Possible Wellbore Problems during Well Kill Operation

In the previous article, Common Problems and Complications During Well Kill Operation, it is about commons complications that can be possibly seen while performing well control operation. For this article, it will discuss other wellbore problems which are stuck pipe, surface pressure reaching to MAASP, lost of control and hydrate.

Stuck Pipe

During a well control operation, a stuck pipe can occur and this has the potential to lead to serious issues. Whenever the pipe is off bottom, the chances of the pipe getting stuck increases. Therefore, rotating the pipe should reduce the risk of this problem occurring. However, with the well shut it, it is impossible to rotate to minimize stuck pipe so the stuck pipe should be dealt after the well is properly secured.

Throughout well control operation, wellbore pressures will be high and this means the most common cause of a stuck pipe comes from differential sticking. However, this isn’t to say mechanical sticking can’t occur if the hole sloughs and packs-off after coming into contact with the influx fluids.

Operation can normally continue when the pipe is differentially stuck (with the bit on bottom) because the well can still be killed with circulation. Once the well is killed, then the pipe can be free safely later.

When the bit is off bottom and the pipe becomes differentially stuck, this is a more complicated scenario since it’s more difficult to reduce wellbore pressure; at that depth, it’s normally impossible to achieve a reduction by circulation. Although there may be opportunities to spot a freeing agent and free the pipe, volumetric control is the chosen method if the influx was swabbed in.

When the pipe is mechanically stuck, the pipe can be freed by spotting a freeing agent and working the pipe (by combining the two, the desired result is achievable!).

Stuck Pipe due to Differential Sticking

Figure 1 – Stuck Pipe due to Differential Sticking

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What’s a Poor Boy Degasser (Mud Gas Separator)?

Poor Boy Degasser or Mud Gas Seperator, located downstream of the choke manifold, is a vertical vessel used to separate any gas from drilling fluid during well control situation. Once the gas has been separated, it can pass through the vent line in the derrick. Alternatively, as long as it’s a safe distance from the rig, it could even be vented.

Figure 1 - Poor Boy Degasser (Courtesy of H-Screening)

Figure 1 – Poor Boy Degasser (Courtesy of H-Screening)

With mud’s separators, there are two main types. Also known as a ‘poor-boy’ and a ‘gas buster’, the more common of the two is called an atmospheric mud/gas separator. However, some mud/gas separators are designed to operate at moderate back pressure. Although these will mostly operate under 100 psig, it’s possible to come across those that work at the atmospheric gas vent line pressure plus the vent line friction drop. The simple diagram of poor boy degasser is show in figure 2.

mud-gas-seperator-1

Figure 2 – Poor Boy Degasser (Mud Gas Separator) Diagram Continue reading

What is a degasser on a drilling rig?

A degasser is equipment used to remove entrained gas in drilling fluid so it prevent or minimize reduction of hydrostatic pressure due to gas cut mud. When drilling mud passing over the shale shakers while drilling, gas will normally be released. However, the wellbore could receive additional volumes of gas and these need to be removed from the mud. If not removed from the circulating system properly, recirculation of mud containing gas will reduce the well’s hydrostatic head. With a degasser, this can eliminate or minimize loss of hydrostatic pressure.

Figure 1 - Degasser (Courtesy of NOV)

Figure 1 – Degasser (Courtesy of NOV)

Mounted over the active pit, degassers are essentially a one-stage liquid/gas separator. With a maximum lift to the inlet of around ten feet, mud vacates the submerged pipework in the mud pit and enters the degasser. From here, a three hp electric motor will power a vacuum pump and this should be mounted atop the degasser itself. By the pump, the vacuum is then applied to the vapor space.

Ultimately, the range applied by the vacuum will depend on the density of the mud passing through. In most cases, it will offer between 2-5 pounds per square inch (between 8 and 15 inches of mercury). In terms of extracting gas from mud flows, 900 gallons per minute is likely to be the maximum rate. Continue reading

Common Problems and Complications During Well Kill Operation

During well kill operation, crews should always be vigilant since complications can actually occur at any stage. If there’s a discrepancy in the kill plan, it needs to be noted immediately. For example, pressure gauges may stop working; they therefore should be monitored carefully. If there’s a failure, back-up gauges need to be made available during a well control operation.

In this article, it will describe common problems and complications during well kill operation which are plugged bit nozzle, plugged choke, choke washout, pump failure and string washout.

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Possible Kick Indicators in Well Control

The alertness in determining early possible kick indicators in well control is of the utmost importance to prevent a well control incident. Careful observance and positive reaction to these signs will keep the well under control and prevent the occurrence of a well control situation.

The various signs that have been recorded as early warning indicators are not consistent in all situations. The signs however may have to be used collectively as one indicator may not accurately provide the warning of getting into an underbalanced situation. Even though the series of signs may change between wells, early warning indications can be found from the following list.

  • Increase in drilling rate of penetration.
  • Increase torque and drag.
  • Decrease in shale density.
  • Mud property changes.
  • Increase in cutting size and shape.
  • Increase in trip, connection and/or background gas.
  • Increase in the temperature of the return drilling mud.
  • Decrease in D-exponent.

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