SICP and SIDPP

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SICP and SIDPP

SICP = Shut- In Casing Pressure

SIDPP = Shut- In Drill Pipe Pressure

Both the terms are self-explanatory that both the pressures are the property to be measured when the well is Shut-In i.e when BOP is closed (mostly at instances of KICK). SICP is the pressure build up in the annular area between casing and drill pipe. While SIDPP is the pressure build up in the Drill Pipe.

After shutting the well vital Well control information can be obtained from both SICP and SIDPP that can be measure from the casing and drill pipe pressure gauge located at the surface.

Both the pressures are giving information of the Bottom Hole conditions.

To understand even clearly refer the following Figure 1

Figure 1

Visualize the bottle of Coke with open cap (do not shake the bottle and open cap slowly). Press your hand tight on the mouth of the bottle and shake the bottle hard. You will feel the pressure on your hand and inside fluid will exert pressure trying to come out of the bottle. Though there was no pressure initially, but pressure was because of dissolved gas in coke.

Same is the concept of SICP and SIDPP. Though formation pressure is balanced, during influx of formation fluid they will exert the pressure against the HP of mud column. This excess pressure is what we call it SICP and SIDPP. Its necessary to close well so as to know the increased pressure.

This vital information will help in knowing what amount of mud weight shall be increased to balance the increased Formation Pressure ( now onwards FP).

Mostly SIDPP is less than SICP

• The reason is kick fluids will either be oil or gas (in almost cases). Both are lighter than mud (i.e water in general) . So HP in casing (because kick fluids migrate through casing) by fluids (Drilling Mud + Kick Fluid) will be less than HP in drill pipe by fluids (pure drilling mud )

As,

                SICP = FP- HP (By fluid column in annular area between casing and Drill Pipe)

                SIDPP = FP- HP (By Fluid column in Drill Pipe)

HP _casing < HP _{drill pipe} 

So,          SICP > SIDPP

•  For the case when the weight of mud cuttings in the casing surpasses the reduction in HP in casing due to kick fluid, in that case HP of casing is greater than Drill pipe and hence

HP_casing ( Mud + Kick + Heavy Cuttings) > HP_{drill pipe} (pure Mud)

             SIDPP > SICP

It is important to know which type of Kick Fluid has got in. That can easily be found out from SICP, SIDPP and known weight of Drilling Mud and from Pit Gain from Mud Pit

Calculation is done by Karan Patel for sake of understanding 

Effect of Gas Migration in SICP

  

Image taken from the site "drillinghandbook.com" as a reference to understand the topic

                          [ Try to understand the highlighted part (red color) from the image]

As shown in the figure above, when the well is closed the Gas migration provides increasing Casing Pressure and Simultaneously it increases Bottom Hole Pressure.

It is necessary to change Mud weight so as to counter increased formation pressure which caused Kick to enter well bore. But as SICP does not provide the correct information because of Kick fluids, Formation Pressure is calculated from SIDPP.

And on the basis of known increased FP weight of Kill Mud is decided and is circulated through out the well.

Note : AS Gas Migrates SICP keeps on increasing, but it should not exceed predetermined pressure handling capacity for particular Grade of Casing or else will result in failure of casing by bursting. And increased Bottom Hole pressure also results into Formation Damage and resulting into lost circulation. So while migrating the Gas Kick or any Influx out of the well, SICP should be held constant with the opening/closing of valve in return line which goes to choke manifold.