Category Archives: Well Control

The Deepwater Horizon Got Explosion and Fire – 12 People Missing

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I just saw NEWS from the TV showing The Deepwater Horizon Got Explosion and Fire – 12 People Missing. Read news below. I wish they will find those people who are missing soon.


Photo from AP.

12 people are missing and seven injured after an explosion and fire at an an ultra-deepwater oil drilling platform off the coast of Louisiana, the Coast Guard said Wednesday.

Most of the 126 people aboard were believed to have escaped safely after the explosion rocked the rig at about 10 p.m. Tuesday, Coast Guard Chief Petty Officer Mike O’Berry said.
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Positive Kick (Wellbore Influx) Indications

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Positive kick (wellbore influx) indications mean signs showing almost 100% kick (wellbore influx) into wellbore.

wellbore influx

Positive Kick Indicators While Drilling

1. Increase in flow show

Without any increasing in flow rate in, increase in return flow indicates something coming into wellbore while drilling. Therefore, flow show instrument provided by the rigs or service companies must be checked and calibrated frequently.

2. Increase of active pit system (Pit gain)

Because drilling fluid system on the rig is a closed system, increasing in flow show without adjusting flow rate in will cause pit gain in a pit system. Nowadays, with high technology sensors, detecting change in pit level is easily accomplished at the rig site. However, visually check the pit level is importance as well for double checking figure from the sensors. Sometimes, change in pit level may be detected after the increase in flow show because it takes more time to accumulate volume enough to be able to detect by pit sensors.

3. Continue flowing while the pumps are off

When pumps are turned off, bottom hole pressure will decrease due to loss of equivalent circulating density (ECD). If there is any flow coming after pumps off, it indicates formation influx into wellbore.

Positive Kick Indicators While Tripping

There are 2 positive kick indicators while tripping as listed below;

1. Trip log deviation such as short fill up while tripping out and excess pit gain while tripping in

For tripping operation, it is very important to have a filling system via trip tank that provides continuous hole fill all time. With utilizing that system, we can compare fluid that is filled in or returned from wellbore with steel volume of tubular (drill pipe, drill collar, BHA, tubing, casing, etc). If drilling fluid volume is less than theoretical pipe displacement while tripping out or more return fluid while running in, you need to flow check and monitor the well.

  • If flow check indicates wellbore influx, crew must quickly shut the well in.
  • If flow check does not show any influx, drill string must be run back to bottom in order to circulate at least bottom up to ensure hole condition.

2. Positive flow when pipe is static

Every time that pipe in static condition. Trip tank with correct filling system must be monitored all time by both rig personnel and mud logger. If volume in trip tank increases, personnel must confirm flow check and prepare to shut the well in.

References

Coleman, S. (2018). Well Control Quiz Online. [online] Well Control Quiz Online – Test Your Well Control Knowledge for Free. Available at: http://wellcontrolquiz.com/ [Accessed 2 Aug. 2018].

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.

Causes of Kick (Wellbore Influx)

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A “Kick” or “Wellbore Influx” is undesirable flow of formation fluid into the wellbore and it happens when formation pressure is more than hydrostatic pressure in wellbore.

Deepwater Horizon offshore drilling unit on fire 2010

Deepwater Horizon offshore drilling unit on fire 2010 (Wiki)

Several causes of Kick (Wellbore Influx) are listed below:

1. Lack of knowledge and experience of personnel (Human error)– Lacking of well-trained personnel can cause well control incident because they don’t have any ideas what can cause well control problem. For example, personnel may accidentally pump lighter fluid into wellbore and if the fluid is light enough, reservoir pressure can overcome hydrostatic pressure.

2. Light density fluid in wellbore – It results in decreasing hydrostatic pressure. There are several reasons that can cause this issue such as

• Light pills, sweep, spacer in hole

• Accidental dilution of drilling fluid

• Gas cut mud

3. Abnormal pressure – If abnormally high pressure zones are over current mud weight in the well, eventually kick will occur.

4. Unable to keep the hole full all the time while drilling and tripping. If hole is not full with drilling fluid, overall hydrostatic pressure will decrease.

5. Severe lost circulation – Due to lost circulation in formation, if  the well could not be kept fully filled all the time, hydrostatic pressure will be decreased.

Lost circulation usually caused when the hydrostatic pressure of drilling fluid exceeds formation pressure. There are several factors that can cause lost circulation such as

• Mud properties – mud weight is too heavy and too viscous.

• High Equivalent Circulating Density

• High surge pressure due to tripping in hole so fast

• Drilling into weak formation strength zone

6. Swabbing causes reducing wellbore hydrostatic pressure.

Swabbing is the condition that happens when anything in a hole such as drill string, logging tool, completion sting, etc is pulled and it brings out decreasing hydrostatic pressure. Anyway, swabbing can be recognized while pulling out of hole by closely monitoring hole fill in trip sheet.

Reference book: Well Control Books

Boyle’s Gas Law and Its Application in Drilling

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Understand Boyle’s Gas Law

Boyle’s gas law states that at constant temperature, the absolute pressure and the volume of a gas are inversely proportional in case of constant temperature within a closed system.  Bolye’s law can be illustrate in the graph shown in figure 1.

Figure 1 – Boyle’s Law

Well, we can describe the statement above into simple mathematics as following formula:

Boyle’s Gas Law

P x V = constant

Or express Boyle’s law in another term:

P1 x V1 = P2 x V2

Where;

P1 = Pressure at condition # 1

 V1 = Volume at condition # 1

P2 = Pressure at condition # 2

 V2 = Volume at condition # 2

Note: You can use any unit for Bolye’s gas law as long as P1 and P2 are the same unit and V1 and V2 are the same unit.

Let’s apply Boyle’s law into our drilling business

Calculate the volume of gas you will have on the surface, 14.7 psi for atmospheric pressure, when 1 bbl of gas kick is circulated out from reservoir where has formation pressure of 3,000 psi. Figure 2 and 3 shows the condition of this well.

Figure 2 – Gas Kick 1st condition at the bottom

Figure 3 – Gas Kick 2nd condition

Apply the Boyle’s Gas Law:

P1 x V1 = P2 x V2

P1= 3000 psi (reservoir pressure)

V1 = 1 bbl (volume at bottom hole)

P2 = 14.7 psi (atmosphere pressure)

V2 = ? (volume at surface)

P1 x V1 = P2 x V2

3000 x 1 = 14.7 x V2

V2 = 204 bbl

Figure 4 – Gas

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.

Let’s apply U-Tube concept

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After learning about U-tube concept, let’s get a example in order to understand clearly about physical meaning of U-tube. This is very important concept so you need to clear about it.

Mud weight inside drill pipe is 9.8 PPG is all the way to bit and mud weight in the annulus is 9.2 PPG all the way to surface. Hole depth is 10,000’MD/8500’TVD. The well is shut in and drill pipe pressure is equal to 0 psi. Determine casing pressure.

According to U-tube concept, both sides (casing and drill pipe) have the same bottom hole pressure so we can write the equation to describe the U-tube concept as shown below;

SP (casing) + HP (casing) = BHP = SP (drill pipe) + HP (drill pipe)

At drill pipe side: BHP = 0 psi (Drill pipe Pressure) + 0.052×9.8×8,500 (Hydrostatic Pressure at drill pipe side) = 4,331 psi

At casing side: BHP = 4,331 psi = (Casing Pressure) + 0.052×9.2×8,500 (Hydrostatic Pressure at casing)

With this relationship (SP (casing) + HP (casing) = BHP = SP (drill pipe) + HP (drill pipe) ),we can solve casing pressure.

4331 = Casing Pressure + 4066

Casing Pressure = 4331 – 4066 = 265 psi

U tube

Ref books: 

Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.