Activity: Kick Causes - Total Loss of Circulation -

Problem 1: Zones of losses below the permeable zone 

In this case, the zone of losses is below the permeable zone where the formation fluids can come into the wellbore. There are three questions which can be faced in this activity. What is the equilibrium density at the permeable zone? To which level the column of drilling fluids will decrease? And finally, what will be the equivalent density at permeable zone when getting to equilibrium with the zone of losses? 

1. The equilibrium density at the permeable zone 

Ppore = 0.052 x deq x Z_per 

deq = Ppore / (0.052 x Z_per) 

deq = 6100 / (0.052 x 10000) 

deq = 11.73 ppg 

2. The level decrease of the mud column 

The losses stop when the bottom pressure will be in equilibrium with the zone of losses, so the column of mud will decrease till getting to the equilibrium. The equivalent density of the loss zone is " dequi = 11.26 ppg ", depending on this dequi, the equivalent pressure "Pequi" at this zone is: 

Pequi = 0.052 x dequi x Z_loss 

Pequi = 0.052 x 11.26 x 11700 

Pequi = 6850 psi 

The level of the drilling fluids will decrease to new depth (Z_new) to get to equilibrium with this pressure 

Pequi = 0.052 x MW x Z_new 

Z_new = Pequi / (0.052 x MW) 

Z_new = 6850 / (0.052 x 12.10) 

Z_new = 10887 ft 

So the level of the drilling fluids will decrease to a new depth of 10887 ft 

It decreased by 

H = Z_loss - Z_new 

H = 11700 – 10887 

H = 813 ft 

3. Will the well kick? 

To know if the well will kick or not, the equivalent density of the drilling fluids at the permeable zone has to be less than the related equivalent density of the permeable zone. 

The hydrostatic pressure of the new column of mud 

Phyd = 0.052 x MW x (Z_per - H) 

Phyd = 0.052 x 12.10 x (10000 - 813) 

Phyd = 5780 psi 

The equivalent density for this depth of the permeable zone is 

dequi = Phyd / (0.052 x Z_per) 

dequi = 5780 / (0.052 x 10000) 

dequi = 11.11 ppg 

We can see here that with this new situation the equivalent density at the permeable zone becomes less than the equivalent density which is related to the pore pressure (11.73 < 11.11), so the well will kick. 

Problem 2: Zone of losses above the permeable zone 

In the sketch, it is illustrated that the zone of losses is above the permeable zone. When facing a total loss of circulation, the level of mud column will decrease to certain level till getting to equilibrium with thieve zone. The question is "Will the well kick with these conditions? To answer this question some calculations have to be performed. 

1. The equilibrium density at the permeable zone 

Ppore = 0.052 x deq x Z_per 

deq = Ppore / (0.052 x Z_per) 

deq = 6100 / (0.052 x 10000) 

deq = 11.73 ppg 

2. The level decrease of the mud column 

Same as the example mentioned above in activity 1, the level will decrease till getting to equilibrium with the zone of losses. Then, the equivalent density is ''dequi = 11.25 ppg" 

Pequi = 0.052 x dequi x Z_loss 

Pequi = 0.052 x 11.25 x 6700 

Pequi = 3920 psi 

The level of the drilling fluids will decrease to new depth (Z_new) to get to equilibrium with this pressure 

Pequi = 0.052 x MW x Z_new 

Z_new = Pequi / (0.052 x MW) 

Z_new = 3920 / (0.052 x 12.00) 

Z_new = 6282 ft 

So the level of the drilling fluids will decrease to a new depth of 6282 ft 

It decreased by 

H = Z_loss - Z_new 

H = 6700 - 6282 

H = 418 ft 

3. Will the well kick? 

To know if the well will kick or not, the equivalent density of the drilling fluids at the permeable zone has to be less than the related equivalent density of the permeable zone. 

The hydrostatic pressure of the new column of mud 

Phyd = 0.052 x MW x (Z_per - H) 

Phyd = 0.052 x 12.00 x (10000 - 418) 

Phyd = 5980 psi 

The equivalent density for this depth of the permeable zone is 

dequi = Phyd / (0.052 x Z_per) 

dequi = 5980 / (0.052 x 10000) 

dequi = 11.50 ppg 

We can see here that with this new situation the equivalent density at the permeable zone becomes less than the equivalent density which is related to the pore pressure (11.73 < 11.50), so the well will kick. 

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