Amine shale inhibitors are an integral part of high-performance water based mud (HP WBM). There are many commercially available amines with similar claims regarding performance as shale inhibitors. Most performance comparisons are made relative to KCl-polymer muds, making the shale inhibitor differences very apparent. Unfortunately, a comparison between several good-performing inhibitors is rarely performed and reported. There are few systematic comparisons of amine shale inhibitors with each other based on their structure and conditions under which testing is performed. The relationship between amine structure and performance as an inhibitor is not well understood. This paper presents design of an experimental methodology to compare the effectiveness of 30+ amines as shale inhibitors under a broad range of testing conditions. Shale hydration, dispersion, and bulk hardness were measured after exposure to drilling fluids to determine which test parameter can most efficiently distinguish amines. Additionally, the adsorption or desorption of amines from a clay were measured to determine which amine is the strongest absorber. Statistical data treatment was applied to separate signal from the noise of measurements. The results of this investigation verified that amine inhibitors do not affect shale moisture content and shale dispersion is primarily affected by fluid viscosity. Furthermore, a bulk hardness test that measures cuttings hardness is a good differentiator of amine inhibitors. Supplementary functioning for amine inhibitors was confirmed with adsorption or desorption test that showed good correlation with a bulk hardness test. In summary, these measurements established a structure-activity relationship between the amines tested and determined that an effective shale inhibitor should contain more than 1 nitrogen atom/molecule. Additionally, linear structure is preferred over branched structure, and supplementary hydrophobic amines function better than hydrophilic amines provided the amine remains water soluble. Amines were further differentiated by their acid-base dissociation constant (pKa). The reason some amines perform in broader pH range than others is also presented. For the first time, a statistically validated study has been conducted to assess the results of different tests and to compare the effectiveness of different shale inhibitors. The results of these comparisons provided a way to understand the shale inhibition mechanism and develop better practices focused on developing next-generation aqueous fluid systems.

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