Abstract
Due to the effects of wellbore storage, shut-in period allows additional inflow of gas bubbles into the annulus. Wellbore and casing pressures rise during shut-in of a gas kick as a consequence of gas upward migration and gas compressibility, which will threaten the safety of well control. Therefore, the variation law of surface and wellbore pressures for a gas kick well during shut-in should be investigated. Based on wellbore storage effect, a new model to the wellbore and casing pressure build-up during shut-in for a gas kick well is developed in this paper. Simulation results show that at different gas kick volumes, the rate of bottom-hole pressure rise increases as the permeability decreases. And surface casing pressure stabilizes quickly for low permeable formations. However, at equal initial annular gaseous volume, the rates of rise of the bottom-hole and surface casing pressures for low permeable formations are slower than for high permeability formations.
Highlights
A with increase in shut-in time that can lead to weak formation gas phase is considered highly compressible
All of the currently existing models for pressure analysis are based on gas upward migration
The rate of bottom-hole pressure rise increases as the permeability decreases. This is because at the time of noticing a gas-kick on surface equipment, drilling a low permeable reservoir would have caused a smaller volume of gas inflow into the annulus than drilling the same interval into a higher permeable reservoir
Summary
Due to the effect of wellbore storage, shut-in period with no further expansion after well complete closure. Such compression results in increased gas mass of the entire annular gaseous phase at instantaneous time t+Δt for the constant annular gas. The rate of bottom-hole pressure rise increases as the permeability decreases This is because at the time of noticing a gas-kick on surface equipment, drilling a low permeable reservoir would have caused a smaller volume of gas inflow into the annulus than drilling the same interval into a higher permeable reservoir. This is because for the same reservoir pressurization and equal initial annular gas volume at the time of complete well shut-in, the higher rate of gas inflow from the 300 or 400-md formations would continuously introduce larger quantity of gas mass into the annulus than the 50-md formation.
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