- Home
- Categories
- Drilling Fluid Systems
- Mud Mixing and Storage
Drilling Operations
Mud Mixing and Storage
Mud mixing and storage covers the equipment that builds drilling mud and holds it in the pit system. This Category includes portable mud tanks and skid-mounted pit modules, agitators, mud guns, mixing hoppers, shearing units and the centrifugal pumps that transfer, mix and charge mud between pits.
How the pit system works
The pit room holds active, reserve and pill pits, and often a dedicated mixing pit. Dry barite and bentonite arrive pneumatically from bulk tanks into surge tanks above the hoppers. Liquid additives and sacks go in at the hopper. Centrifugal pumps drive mud through a venturi nozzle in each hopper, and the low pressure at the throat draws in powder and wets it.
Agitators keep weighting material and solids in suspension, and mud guns jet mud along the pit floor to stop settling in corners. Shearing units apply high shear to new polymer and clay mud so it hydrates faster. Transfer pumps move mud between pits and to the charge side of the mud pumps.
Configurations
- Agitators. A motor drives a right-angle gearbox, often helical-bevel or worm type, on top of the pit. The shaft carries one impeller, or two on deep pits. Canted-blade impellers push flow axially and suit suspension. Flat-blade impellers give more radial shear.
- Hoppers. Standard venturi hoppers mix powder. High-shear hoppers and dedicated shearing units speed polymer hydration. Bulk bag and sack-cutting units reduce manual handling.
- Pumps. Centrifugal pumps are named by suction size, discharge size and impeller diameter in inches, such as 6x5x14. Seals are packing or mechanical.
- Tanks. Pits built into the hull belong to the unit. Portable tanks and skid pit modules can move between rigs.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Agitator power | Must suspend solids for the pit size and mud weight | hp (kW) |
| Impeller type and diameter | Set flow pattern and turnover rate | canted or flat blade, in (mm) |
| Gearbox output speed | Sets impeller tip speed | rpm |
| Pump size and impeller | Set flow and head | suction x discharge x impeller, in |
| Pit or tank volume | Sets working capacity | bbl (m³) |
Standards and certification
Little of this equipment holds pressure, so few API product specifications apply. Under the IMO MODU Code and IEC 61892-7, an enclosed pit room downstream of the final degassing point is usually Zone 2, and pits where gas can collect may be Zone 1. Agitator and pump motors need IEC 60079 or ATEX certificates for the zone on the rig's hazardous area drawing. A portable tank or skid lifted offshore needs certification as an offshore container or portable offshore unit, typically to DNV-ST-E271 (formerly 2.7-1) or DNV-ST-E273 (formerly 2.7-3), with a certified lifting set. Pits built into the hull fall under the unit's class rules for tank structure.
Failure modes and inspection
- Agitator gearboxes. Check oil condition, bearing noise, seal leaks and backlash. Measure shaft runout at the impeller end.
- Impellers. Blades erode at the tips and lose diameter. Measure them against the original size.
- Centrifugal pumps. Impellers, casings and wear plates erode. Measure casing wall thickness and check the mechanical seal or packing gland.
- Hoppers and mud guns. Venturi nozzles wear and lose suction. Check nozzle bore against the original size.
- Tanks. Ultrasonic thickness readings on floors, sumps and around nozzles find corrosion that a visual survey misses. Check coating and internal baffles.
- Lifting points. Padeyes need a current magnetic particle or dye penetrant inspection and a valid lifting certificate.
Documentation
Ask for motor nameplates and Ex certificates, gearbox model and ratio, impeller drawings, pump curves, tank drawings with compartment volumes, and for portable units the container certificate, lifting set certificate and the last periodic inspection report.
Integration and compatibility
An agitator shaft length must suit your pit depth and its mounting beam must suit the pit top. Impeller size depends on the pit's volume and shape, so a used agitator moved to a different pit may need a new impeller. Check pump flange sizes and ratings, motor voltage and frequency, and how the pit levels connect to tank and volume monitoring sensors.
Refurbishment and recertification
Agitators and centrifugal pumps rebuild well, since gearboxes, seals, impellers and wet ends are replaceable. A portable tank returns to service after thickness checks, coating repair, a padeye inspection and renewal of its container certificate. Unused surplus agitators and pumps often come from newbuild spares packages and need only a check of seals and gearbox oil. Dry barite and cement come from bulk storage tanks, so match hopper capacity to the bulk delivery rate. NOV builds agitators under the Brandt name and centrifugal pumps under its Mission name.
FAQ
Frequently asked questions
How do I size a mud agitator for a used mud tank?
Size the agitator to the compartment's volume and shape, the mud weight and the pit's job. Mixing and pill pits need more shear than storage pits. Give the OEM the tank dimensions, the mud weight and the duty, because impeller type, diameter, gearbox speed and shaft length all follow from them.
What does a mud shearing unit do?
A shearing unit applies high shear to new mud so polymers and clays hydrate faster and reach their design properties sooner. It usually pairs a centrifugal pump with a shear hopper or a shear nozzle, recirculating mud through a hydration tank until it is ready.
Can used offshore mud tanks be moved to another rig?
Portable tanks and skid-mounted pit modules can be moved, but pits built into the hull cannot. For a portable unit, check wall thickness, coating, nozzle positions, its offshore container certificate and the lifting set. Confirm the full weight with mud suits the deck load where it will sit.
What certificate does a portable mud tank need to be lifted offshore?
A portable mud tank lifted offshore needs certification as an offshore container or portable offshore unit, typically to DNV-ST-E271 or DNV-ST-E273, with a certified lifting set. Check that the certificate is current and that the periodic inspection of padeyes and lifting gear is in date.
Can a worn centrifugal mud pump be rebuilt?
Yes, most centrifugal mud pumps rebuild with a new impeller, casing or wear plates, shaft sleeve and seal. Measure casing wall thickness first, because a casing worn below the OEM limit should be replaced. Confirm the pump size and impeller diameter still suit the head and flow you need.
Looking for mud mixing and storage?
Tell us what you need and we will find out what is available. We reply within one business day.