A60 CONTROL CABIN
The A60 control cabin is a pressurized container that consist of the following comparments:
- Control room with HMI operator panel
- MCC room with power distribution to all modules
The mud reserve tanks are provided to store freshly prepared mud until required. The tank is split into two compartments to allow for different mud weights to be prepared and stored. The tank is continuously agitated to maintain adequate mixing and prevent settling of weighting agents.
The fresh mud can be fed from the Pill/Slug tanks to any of the mud reserve tanks using either of the pill/slug tank transfer pumps to allow maximum flexibility.
The contents of the mud reserve tankt can be routed to the rig system, mud disposal system, Pill & Slug tanks, Trip tank ad to the active tank.
ACTIVE AND TRIP TANK
Active tank is split internally using over and under flows into the following sections:
- Sand Pit – After the drilling fluid passes through the shale shaker, it enters the active tank system. Large sand-size particles will settle and are removed from the active tank system via the Mud Tank Draw Pump. The bottom of the sand trap is sloped to the frain nozzle to facilitate quick dumping and aid solids removal. The sand trap will not be agitated and should overflow into the next compartment.
- Degasser Suction Pit – For proper operation of vacuum degasser, the suction pit is the first pit after the sand trap. An underflow is present between the degasser suction pit and the active pit in order to maximise active tank volume, allowing the vacuum degasser to operate at its duty point and provide degassed fluids for the mud pumps. The bottom the the degasser suction pit is sloped to the frain nozzle to facilitate quick dumping and aid solids removal. the degasser suction pit will not be agitated.
- Active pit – The active pit is where the vacuum degasser discharges the degassed fluid, the cetrifuge inlet/outlet connections and provides a constant fluid supply for the mud booster pumps. The bottom of the active pit is sloped to facilitate quick dumping. A sloped bottom will self-clean when dumped. The active pit will be agitated.
Trip tank is a separate compartment of the active tank module. It has a liquid-level gauge to measure the volume of drilling fluid entering or leave the tank. The volume of fluid that replaces the volume of drill string is normally monitored on trips to make certain that formation fluids are not entering the well bore. When 1 m3 of steel (drill string) is removed from the borehole, 1 m3 of drilling fluid should replace it to maintain a constant liquid level i the well bore. It the drill string volume is not replaced, the liquid level may drop low enough to permit formation fluid to enter the well bore due to the drop of hydrostatic pressure. This is known as a kick. Fluids may be returned to the trip tank during the trip into the well when the drill string is returned to the bottom of the well bore. The excess fluid from the trip tank should be returned to the active system across the shale shakers. Large solids can come out of the well and plug the active system of the drilling fluid bypasses the shakers. The addition of trip tanks to drilling rigs significantly reduces the number of induced well kicks.
MUD MIX MODULE
The mud mix module is a container that’s contain equipment to add solid chemical in a safe and convenient way. The mud mix module consist of following components / functions:
- Lifting table – Loading platform give access to add pallets with sacks of solid chemicals. The lifting tales function is to lift the pallet up to working height for the vacuum lifter.
- Vacuum lifting unit – Vacuum lifting unit it used by operator to lift and move sacks from lifting table to sack dosing unit.
- Sack dosing unit – Sack dosing unit open the sacks and dosing the solid chemicals into the mud flow in a dust free and safe way. Dosing rate is selected at SDU monitor.
PILL AND SLUG TANK
Pill & Slug module have two small compartments of 10 m3 each and form part of the mud mix treatment system. These compartments are isolated from the active system and are available for small volumes of specialized fluid.
They are manifolded to the Mud Mixing Module so that solid chemicals are added and are used to create the proper mud consistence and rheology to suit down the hole requirements.
Two centrifugal pumps of the mud shear type with suction lines from both tanks is connected with a combination of fixed piping and flexible hoses to both reserve tanks skids and to the active tanks.
Frame weight – 5 000 kg
Gross weight – 20 000 kg
Tank capacity – 2 x 10 m3
Design pressure – 19,6 barg
Operating pressure – 5,5 to 8,13 barg
MUD GAS SEPARATOR
The Mud Gas Separator receives drilling fluid from the choke valve skid. The purpose of the Mud Gas Separator is to remove gas mixed with the drilling fluid before the drilling fluid flows over the shale shaker. The mud entering the inlet spins, and the centrifugal force allows the gas to go the center and out while the mud goes to the sides and down. A pipe on the top routes the gas to flare. A pipe on the bottom is open to the Shale Shaker feed pod. The Mud Gas Separator is fitted with a pressure gauge and a pressure transmitter, both calibrated from 0 – 1 barg, and level gauge. Monitoring of these devices will ensure the maximum pressure is not exceeded thereby preventing gas blow by to the shale shaker and also prevent overfilling of the mud gas separator.
The mud discharge line contains a U-tube to prevent gas blow by to the shale shaker in the event of an increase in vent backpressure during a kick. The U-tube seal also maintains a liquid level in the separator ensuring sufficient residence time for separation.
The ventline is mounted on top of the mud gas separator.
- Frame height: 4,50 m
- Size of foot: 2,512 x 2,506 m
- Weight of unit: 1700 kg
The shale shaker is an electrically driven balanced elliptical vibrating machine. Two vibratory motors are mounted on the Shale Shaker. It has triple deck screen arrangement, with individual screen pneumatically clamped in place.
The recovered fluid will be collected, under gravity, within the sand trap section of the active tank. Solids will be conveyed to the end of the shaker and fall into the Shale Shaker Disposal Package.
SHALE SHAKER FEED BOX
Shale Shaker Feed Pod (Headerbox) The Shale Shaker Feed Pod is provided to hold well fluids prior to separation over the Shale Shaker. The Feed pod also allows for magnets to be installed to remove/analyse any metal particles recovered. The header box has a knife gate valve which allows the well fluids to enter the Shale Shaker.
The Shale Shaker Feed Pod receives well fluids either from above via the Mud Gas Separator or directly from the well via a common inlet line. A second inlet line is present to allow any section of the Active Tank, or Trip Mud Tank to be routed to the Shale Shaker by using the Mud Tank Draw pump.
Shale Shaker Extraction Hood (HVAC)
High concentrations of gas are expected in and around the Shale Shaker. Especially above the shaker bed, as this is the first place where returned fluids become exposed to atmosphere (only if the Mud Gas Separator is bypassed). To minimize the risk to personnel, and extraction system is used. A roof mounted HVAC is used to draw gas and air from the surrounding area and is routed to a safe location.
The mud discharge line contains a U-tube to prevent gas blow by to the shale shaker in the event of an increase in vent backpressure during a kick. The U-tube seal also maintains a liquid level in the separator ensuring sufficient residence time for separation. A minimum mud density of 1200 kg/m3 will be used to size the height of the U-tube (the minimum mud density will yield the greatest U-tube height)
The vacuum degasser is a hydraulically driven machine which is installed above the active tank.
The drilling fluid is drawn up from the pits by a vacuum which is created from a regenerative vacuum blower on the top of the unit. The drilling fluid enters the vacuum chambers of the unit through holes in the top of the central rotating pipe and is accelerated further and sprayed outwards against the wall of the vacuum chamber. The gas is pulled to the vacuum pump through a narrow gap at the upper edge of the vacuum chamber which prevents liquid entrainment. The pressurized gas is then routed to a safe area via a dedicated pipeline.
The drilling fluid drains to the bottom of the vacuum chamber where it is picked up by an evacuation pump and discharged into the next chamber of the active tank.
The system is controlled by a buoyant scheduling ring in the vacuum chamber that controls the height of the liquid in the vacuum chamber by restricting of opening the entrance to the vacuum chamber.
The centrifuge is used to reduce and discharge fine solids within the active mud system. This recovers the more expensive liquid phase of the mud for reuse, minimising dilution and therefore reducing mud cost. The centrifuge will be used when there is a noticeable increase in the mud weight and further solids removal is required.
The centrifuge is installed over the final section of the active tank, after the drilling fluid has been degassed and processes 10-15% of the circulating volume. The unit uses a rotating central bowl which draws the fluids inside and through centrifugal force expels the heavier solid particles to the outside of the bowl wall. The heavy particles are then scraped towards the solids discharge port by a conveyor. The lighter liquid particle overflow can then be discharged back into the active tank while the solids underflow is discharged into the disposal package.