Synthesis of superhydrophobic nanofluids as shale inhibitor and study of the inhibition mechanism

摘要

In this work, an effective shale inhibitor, superhydrophobic SiO2 (SH-SiO2) nanomaterial, was easily synthesized using five different silane-coupling agents through sol-gel method. The characteristics of SH-SiO2 were examined, and results indicated that spherical nanomaterials with a diameter of approximately 100 nm were successfully prepared. These nanomaterials easily adsorbed onto the shale surface, changed the surface structure, and dramatically altered the surface wettability with increased water-contact angle from 35 degrees to 150 degrees. These nanomaterials were stable at 400 degrees C. SH-SiO2 inhibition was further evaluated by hot-rolling recovery bentonite linear swelling tests, as well as spontaneous-imbibition measurement. Results showed that SH-SiO2 had excellent inhibition ability better than that of the commonly used inhibitors potassium chloride (KCl), poly (ester amine), and nano-SiO2. Inhibition-mechanism analysis revealed that SH-SiO2 enhanced shale inhibition through surface adsorption, wettability alteration, and electron interaction. First, SH-SiO2 adsorbed onto clay minerals due to the low-surface free energy and induced a change in the surface microstructure. Then, several clay minerals assembled, leading to increased particle size. Second, SH-SiO2 altered surface wettability from hydrophilic to superhydrophobic and reverse the capillary force. Water invaded the particle voids and the interlayering of clay minerals was prevented. Third and last, electron interaction occurred between the protonated amino on SH-SiO2 and the negative group of Na-BT. Less water from drilling fluid came in contact with the shale formation. As a result, shale inhibition was enhanced and the wellbore stability was kept.