Study on the formation mechanism of a flat rheology by poly(diethylenetriamine dimer acid amide) and organoclay in nonaqueous drilling fluids over a wide temperature range

Abstract

This work aims to establish the relationship between the morphology and rheology changes affected by the addition of Flat-rheology modifier (FRM) to organoclay (OC)/white oil dispersions between 2 and 65 °C to analyze the flat-rheology formation mechanism in nonaqueous drilling fluids. The FRM used in this work is poly(diethylenetriamine dimer acid amide), and the OC is organo-montmorillonite. Temperature-controlled rheological tests confirmed that FRM addition to dispersions with low OC loadings (lower than 3.0 wt%) results in a relatively constant gel strength from 2 to 65 °C. This could be explained by the morphology variations in the dispersions generated by the FRM. Based on macroscopic settlement, particle size distribution, optical microscopy, transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS) results, FRM molecules were inserted into and enlarged the interlayer space between OC platelets, thus reducing the particle size and improving the dispersion stability. Subsequently, the original card house network formed by OC particles was destroyed, and a new network with a larger volume fraction was formed by the highly dispersed platelets and FRM molecules. The increase in network volume fraction and extension of FRM molecular carbon chains with increasing temperature inhibit network strength deterioration. As a result, the rheological properties at 65 °C remained similar to those at 2 °C, thereby forming a flat rheology.