Shale Inhibitor Tracking for High-Performance Water-Based Drilling Fluids
Authors: May Preston , Deville Jay P. , Miller Jeffrey 
Published: March 2022

Abstract
Drilling wells with water-based fluid systems can be problematic due to the water reactivity of clay-containing shale minerals. This fundamental issue is the most often cited performance gap between non-aqueous fluid (NAF) and water-based fluids (WBF). The consequences of uncontrolled shale hydration include issues such as bit-balling/accretion, reduced ROP, wellbore collapse, and overall increased wellbore construction costs. This problem is typically addressed by the addition of shale inhibitors which can span multiple types of chemistries. The maintenance of these additives is nuanced due to their inherent depletion on reactive minerals leading to uncertainty of active concentration of these additives during a drilling campaign. Considering the critical need to maintain concentrations of these additives, uncertainty is not an optimal plan to ensure success. To this end, we have designed quantitative shale inhibitor tracking technology to measure amine-based shale inhibitors in high-performance water-based fluids. The method is robust, detects only amine-based swelling inhibitors, and is fully amenable to be performed at a rig site.
We developed a colorimetric assay that quantitatively measures amine-based shale inhibitors in filtrates of WBFs. The reaction to generate color utilizes proprietary reagents that selectively target only the amines of interest, and is not influenced by nitrogen-containing polymers such as polyacrylamides. Additionally, the results of the test are not influenced by any common drilling fluid additives, including black powders. The colored solutions produced in the test are measured by advanced spectroscopic analysis with a handheld, portable field meter at a specific wavelength. The absorbance is used to determine the concentration of the amine inhibitor in the fluid filtrate. Finally, we have tested reliability of the method through numerous approaches including Gage Repeatability and Reproducibility statistical analysis.
With this new technology, we have explored amine depletion on reactive clays in a lab setting, uncovering unique depletion rates based on amine chemistry. Additionally, we have trialed this technology in multiple wells. We have validated the test method and equipment to be field friendly and accurate, as designed. Our field engineers have included this new measurement alongside a typical mud check. In our validation trials we have already observed different depletion rates based on well and operational procedures for amine inhibitor maintenance, and conflicting values of measured concentrations and product concentration estimates based on calculations.
We have coupled high-performance fluid design with shale inhibitor tracking technology to reduce the uncertainty of WBF chemical composition. This technology will allow us to sustain effective concentrations of high-performance additives and improve operational reliability throughout the wellbore construction process. Furthermore, this technology will allow more effective re-use of WBF, reducing the environmental impact of our fluids, and lowering well costs.