Understand U-Tube Concept and Importance of U-Tube

We can likely use the behavior of one of the fluid columns to describe behavior regarding what is happening in another side of fluid column, if two fluid columns are connected at bottom. Basically, this situation is simply described in common oil filed name as “U Tube”.

In oil field especially drilling business, “U Tube” can be considered as a string of pipe (drill pipe and tubing) is in a wellbore and fluids are able to pass inside of string of pipe (drill pipe and tubing) and the annulus (area between wellbore and string of pipe). The figure below demonstrates “U Tube” in our drilling business.

Why is U-Tube very important?

It is very vital to keep a basic concept of U-Tube in mind.

If there are two different fluids between inside of string and annulus, fluids always flow from a higher pressure area to a lower pressure.

If the system is NOT closed, lighter fluid will be flown out and it will be stopped when system pressure is stabilized (see figure below).

If the system is closed, pressure must be the same at the bottom point where both sides of U-tube are connected. Therefore, drill pipe pressure and casing pressure (annulus pressure) will be responded based on fluid in each side and formation pressure at bottom hole (see figure below).

Please always remember that U-Tube concept can be widely applied in many drilling and workover application such as well control, cementing, etc.

Reference book: Well Control Books

What is Tertiary Well Control?

Can you imagine if primary and secondary well control are failed? Well is flowing all the time so how can we deal with this situation? For this situation, you must use Tertiary Well Control.

Tertiary Well Control is specific method used to control well in case of failure of primary and secondary well control. These following examples are tertiary well control:

    • Drill relief wells to hit adjacent well that is flowing and kill the well with heavy mud.

BP Macondo Well – Relief Wells

    • Dynamic kill by rapidly pumping of heavy mud to control well with Equivalent Circulating Density (ECD)
    • Pump barite or gunk to plug wellbore to stop flowing
    • Pump cement to plug wellbore

Reference book: Well Control Books

What is Secondary Well Control?

Referring to the previous section, primary well control is hydrostatic pressure bore that prevents reservoir influx while performing drilling operations (drilling, tripping, running casing/completion, etc). When primary well control is failed, it causes kick (wellbore influx) coming into a wellbore. Therefore, this situation needs special equipment which is called “Blow Out Preventer” or BOP to control kick.


Blow Out Preventer

We can call that “Blow Out Preventer” or BOP is Secondary Well Control. Please also remember that BOP must be used with specific procedures to control kick such as driller method, wait and weight, lubricate and bleed and bull heading. Without well control practices for using BOP’s, it will just be only heavy equipment on the rig.

There are several types of “Blow Out Preventer” (BOP) which have different applications. we will talk about BOP categories later.

Reference book: Well Control Books

What is Primary Well Control?

Primary Well Control is hydrostatic pressure provided by drilling fluid more than formation pressure but less than fracture gradient while drilling. If hydrostatic pressure is less than reservoir pressure, reservoir fluid may influx into wellbore. This situation is called “Loss Primary Well Control”.

Not only is hydrostatic pressure more than formation pressure, but also hydrostatic pressure must not exceed fracture gradient. If mud in hole is too heavy, it will cause a broken wellbore, you will face with loss circulation problem (may be partially lost or total lost circulation). When fluid is losing into formation, mud level in well bore will be decreased that will result in reducing hydrostatic pressure. For the worst case scenario, you will lose the primary well control and wellbore influx or kick will enter into wellbore.

Typically, slightly overbalance of hydrostatic pressure over reservoir pressure is normally desired. You must keep in mind about the basic of maintaining primary well control that you must maintain hole with drilling fluid that will be heavy enough to overbalance formation pressure but not fracture formations.

Reference book: Well Control Books

Oil Field Coversion Part 3 Oil Field Conversion Part 3 – Pressure,Velocity,Volume,Weight

The last part of unit conversion is the conversion for  Pressure,Velocity, Volume and Weight specially used in the oilfield.

The RED number is the conversion unit.


Atmospheres x 14.696 = Pounds/sq inch

Atmospheres x 1.033 = Kilograms/sq cm

Atmospheres x 101300 = Pascals

Kilograms/sq cm x 0.9678 = Atmospheres

Kilograms/sq cm x 14.223 = Pounds/sq inch

Kilograms/sq cm x 0.9678 = Atmospheres

Pounds/sq inch x 0.068 = Atmospheres

Pounds/sq inch x 0.0703 = Kilograms/sq cm

Pounds/sq inch x 0.006894 = Pascals


Feet/sec x 0.305 = Meters/sec

Feet/mm x 0.00508 = Meters/sec

Meters/sec x 196.8 = Feet/mm

Meters/sec x 3.28 = Feet/sec


Barrels x 42 = Gallons

Cubic centimeters x 0.00003531 = Cubic feet

Cubic centimeters x 0.06102 = Cubic inches

Cubic centimeters x 0.000001 = Cubic meters

Cubic centimeters x 0.000264 = Gallons

Cubic centimeters x 0.001 = Litters

Cubic feet x 28320 = Cubic centimeters

Cubic feet x 1728 = Cubic inches

Cubic feet x 0.02832 = Cubic meters

Cubic feet x 7.48 = Gallons

Cubic feet x 28.32 = Litters

Cubic inches x 16.39 = Cubic centimeters

Cubic inches x 0.0005787 = Cubic feet

Cubic inches x 0.00001639 = Cubic meters

Cubic inches x 0.004329 = Gallons

Cubic inches x 0.01639 = Liters

Cubic meters x 1000000 = Cubic centimeters

Cubic meters x 35.31 = Cubic feet

Cubic meters x 264.2 = Gallons

Gallons x 0.0238 = Barrels

Gallons x 3785 = Cubic centimeters

Gallons x 0.1337 = Cubic feet

Gallons x 231 = Cubic inches

Gallons x 0.003785 = Cubic meters

Gallons x 3.785 = Liters


Pounds x 0.0004535 = Tons (metric)

Tons (metric) x 2205 = Pounds

Tons (metric) x 1000 = Kilograms

Ref book: Drilling Formula Book Formulas and Calculations for Drilling, Production and Workover, Second Edition