High-performance shale plugging agent based on chemically modified graphene

• EDA-G is a new plugging agent to plug nanopores of shale formation.
• EDA-G exhibits both high performance as plugging agent and shale inhibitor.
• The addition of EDA-G was far less than other nano materials.
• A simple method was designed to evaluate the plugging capability of nanopores of shale formation.

Ethylenediamine-modified graphene (EDA-G) performed high performance to plug nanopores of shale formation. A simple method was designed to evaluate the plugging capability of EDA-G solution. Compared with inorganic nano-materials, the addition of EDA-G in drilling fluid resulted in the lowest filtration volume in some specific condition. EDA-G was adsorbed in the surface of shale and formed the tight film, which prevented the invasion of water from shale formation. Artificial cores with low permeability were used to measure membrane efficiency by membrane efficiency tester. The time of downstream reaching to equilibrium in 0.4 wt% EDA-G solution was about 120 times than in 4 wt% NaCl solution. Native shale cores with ultralow permeability were used to test membrane efficiency in 0.4 wt% EDA-G solution and 4 wt% NaCl solution. Downstream pressure began to increase after 300 min in 4 wt% NaCl solution and was stable quickly. But downstream pressure did not increase until 3660 min in 0.4 wt% EDA-G solution. EDA-G solution was suitable to plug nanopores of ultralow permeability shale. More importantly, EDA-G solution inhibited the hydration of clay as well. EDA-G solution exhibited high performance as inhibitor at concentration of 0.2 wt% by carbon content. In a study of linear swelling test using bentonite samples, the addition of water, KCl, polyether amino, Chitosan quaternary ammonium salt (HTCC) and EDA-G caused the expansion height of 4.67 mm, 2.47 mm, 2.02 mm, 1.79 mm and 1.79 mm respectively, which corresponded to the reduction rate of 47%, 57%, 62% and 62%. EDA-G solution exhibited both excellently plugging nanopores property and inhibiting hydration of clay capability. And the two performances were most key factors to stabilize shale formation during drilling operation for water drilling fluid.