The drilling mud circulating system components comprises the following equipment:
- Active Tank(s)
- Reserve Tanks
- Sand Traps and Process Pits
- Slug and Pill Tanks
- Trip Tank & Stripping operation Tank
- SCE (Solids Control Equipment)
- Mixing System
This is the tank from which drilling fluid is pumped downhole and to which drilling fluid returns from the hole are received. The route taken by the drilling fluid when circulating is called the active (circulating) system. At the start of circulation, the Mud Pumps are lined up on the Active Tank and drilling fluid is pumped to the Stand Pipe Manifold on the drill floor. The drilling fluid then travels up the Stand Pipe and Kelly Hose to the Swivel or top drive in drilling rig (TDS), both of which suspend the drill string and allow it to rotate independently from the Kelly Hose. Overhead View of Mud Tanks and Mud Pumps. From there, the drilling fluid travels down the drill string to the drill bit, where it picks up drilled cuttings and carries them up the annulus between the drill string and the well bore. A Bell Nipple underneath the drill floor sends the drilling fluid returns from the hole along a flow line that leads to the Scalping Shaker and Shale Shakers, which remove most of the drilled cuttings. The drilling fluid then passes through the Sand Traps and Process Pits, which contain additional Solids Control Equipment to remove smaller-sized solids in the drilling fluid. The cleaned-up mud then flows back to the Active Tank to complete the circulating system.
These are used for storing fluids according to requirements. Reserve mud is usually prepared or stored in these tanks, or different fluids in preparation for the next phase (e.g. oil-based mud or completion brine).
Sand Traps and Process Tanks In Drilling circulating system
The Sand Traps are usually positioned below the shale-shakers and act as settling pits for the drilling fluid after passing through the shale-shakers. The drilling fluid then passes through the Process Tanks, comprising degasser, desander, desilter, and centrifuge tanks. As the names suggest, these tanks contain degassers along with solids control equipment for removing smaller-sized particles from the drilling fluid before being returned to the active tank.
Slug and Pill Tanks
These tanks are smaller than the active and reserve tanks and are used for preparing “slugs” (high density mud that is pumped into the drill string before tripping out of the hole) and pills to address particular situations (e.g. an LCM pill to control formation losses, a special mix to improve drilling mud properties, etc.).
Trip Tank and Stripping Tank
The Trip Tank is a tall, narrow tank that is located near the flow line and used for monitoring drill pipe displacement volumes accurately while tripping pipe in or out of the hole. Active drilling fluid from the Trip Tank is circulated across the hole and valves in the flow line near the Bell Nipple are realigned to send the fluid returns back to the Trip Tank, forming a very small circulating system. Pipe displacement causes the Trip Tank to fill up when running in hole (RIH), and to empty when pulling out of the hole (POH), so it needs to be emptied or filled at regular intervals while tripping. The Stripping Tank is smaller than the Trip Tank and is used for monitoring pipe displacement volumes when stripping in or out of the hole when the Annular Bag Diverter is closed.
SCE (Drilling Solids Control Equipment) In Circulating system
It is important to minimize the build-up of solids in a drilling fluid because they affect drilling performance and can encourage hole problems. A range of equipment is available for removing solids from the drilling fluid, some or all of it found in the following order: Scalping Shaker, Shale-Shakers, Desander, Desilter, Mud Cleaner, and Centrifuges.
The mixing system is used for building and treating drilling fluids, and for preparing slugs and pills. Equipment includes centrifugal pumps and mix hoppers, and may include pressurized surge tanks for adding bulk Bentonite or Barite. Fluids can usually be mixed in any of the active, reserve, slug and pill tanks. The mix pumps are also used for transferring fluids to other parts of the rig (e.g. to the trip tank, cement unit, sand traps, etc.), or for back loading fluids to a road tanker or supply boat.