Background: Despite the fact that a number of traditional shale inhibitors have been utilized widely in drilling operations, the same additive may be unfavorable for different drilling due to environmental protection requirements which limit scales of use. Hence, a series of polyammonium compounds was prepared from dimethylamine, epichlorohydrin, and melamine (DEM).
Methods: To concentrate our efforts, we used both standard and extra methods to investigate the inhibitive properties of a melamine crosslinking agent using mud balls immersion tests, linear expansion measurements, laser particle distribution measurements, thermogravimetric analysis, and scanning electron microscopy.
Results: The anti-swelling rate of DEM-8 reached up to 92.3% when its concentration reached 0.8%. DEM-8 has strong inhibitive capability to bentonite hydration swelling. DEM-8 can affect the bentonite particle size at a large scale. It may adsorb on the surface of clay through hydrogen bonds and electrostatic interaction by an anchoring effect and a hydrophobic effect.
Conclusions: Compared with a blank solution, DEM-8 displays high inhibitive ability against the hydration and swelling of clay. The mud ball is more stable in DEM-8 solution and its swelling degree is very low compared with that of the control test. The inhibition mechanism of DEM-8 to shale can be deduced in that hydrogen bonding, ion exchange, and anchoring effect help to control the hydration and swelling.
Keywords: Melamine; clay; crosslinked polycation; inhibitor; swelling.