Experimental and modelling of the impact of quaternary ammonium salts/ionic liquid on the rheological and hydrate inhibition properties of xanthan gum water-based muds for drilling gas hydrate-bearing rocks

In this study, quaternary ammonium salts (QAS) and ionic liquid (IL) were used as additives in xanthan gum water-based muds formulations to investigate their rheological and hydrate inhibitive potentials in drilling gas hydrate sediment. The QAS/IL used were TMABr, TP(r)ABr, TMACl, and EMIMCl. The mud rheological characterisation was performed at a controlled shear rate of 1 s(-1) to 200 s(-1) at -2 degrees C-40 degrees C. The hydrate test was conducted in a high-pressure reactor at 8 MPa and -2 degrees C. The hydrate nucleation onset time was predicted using the classical nucleation theory (CNT) model. The rheology and hydrate results confirmed the potential application of QAS/IL in drilling mud formulations for drilling hydrate sediments. The presence of QAS/IL in the base mud suitably reduced the mud viscosity and yield stress, which are desired properties for generating turbulent flow to enhance cuttings transport, especially in high angle wellbores. The rheological properties of water-based mud were found to be significantly controlled or affected by the cation, anion, and alkyl chain length type of QAS/IL. However, the anion effect is more dominant and exhibit a critical concentration depending on its respective ionic strength. Further FTIR analysis confirmed the presence of N-O stretching which supports the performance of TMA(+) over EMIM+ to reduce the mud yield stress. In addition, the thermal degradation of the base mud was significantly reduced in the presence of QAS/IL. Amongst the studied additives, TMACl and TP(r)ABr WBMs completely prevented hydrate plugs in the mud system. Furthermore, the CNT model accurately predicted the hydrate onset time with APE < 2%. The QAS/IL in the WBM systems exhibited minimal to negligible disturbance (< 0.5 K shift) on the methane hydrate phase boundary compared with commercial hydrate additives at 3 wt%. This study provides guidelines to design efficient QAS/IL WBMs for drilling gas hydrate rocks.