Mfc Control Console

Drilling Equipment Mud Volume
Figure 6.5.2
Driller Console

SECTION 6 : WELL CONTROL EQUIPMENT

To prevent loss of hydrostatic pressure it is necessary to fill the hole on a regular schedule, or continuously, using a trip tank to keep the track of the fluid volume required. The metal volume of the pipe being pulled can be calculated, but mud additions necessary to replace hole seepage losses due to filtration effects can only be predicted by comparison with the mud volumes required to keep the hole properly filled on previous trips. For this reason, it is import that a record of mud volume required, versus number of stands pulled be maintained on the rig in a trip book for every trip made.

Typical Trip Tank Hook-up - On A Floating Rig

As illustrated in Figure 6.5.3, a centrifugal pump takes suction from the trip tank and fills the hole through a line into the bell nipple. The pump runs constantly while the drill string is pulled from the hole. The hole stays full as each stand of pipe is pulled and excess mud returns to the trip tank through an outlet on the main flow line. A valve must be installed in the flow line downstream of this outlet to block all flow to the shale shakers while making a trip. A closed circulation system can be monitored by a float system and a digital read-out in 1-barrel increments on the Driller's console.

Mud Gas Separator

The separator is installed downstream of the choke manifold to separate gas from the drilling fluid. This provides a means of safely venting the gas and returning usable liquid mud to the active system.

There are two types of mud gas separators: Atmospheric and Pressurised.

• The atmospheric type separator is standard equipment on nearly all rigs and is referred to in the field as a 'gas buster' or 'poorboy' separator. The main advantage of this type of separator is its operational simplicity which does not require control valves on either the gas or mud discharge lines.

A pressurised mud gas separator is designed to operate with moderate back pressure, generally 50 psi or less. Pressurised separators are utilised to overcome line pressure losses when an excessive length of vent line is required to safely flare and burn the hazardous gas an extended distance from the rig. The pressurised separator is considered special rig equipment and may not be provided by the contractor. This type of separator is installed on rigs drilling in high risk H^S areas and for drilling underbalanced in areas where high pressure, low volume gas continually feeds into the circulating fluid.

SECTION 6 : WELL CONTROL EQUIPMENT

During well control operations, the main purpose of a mud gas separator is to vent the gas and save the drilling fluid. This is important not only for economic reasons, but also to minimise the risk of circulating out a gas kick without having to shut down to mix additional mud volume. In some situations the amount of mud lost can be critical when surface volume is marginal and on-site mud supplies are limited. When a gas kick is properly shut in and circulated out, the mud gas separator should be capable of saving most of the mud.

There are a number of design features which affect the volume of gas and fluid that the separator can safely handle. For production operations, gas oil separators can be sized and internally designed to efficiently separate gas from the fluid. This is possible because the fluid and gas characteristics are known and design flow rates can be readily established. It is apparent that 'gas busters' for drilling rigs cannot be designed on the same basis since the properties of circulated fluids from gas kicks are unpredictable and a wide range of mixing conditions occur downhole. In addition, mud rheological properties vary widely and have a strong effect on gas environment. For both practical and cost reasons, rig mud gas separators are not designed for maximum possible gas release rates which might be needed; however, they should handle most kicks when recommended shut-in procedures and well control practices are followed. When gas low rates exceed the separator capacity, the flow must be bypassed around the separator directly to the flare line. This will prevent the hazardous situation of blowing the liquid from the bottom of the separator and discharging gas into the mud system.

Figure 6.5.4 illustrates the basic design features for atmospheric mud gas separators. Since most drilling rigs have their own separator designs, the Drilling Supervisor must analyse and compare the contractor's equipment with the recommended design to ensure the essential requirements are met.

The atmospheric type separator operates on the gravity or hydrostatic pressure principle. The essential design features are:

  • Height and diameter of separator.
  • Internal baffle arrangement to assist in additional gas break-out.
  • Diameter and length of gas outlet.
  • A target plate to minimise erosion where inlet mud gas mixture contacts the internal wall of the separator, which provides a method of inspecting plate wear.
  • A U-tube arrangement properly sized to maintain a fluid head in the separator.

SECTION 6 : WELL CONTROL EQUIPMENT

Figure 6.5.3

Offshore Drilling Mud Gas Separator
Figure 6.5.4 An Example Mud Gas Separator

GAS OUTLET 8" ID MINIMUM

^^ GAS BACK PRESSURE ' REGISTERED AT THIS GAUGE - (Typically 0 to 20 psi)

STEEL

TARGET PLATE

INSPECTION ^ COVER

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    How to maintain the drillers console?
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