Evaluation of low-gravity-solids sedimentation in non-Newtonian synthetic-based drilling fluids monitored by gamma-ray attenuation technique

Abstract

ABSTRACT Drilling fluids are used in the process of drilling wellbores. They are formulated by a combination of solubles and suspended solids. During drilling, cuttings of rock formation may get in the mix. Some of them are too small and light to be removed from the fluids. They are called low-gravity solids (LGS). In no drilling situations, both solids may settle due to gravity. This project aimed to characterize the physical and rheological properties of synthetic-based drilling fluids and monitor the distribution of solids concentration in batch gravity settling experiments. The interplay of solid content and mud rheology was evaluated by pycnometry, retort, and rheological analysis. The Gamma-ray Attenuation Technique was applied to monitor the solid concentration along the test tube as a function of time. We analyzed two similar muds that slightly differed by the presence LGS The fluids presented non-Newtonian behavior, clear separation of solids in two phases and apparent viscosity changes. After 90 days, the clarified liquid region was formed between 16 and 22 cm from the bottom of the tube. This region took shape between 7 to 80 days, and the maximum solid concentration was approximately 9%. Finally, the LGS increased the fluid resistance of settling.