We still have the same question as the previous post, Pressure Loss and Equivalent Circulating Density Review, but this case we will do reverser circulation, circulating from annulus to tubing , and see how much pressure and equivalent circulating density at bottom hole.
Reverse circulate total of 3 time bottom up from annulus to tubing with 12.7 ppg mud at 10,000’MD/10,000 TVD.
Pump pressure = 1000 psi
Annulus friction loss = 50 psi
Inside tubing friction loss = 925 psi
Surface line friction loss = 25 psi
Determine pressure at bottom hole.
We still apply the concept of frictional pressure so reverse circulation is calculated by this following equation:
Pressure at bottom hole (reference at annulus side) = Hydrostatic Pressure + Pressure from pump- Annular Pressure Loss
Note: Hydrostatic pressure and pressure from pump force downward to bottom hole but annulus pressure forces upward direction.
Pressure in the well at 10,000’ = 1000 + (0.052×10,000×12.7) – 50 = 7554 psi
OR you can referrence to the tubing side as well.
Pressure at bottom hole (reference at tubing) = Hydrostatic Pressure + Annular Pressure Loss in tubing + surface line pressure loss
Note: All pressure force downward to bottom hole so all pressure term must be sum together.
Pressure at bottom hole (reference at tubing) = (0.052×10,000×12.7) + 925+25 = 7554 psi.
Determine Equivalent Circulating Density at bottom hole.
ECD = Current mud weight in PPG + (annular pressure loss /(0.052xTVD)) = Total Pressure at Bottom Hole /(0.052xTVD)
ECD =7554 / (0.052 x 10,000) = 14.53 PPG.
The point that I want you to think of between this example and the previous example, Pressure Loss and Equivalent Circulating Density Review, is about the different of bottom hole pressure and ECD between forward circulation and reverse circulation.
You will see that reverse circulation results in a lot of pressure at bottom hole. Hence, you must keep in mind this concept and try to figure out how much pressure at bottom hole should be for both forward circulation and reverse circulation. Otherwise, you can accidentally break wellbore due to high ECD.