Colorimetric Determination of Amine-Based Shale Inhibitors in Water-Based Drilling Fluids

Formations that contain hydratable shale or mixed layers of reactive clay can lead to wellbore instability issues during drilling operations. Shale inhibitors are used to limit the interaction of water with clay particles. Amine-based compounds are commonly used shale inhibitors in water-based drilling fluids. Amine-based shale inhibitors are typically added in predetermined concentrations in water-based drilling fluids. The shale inhibitors prevent the swelling and disintegration of shales, preventing problems during the drilling process, such as wellbore instability, viscosity build-up, high torque and drag, bit balling and stuck pipe, and wellbore caving. During the drilling process, the shale inhibitors are either consumed or may be lost to the formation. Accordingly, there exists a need for quantifying and tracking active concentrations of amine-based shale inhibitors in drilling fluids in real-time conditions. The paper describes a method for quantifying and tracking an amine-based shale inhibitor in a drilling fluid through UV-visible spectrophotometry. The method involves reacting the amine-based shale inhibitor with a complexing agent and then measuring the absorption intensity of the residual complexing agent solution using a portable UV-visible spectrophotometer. For varying concentrations of an amine-based shale inhibitor, a correlation between a concentration of the amine-based shale inhibitor in a water-based drilling fluid and an ultraviolet (UV)-visible absorption intensity is determined. A calibration plot is generated from the correlations. Samples of a circulating drilling fluid having unknown concentrations of amine-based shale inhibitor are collected. The concentrations of amine-based shale inhibitor in the samples of the circulating drilling fluid are estimated using the calibration plot. The method of colorimetric determination of amine-based shale inhibitors in water-based drilling fluids was field validated successfully. The method was successful in tracking the depletion rates and any addition of the amine-based shale inhibition in the water-based drilling fluids during drilling.