Experimental analysis on influence of flow regimes of drilling fluids within wellbore annulus on gas logging

Abstract While existing studies have investigated different influence factors for gas logging, the influence of flow regimes of drilling fluids in wellbore annulus—particularly such as concentric helical flow and gas–liquid two–phase flow—remains unclear. For this purpose, this study first derived key parameters of concentric helical flows (e.g., helical diameter, lead, and rotation direction), proposed a design of using helical pipe to achieve the concentric helical flow, and then validated the design by numerical modeling. Furthermore, this study identified generation conditions for various flow patterns in helical pipe and developed a gas measurement experiment to simulate both concentric helical flow and two–phase flow conditions. Experiments with concentric helical flows revealed: (1) total hydrocarbon content decreased with flow velocity increasing, with the impact remaining constant regardless of baseline velocity changed; (2) total hydrocarbon content decreased with higher mass flow rates, though the influence diminished as baseline mass flow rates increasing. Experiments with gas–liquid two–phase flows showed that: (1) total hydrocarbon content decreased with drilling fluid density increasing for all flow patterns, with different influence degree as flow patterns varying (Bubble flow > Plug flow > Slug flow > Annular flow > Mist flow); (2) total hydrocarbon content initially increased and then decreased with higher drilling fluid viscosity, while viscosity sensitivity decreased with flow pattern changes (Bubble flow > Plug flow > Slug flow > Annular flow > Mist flow); (3) total hydrocarbon content consistently increased with drilling fluid temperature increasing, and drilling fluid temperature exhibited the greater impact degree than drilling fluid density.