Basic Understanding of Underbalanced Drilling

Between the fracture pressure and the pore pressure of the formation, the hydrostatic pressure of drilling fluid will always be maintained according to conventional drilling practice. In order to control the transport cuttings to the surface as well as the formation fluids, the drilling fluid is held within the wellbore where it circulates. Furthermore, it also keeps the drill bit cool and lubricated as it acts as a stabilizing agent. For effective use, the fluid must be water- or oil-based and this leads to a maximum weight of 19 pounds for each gallon (minimum of 7.8 pounds). As an attempt at imparting fluid loss, density, and rheological properties, it also contains a mixture of liquid and solid products.

Figure 1 - Conventional Drilling

Figure 1 – Conventional Drilling

For many years, the conventional drilling has been the safest method when drilling a well but there are also some negatives to using the method. For example, fluid invasion is a common problem because the drilling fluid pressure is naturally above the pressure of the natural formation – this can cause permeability damage. Also, physical blockages and washouts are common as the solids and fluids lodge into the formation. Continue reading

Well in an Unbalanced Condition (Video)

The well is in an underbalanced condition while pulling out of hole. You can see in the video below that the fluid is flowing up from the drill pipe side. It is such very important to understand the condition of the well and have the plan to deal with it.


These are some thought about this situation from our member in the Facebook fanpage.

Hossam Hamza – Looks like it was failed balanced cement plug job, I see long cement chiksan line on rig floor and circulating head connected with low TQ valve above 1 joint DP in mouse hole, the back flow due to over displacement. Is my guess right???? Continue reading