Pressure Control – Indicators of Increasing Pressure

•Pressure indicators are divided into two groups:
–I. Engineering.
–II. Geological.

Engineering Indicators of Increasing Pressure

•Changes in Rate of Penetration (ROP)
–ROP increases while drilling the transition zone.
–While drilling normally pressured shale sections, the ROP will decrease with depth if drilling parameters such as weight-on-bit, RPM, bit types, hydraulics and mud weight remain fairly constant.
–There will be a marked reduction in ROP as the pressure seal is penetrated.
–After penetrating the seal in sur-normally pressured formations, there will be an increase in ROP.
–This is due to the higher porosity of the sur-normal pressured zone.
•Decreases in dcsexponent trend
–Calculations for “d exponent”and “dcs exponent”can be made to normalize ROP data and predict the magnitude of increasing formation pressure.
–Trends can be graphically established using complicated formula
•Changes in rotary torque
–Rotary torque may increase rapidly in the transition zone.
–Torque increases gradually with depth because the contact friction between the drillstring and the wellbore increases with depth.
–Torque will increase in the transition zone because a larger volume of shale cuttings will enter the wellbore. Shale tends to close in the hole, causing additional contact with the drillstring and impeding bit rotation.
•Changes in drag
–An increase in drag may be experienced while making connections in the transition zone.
–After the kellyis drilled down, the recommended practice is to pick up 5 to 10 ft (to allow for working the drill pipe if it sticks), turn the pumps off and pull the kellyfrom the hole.
•Changes in rotary torque
–Extra cuttings may enter the wellbore when the transition zone is penetrated.
–The hole may also tend to close-in around the drill collars and bit.
–Some transition zone shales tend to flow under differential pressure.
–There have been instances where it was necessary to backreamand circulate to trip out of the hole.
•Kicks
–An actual kick is the most obvious indication of an increase in pressure.
–Any pit gain, if not accounted for, is an indication of an influx of formation fluid (kick).
–When this happens, the amount of fluid returning increases, and the flow sensor records the increase.
•Kicks Cont.
–When approaching a transition zone if an increase in pit volume or flow is detected, drilling should be stopped and the well checked for flow.
–If the well continues to flow, it should be shut in.
•Filling the hole on trips
–When pulling the drillstring out of the hole, the amount of pipe in the hole is reduced, and the mud level drops.
–The volume can be calculated from the size and weight of the pipe and the length of the pipe removed, so that an appropriate amount of mud can be pumped into the hole to fill it up.
•Filling the hole on trips
–If the drillstring volume is not replaced and the mud column drops, then the hydrostatic pressure is reduced and may result in a kick.
–If the hydrostatic pressure is reduced to less than formation pressure, formation fluids will flow into the well.
–If the hole takes less mud than the calculated displacement volume for the number of stands pulled, fluid is entering the wellbore.
–This signals an impending kick.