oilfield is turned to deep strata, bathypelagic zones and other areas with harsh environment. Thus higher requirements have been raised on the research of high-density drilling fluid. It is difficult to control the contradiction between rheology and sedimentary stability in field of high-density drilling fluid. The use of traditional API barite will make it hard to control the rheology property, and lead to sedimentation of solid phase as well.However, electrolyte pollution is unavoidable due to the existence of evaporite bed during oil drilling. So it is urgent to develop a new dispersant with excellent dispersion ability and salt tolerance (NaCl content over 30%). In this thesis, we prepared comb-like polymer dispersants with long side chains via solution radical copolymerization, and polymer-coated superfine barite thick slurry can be obtained by wet-milling the API barite using planetary ball mill.This article includes three aspects:1. Preparation and characterization of comb-like copolymerComb-like polymer dispersants were prepared via solution radical polymerization with macromers (TPEO or APEO) and monomer (AA and AMPS). The Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) show the presence of functional groups in monomers, confirming the comb-like structure. The proportion of each element in the polymer is determined by element analysis so that the ratios of each structural unit can be obtained. The average molecular weight of the comb-like polymers is determined to be 10,000-20,000 by molecular gel chromatograph.2. Preparation and performance test of superfine barite thick slurryIn this thesis, we prepared polymer-coated superfine barite thick slurry with a solid content of up to 80% (density of 2.5g/cm3) by wet-milling the API barite using planetary ball mill. The optical microscope indicates the average size of the particles is less than 2μm. By comparing the rheology property between our thick slurry and that using traditional barite linear dispersants, the superior dispersion ability and salt tolerance of the comb-like polymer dispersants are confirmed. The highest density of superfine barite thick slurry of M-I company is 2.2 g/cm3 and the apparent viscosity is 100 mPa.s. However, the production prepared in this thesis has density of 2.5 g/cm3 and better apparent viscosity of 35 mPa.s. In addition, we provide the method of predicting the stability of barite thick slurry using rheometer, as well as the theory that helps to use superfine barite in a better way in the field of high-density water-based drilling fluid.3. Interactions between comb-like copolymer and bariteIn this thesis, we studied the influence of comb-like copolymers with different side chain densities and lengths to the barite dispersion system by characterization including adsorption, zeta potential and rheology. The polymers adsorb on the surface of barite by forming coordination bonds between carboxyl and sulfonic groups on the polymers and Ba2+ on the barite, meanwhile the side chains stretch outward to the solution. With the increase of polymer concentration, the adsorbance of polymer on the barite increases, and the absolute value of zeta potential of the particles increases accordingly. By comparing the results of rheology property, we found that the increase of side chain length contributed little to the increase of the absolute value of zeta potential. Moreover, longer side chains can lower the viscosity and structural strength of the dispersion system. Thus comb-like copolymers show good dispersion property upon barite system.