Development and Characterization of a Pressure Transmitting Sag Prevention Gel Pill

Abstract

Barite sag is a risky phenomenon to manage as particle settlement occurs in all types of drilling fluids containing weighting agents’ materials to achieve density. This leads to the phenomenon of sag which is known to complicate operations associated with construction and completion of wells in addition to other well control issues. Inert particle settling is a mechanism where particles separate from the liquid phase in which these originally were suspended in. This mechanism can change the hydrostatic fluid column as particle settlement create bed formations at the point of accumulation influencing the desired bottom hole pressure significantly. Operational conditions such as static periods or low circulation rates in deviated sections accelerate the particle sag mechanism and do often require remedial action when drilling is proceeded. This thesis work invented a sag prevention gel pill with barrier functionalities to controllably transmit hydrostatic pressure from the overlying fluid columns. Two gel pill designs based on bentonite and Laponite RD were characterized and tested in scaled up test setups to proof the concept and possible prevention of barite sag. The final target of investigation involved vertical, 20 and 40 degree inclined setups to simulate different sections of a well. The designed gel pill forms sufficient gel structure to isolate fluids placed below and above the pill column, but not such gel strength to act as a barrier blocking pressure signals. Thus, formation of gel structure was adequate to maintain barrier functionalities while transmitting pressure signals from the heavier water-based drilling fluid spotted on top, in addition to provide a foundation for the settled barite. Test results showed that the laponite-based pill provided even better performance during testing of both hindered and boycott driven particle settling. However, the bentonite-based pill provided better pressure transmitting communication throughout the test period.