Biodegradable oligo (poly-L-lysine) as a high-performance hydration inhibitor for shale

Oligo (poly-L-lysine) (OPLL), utilized as a high-performance inhibitor for the hydration of shale, was synthesized with L-lysine as a monomer by the thermal copolymerization method. OPLL was characterized through Fourier-transform ion cyclotron resonance mass spectroscopy (FT-ICR-MS), nuclear magnetic resonance hydrogen spectroscopy (H-1 NMR), Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetry (TG). The inhibition performance of OPLL was evaluated through the combination of montmorillonite (MMT) linear swelling, MMT dispersion and shale dispersion tests, and these results were compared with those for other commonly-used inhibitors in the field. The results demonstrated that OPLL possessed an outstanding inhibition effect on the hydrated dispersion of both MMT-rich and illite-rich shale that was superior to many commonly-used shale inhibitors such as KCl, 2,3-epoxypropyltrimethylammonium chloride (EPTAC) and polyoxypropylenediamine (Jeffamine D230). Along with excellent inhibition capacity, OPLL also possessed good thermal stability and a broad pH adaptability, and therefore, it can perform well under high temperatures up to 180 degrees C and in the pH range of 7 to 10. Based upon a combined use of X-ray diffraction (XRD) and zeta potential techniques, the inhibition mechanism was determined. The excellent performance of OPLL on shale can be attributed to the synergistic effects of the inhibition of the MMT crystalline swelling and the weakening of the diffuse double layer repulsion between clay particles. Additionally, biodegradability tests proved that OPLL is an environmentally friendly shale inhibitor that can be readily biodegraded.