Experimental Characterization of Linear Swelling of Reactive Clays Dominated Wells: Comparison of Drilling Fluid Systems

Shale drilling remains one of the oil industry's most challenging and expensive operations. One of the main concerns in shale drilling is the instability of the wellbore, which can be attributed to the physio-chemical interaction between the drilling fluid systems and the shale formation. This poor interaction is primarily caused by the presence of high-reactive clays, which are known to cause swelling and dispersion issues during drilling. This paper evaluates the linear swelling characteristics of a shale formation dominated by high-reactive clay. A comparative analysis of various drilling fluids’ performance in controlling shale swelling is performed for four (4) clay-dominated wells drilled in the Tuscaloosa Marine Shale (TMS). The mineralogy concentration of samples obtained from different wells drilled in the shale formations is characterized using Fourier-transform infrared spectroscopy (FTIR). Additionally, clay swelling tests are performed in accordance with the American Society of Material Testing (ASTM) Standard Section D5890 to determine the swelling indices of the wells under investigation when exposed to different drilling fluid systems. The study reveals that all the wells tested have a clay concentration of at least 50%. Furthermore, the choice of drilling fluid systems significantly affects the swelling rate. High-performance water-based mud (HPWBM) systems, such as KCl and high salinity formate brine, exhibit improved swelling inhibition and compatibility with high-reactive shale formations. The study revealed that the use of high-performance water-based systems reduces the swelling tendency of clay by as much as 60% compared to conventional water-based systems. The use of inhibitive mud systems also minimized the size of the opening of the tetrahedral sheet of the clay during water invasion as opposed to the conventional water-based mud systems.