Maintaining shale stability using polyether amine while preventing polyether amine intercalation

Polyether amine (PA) has recently been widely applied in water-based drilling fluid to improve shale stability. To study whether PA intercalation and the resulting increase of montmorillonite (Mt) d001-value have a negative effect on shale stability, a PA adsorption test on shale, a shale composites X-ray diffraction (XRD) test and a one dimensional swelling test of shale immersed in solution were conducted. PA can absorb on shale by exchanging Na⁺ in shale, resulting in a d001-value increase of sodium montmorillonite (Na-Mt) in shale and large vertical displacements, causing lots of micro cracks to develop in the shale with the shale matrix dispersed. For shale immersed in solution with KCl and PA mixed, PA intercalation was reduced and even prevented because K⁺ can exchange Na⁺ in the shale first. With the cation hydration reduced by K⁺ adsorption and the clay layer hydration decreased by PA adsorption on clay layer, vertical displacement was greatly reduced and stability was greatly enhanced for the shale immersed in solution with KCl and PA mixed. As a result, during drilling in shale containing Na-Mt, PA can cause shale instability. Using PA and KCl together can achieve better shale stability compared to using KCl only.