Study of the Rheological Properties of High-Density Oil-Based Drilling Fluid Considering Wall Slip Effect

Wall slip effect seriously affects the accurate measurement of the rheological properties of high-density oil-based drilling fluids, and it needs careful detection and correction. A correction method for the wall slip effect during the measurement of the rheological properties of high-density oil-based drilling fluids was established based on the Tikhonov regularization method. Rheological property measurement experiments of high-density oil-based drilling fluids in deep shale gas wells considering wall slip effect were carried out using a six-speed rotational viscometer, and the wall slip characteristics of high-density oil-based drilling fluids were analyzed. The rheological model was optimized and the rheological parameters were calculated. The calculation results demonstrate that, when compared with the rheological parameters before correction, the dynamic shear force of high-density oil-based drilling fluids in deep shale gas wells is reduced after correction, while the liquidity index is increased to nearly 1.00. The results demonstrate the real rheological properties can be expressed by Bingham model. When the wall shear stress is higher than the critical shear stress, the slip velocity will increase exponentially with increasing wall shear stress.The results show that a slip effect exists during the measurement of the rheological properties of high-density oil-based drilling fluids. It demonstrates, too, that the rheological model and rheological parameters before and after slip correction are significantly different, and the influence of slip effect should be eliminated for accurate measurement.