Study On Structure And Properties Of Hyperbranched Polyamines For Shale Gas-water Based Drilling Fluids

In the process of drilling for shale gas,the abundant bentonite in shale is apt to hydration expansion and dispersion when it meets water,which are hidden dangers for the safe and stability of borehole.In recent years,domestic and foreign scholars have developed a series of inhibitors to address these problems with different results.Most of these inhibitors were based on linear polymer to inhibit the hydration expansion and dispersion of bentonite.From the molecular structure to seek a certain degree of innovation,a hyperbranched polymer as inhibitor was developed to explore the relationship between its structure and performance.In this paper,an AB2 monomer was obtained by the Michael addition of ethylenediamine and methyl acrylate,and an amine-terminated hyperbranched polymer shale inhibitor(Hyperbranched-NH2)was synthesized by the polycondensation of AB2 monomers.Taking linear expansion rate as evaluation criterion,the optimal conditions were as follows:the molar ratio of ethylenediamine and methyl acrylate was 1:1,meanwhile polymerization was respectively carried out at 100 ?,120 ? and 140 ? for 2 hours at each temperature.By fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resnance hydrogen spectroscopy(HNMR),it was confirmed that the polymerization process was the nucleophilic substitution of amine and ester.Also,the primary amine and the secondary amide as inhibition groups in Hyperbranched-NH2were confirmed.By time of flight mass spectrometry,we found that the molecular weight of Hyperbranched-NH2 was mainly distributed in the range of 200-1200.Especially,the typical torispherical microstructure of Hyperbranched-NH2 was found by environmental scanning electron microscopy.The performance of Hyperbranched-NH2 was evaluated by linear expansion experiment,rolling dispersion experiment and rheological experiment.In linear expansion experiment,the linear expansion rate of bentonite in 3%Hyperbranched-NH2 aqueous solution were only 3.49%and 11.42%after 2 hours and 16 hours,respectively,which were equivalent to some common inhibitors.In shale rolling dispersion experiment,the shale cuttings recovery rate achieved 60.79%after rolling at 110? for 16 hours.The results of the rheological test showed that the torispherical Hyperbranched-NH2 had little effect on the viscosity of base slurry system and provided a larger space for the addition of other drilling fluid additives.In the interaction mechanism analysis between Hyperbranched-NH2 and bentonite,it showed that the addition of Hyperbranched-NH2 could effectively reduce the hydration film thickness of bentonite particles,and it also could reduce the Zeta potential absolute value of bentonite particles from-40 mV to-12.9 mV.In the FTIR of bentonite treated with Hyperbranched-NH2,it was confirmed that the formation between protonated primary amine functional groups of Hyperbranched-NH2 and bentonite was a stable and ordered hydrogen bond structure.Meanwhile,the results of XRD test showed that Hyperbranched-NH2 could intercalate into the interlayer of bentonite to prevent the infiltration hydration and the layer spacing of bentonite increased from 1.23019 nm to 1.39298 nm.In the particle size analysis,the median particle size of bentonite particles treated with Hyperbranched-NH2 was 8.384 nm,which was 4.018 nm higher than that in the blank base slurry.It indicated that the torispherical microstructure of Hyperbranched-NH2 could bridge bentonite particles which were dispersive in slurry,compared to other inhibitors,the particle size distribution of bentonite particles treated by Hyperbranched-NH2 was more narrow and uniform,indicating that the interaction between bentonite particles and Hyperbranched-NH2 was more uniform and comprehensive.In the flocculation test,Hyperbranched-NH2 also showed good flocculation capacity to bentonite,which was equivalent to some good inhibitors such as SDJA and Ultrahib.Through the optimization,compounding and evaluation of other drilling fluid additives,a drilling fluid system with good performance was established.The system formulation was as follows:4%Bentonite + 0.24%Na2CO3 + 3%Hyperbranched-NH2+ 0.4%FA-367 + 2.5%SPNH + 1.5%SMP-1 + 0.5%Graphite + Barite.The comprehensive tests of drilling fluid showed that the system had excellent inhibitory property,good rheological property,low fluid loss,well lubricity,high temperature resistance and salt tolerance,which showed a good application prospect.