A reverse circulation is another way to circulate by circulating into annulus up to a bit and drill string. The fluid outlet is on surface. For drilling operation, we most of the time use forward circulation; however, in completion operation, the reverse circulation is utilized more often. For more understanding, we would like to show an image below (Figure 1) which demonstrates a flow path of the reverse circulation.
Figure 1 – Reverse Circulation
In this article, it will demonstrate the effect of frictional pressure on the bottom hole pressure and equivalent circulating density while the reverse circulation is performed.
Under a static condition:
The bottom hole pressure is equal to hydrostatic pressure from the drilling fluid.
Bottom Hole Pressure (BHP) = Hydrostatic Pressure (HP)
Under a dynamic condition:
Stand pipe pressure equates to summation of pressure loss of whole system.
Figure 2 – Pressure loss component during reverse circulation
SPP = FrPds + FrPbha + FrPbit + FrPann
Where;
SPP = Stand Pipe Pressure
FrPds = Pressure loss in drill string
FrPbha = Pressure loss in BHA
FrPbit= Pressure loss across the bit
FrPann = Pressure loss in Annulus
Please remember that the pressure loss acts opposite way while fluid is being moved.
For this case we can write the relationship of bottom hole pressure as shown in the following equation.
Bottom Hole Pressure = Hydrostatic Pressure + FrPds + FrPbha + FrPbit
Where;
FrPds = Pressure loss in drill string
FrPbha = Pressure loss in BHA
FrPbit= Pressure loss across the bit
The bottom hole pressure can be expressed in terms of the equivalent circulating density:
Where;
ECD = Equivalent Circulating Density, ppg
MW = Mud Weight in the well, ppg
FrPds = Pressure loss in drill string
FrPbha = Pressure loss in BHA
FrPbit= Pressure loss across the bit
TVD = True Vertical Depth, ft
References
Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.
Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.
Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.
Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.
Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.
