Improving the performance of a polyamine shale inhibitor by introducing a hydrophobic group in oil and gas development

Abstract

Wellbore instability in complex shale formations is a major technical problem that threatens drilling safety and efficiency. In this paper, a hydrophobic cationic polyamine shale inhibitor (HCPA) was prepared by introducing a hydrophobic group in the molecular structure of an amine-based shale inhibitor having a branched structure. The shale inhibition performance of HCPA and the amine-based shale inhibitor without the hydrophobic group (CPA) was investigated. The hydration inhibition mechanism of HCPA was studied by experiments of zeta potential, particle size, contact angle, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), etc. The evaluation results show that HCPA had a better performance than CPA in terms of inhibition of hydration swelling, hydration dispersion and mud making, which indicates that the hydrophobic group is beneficial to improve the inhibition ability of the amine-based shale inhibitor. The mechanism study shows that there is no hydrogen bond between HCPA and clay. The adsorption on the clay surface is mainly driven by electrostatic interaction, which reduces the repulsion of the electric double layer and thus inhibits the osmotic swelling of clay. HCPA could increase the water contact angle of the rock from 36.6° to 133° at a concentration 0.5%, beneficial to reduce surface free energy. The bentonite modified by HCPA had a lower weight loss of at 200 °C than bentonite modified by CPA according to TGA test, and the interlayer spacing of HCPA-modified bentonite was reduced compared with that of the unmodified bentonite, indicating that the ability of bentonite to adsorb water molecules is reduced after the introduction of hydrophobic groups, beneficial to inhibit the crystalline swelling of clays. In addition, HCPA can reduce the imbibition capacity of rocks by reducing the surface tension of water. Therefore, the concept of introducing hydrophobic groups in the molecular structure proposed herein could provide an avenue to develop high-performance shale inhibitors.