What are the best well control practices for tripping in depleted reservoirs?

1 Use a trip margin

A trip margin is the amount of extra pressure that is added to the mud weight to account for the swabbing effect that occurs when the drill string is pulled out of the hole. Swabbing is the reduction of pressure in the annulus due to the upward movement of the drill string, which can create a suction force that draws formation fluids into the wellbore. By using a trip margin, you can ensure that the hydrostatic pressure remains higher than the formation pressure at all times, preventing any influx of formation fluids. However, you need to be careful not to use too large a trip margin, as this can increase the overbalance and cause more fluid losses. A typical trip margin is 100-200 psi, but it may vary depending on the well conditions and the type of drilling fluid.

2 Monitor the hole fill

Another important well control practice for tripping in depleted reservoirs is to monitor the hole fill during the trip. The hole fill is the volume of drilling fluid that is pumped into the wellbore to replace the volume of the drill string that is removed. By monitoring the hole fill, you can detect any discrepancies between the expected and actual volumes, which can indicate fluid losses or gains. Fluid losses can occur when the drilling fluid leaks into the formation due to overbalance, while fluid gains can occur when formation fluids enter the wellbore due to underbalance. Both situations can compromise well control and require corrective actions. Therefore, you should use a trip tank or a flow meter to measure the hole fill and compare it with the calculated volume based on the drill string dimensions and the depth.

3 Perform flow checks

A flow check is a simple but effective well control practice that involves stopping the mud pumps and observing the flow out of the wellbore. A flow check can help you identify any signs of wellbore influx, such as bubbles, gas-cut mud, or increased flow rate. A flow check should be performed at regular intervals during the trip, especially before pulling out of the hole, after reaching surface, and before running in the hole. If you detect any flow during a flow check, you should shut in the well and perform a well control procedure to circulate out the influx and restore the hydrostatic pressure.

4 Use a backpressure pump

A backpressure pump is a device that can be used to apply a controlled amount of pressure to the annulus during tripping in depleted reservoirs. A backpressure pump can help you reduce the overbalance and fluid losses by lowering the hydrostatic pressure of the drilling fluid, while maintaining enough pressure to prevent any influx of formation fluids. A backpressure pump can also help you avoid surge pressures that can occur when the drill string is run into the hole, which can damage the formation and cause fluid losses. A backpressure pump can be operated manually or automatically, depending on the system and the operator preference. However, you need to be careful not to reduce the pressure too much, as this can create an underbalance situation and cause an influx.

5 Here’s what else to consider

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