Master of Science in Petroleum Engineering (MSPE)
Sustained Casing Pressure (SCP) is the undesirable casing head pressure of a well annulus that rebuilds when bled-down. As the conventional methods for SCP removal using rigs are expensive, there is a need for improvement. Annular intervention for replacing the fluid above the leaking cement with a heavier fluid to stop gas migration is a solution for SCP removal; however, previous attempts failed due to miscibility of injected fluids. Using hydrophobic heavy fluids for the purpose is a newly proposed technique to the technology. Potential of theoretically selected and produced immiscible heavy fluids are investigated in characterized annular fluids. A transparent laboratory scaled-down hydraulic analog of well’s annulus provided visual evidence for displacement geometry and did the first stage testing of heavy fluid injection into clear synthetic-clay muds. A 20-foot physical model then tested the performance of the displacement process. Settling of various heavy fluids with densities from 11 to 23 ppg in drilling fluids with densities from 9 to 13 ppg provided quantitative bottom pressure data. Finally, a full-size test in 2750-foot well examined the viability of the technology. Visualization experiments proved that the counter-current flow in annulus leads to up-lifting of heavy fluid droplets and must be minimized for a desirable displacement process. Selection of injection geometry and rate are also essential to maintain a controlled transport of heavy fluid downwards. Pilot experiments developed mathematical correlations relating the process performance to fluid properties and rate. Full-size test shows that hydrophobic heavy fluids are able to slip in long columns; however, bridge-over of buoyant settling may occur due to high injection rates and/or flotation effect of migrating gas that was entrapped in annular fluid. The findings in this research present solid support to the viability of immiscible gravity displacement of annular fluid for remediating a well annulus affected with SCP. For given fluid properties and in confined annular space, injection rate is the key to a successful displacement. Finally, the research proved that the duration of a complete displacement process and required heavy fluid volume are inversely correlated. For any operation design; time and killing material restrictions must be considered.
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Demirci, Efecan, "Removal of Sustained Casing Pressure by Gravity Displacement of Annular Fluid" (2014). LSU Master's Theses. 3535.