Effects of inhibitor KCl on shale expansibility and mechanical properties

Abstract The expansibility and mechanical properties of shale are significantly influenced by water-based muds (WBMs); thus, it is necessary to mitigate this effect to avoid borehole instabilities in drilling operation. Potassium chloride (KCl) is usually used as inhibitor to reduce hydration of shales. In this study, we investigated the inhibitory efficiency of KCl on shale through a series of experiments, including dynamic linear swelling (DLS) tests and uniaxial compressive strength (UCS) tests, to provide reference for the design of WBMs. These tests were conducted on shale samples soaked in KCl solution for 24, 48, 72, and 96 h with saline concentrations of 0%, 2%, 4%, 6%, and 8%. Experimental results show that samples with microcracks and bedding fissures have the highest swelling increase and the largest strength reduction after immersion in solution. The swelling potential decreased with increasing KCl concentration. In addition, KCl exhibited a certain inhibitory effect on the weakening of the mechanical properties of samples. An increase in the KCl concentration increases the compressive strength and elastic modulus, and decreases the Poisson's ratio. However, in terms of homogeneous samples, the UCS test results show that exposure to water is weakly related to weakening of the mechanical properties of shale samples. We found that immersing the shale in KCl solution for a longer time decreases the compressive strength, increases the Poisson's ratio, and decreases the elastic modulus.

[1]  Cnpc Drilling.  Status quo and challenges of global shale gas drilling and completion , 2011 .

[2]  Xianyu Yang,et al.  Influence of salt solutions on the permeability, membrane efficiency and wettability of the Lower Silurian Longmaxi shale in Xiushan, Southwest China , 2018, Applied Clay Science.

[3]  Yuanzhi Qu,et al.  Polyoxyalkyleneamine as shale inhibitor in water-based drilling fluids , 2009 .

[4]  Keith K. Millheim,et al.  Applied Drilling Engineering , 1986 .

[5]  R. Holt,et al.  Interaction Between Shale and Water-Based Drilling Fluids: Laboratory Exposure Tests Give New Insight Into Mechanisms and Field Consequences of KCl Contents , 1998 .

[6]  T. Al-Bazali.  The consequences of using concentrated salt solutions for mitigating wellbore instability in shales , 2011 .

[7]  T. Al-Bazali.  The impact of water content and ionic diffusion on the uniaxial compressive strength of shale , 2013 .

[8]  M. E. Hossain,et al.  Chemical and Mechanical Aspects of Wellbore Stability in Shale Formations: A Literature Review , 2014 .

[9]  R. Clark,et al.  Polyacrylamide/potassium-chloride mud for drilling water-sensitive shales , 1976 .

[10]  P. F. Low,et al.  Effects of monovalent, exchangeable cations and electrolytes on the relation between swelling pressure and interlayer distance in montmorillonite , 1995 .

[11]  Li Li.  Chemical and Mechanical Properties of Brittle Fractured Mud Shale , 2011 .

[12]  P. Horsrud,et al.  The Shrinkage Rate of KCL-Exposed Smectitic North Sea Shale Simulated By a Diffusion Model , 1998 .

[13]  R. Gholami,et al.  A review on borehole instability in active shale formations: Interactions, mechanisms and inhibitors , 2018 .