During a well start-up, fluid distribution within the well shifts from a static segregated phase (gas-oil-water) column to a flowing three-phase mixture. For this transition to be successful, the well has to overcome the additional hydrostatic head associated with the phase segregation. This process can be problematic for wells with limited pressure support as an improper bean-up procedure can lead to a situation where the pressure driving force across the well is unable to overcome the hydrostatic head imposed by the liquid column during start-up thus resulting in a failed start-up. The failed start-up may add extra liquid present within the wellbore thus making subsequent start-up attempts even more difficult. For such wells, correct bean-up strategy is important to ensure successful start-up.

In the current work, dynamic simulations are conducted with a commercial transient-multiphase-simulator to understand the start-up flow and pressure transients and optimize the start-up procedure of a lazy horizontal oil well which has experienced start-up problems after a resting period.

Simulations of the failed bean-up procedure showed that a water-lock formation in the tubing hampers a successful well start-up as the hydrostatic head imposed by the water-lock does not allow the well to flow. An alternate bean-up procedure was then virtually tested by simulation where the wellhead choke was quickly opened. This led to a successful start-up as a gas pocket originally trapped in the horizontal section could escape to the vertical tubing only under quick bean-up thus lowering the hydrostatic pressure below the pressure driving force across the well. Dynamic simulations were also used to devise a strategy for the operator as to how long the well be rested before any bean-up is attempted. The proposed strategy enabled the operator to use the readings from downhole pressure gauge as a guide in deciding the resting period and bean-up procedure.

This study brings forth the significance of dynamic simulations in optimizing the start-up of lazy wells where failed bean-ups can lead to higher down times thus adversely affecting production. Further, dynamic simulations also help in arriving at guidelines for the operators on how to avoid failed start-ups.

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