ADC Virtual Academy – Webisode 5 – Circulating System

November 9, 2019 0 By Kody Olson

Welcome to Aberdeen Drilling Consultants Virtual
Academy, the Virtual Academy is an online training environment for the Oil and Gas Industry,
which covers Rig Inspection, Drilling Equipment, Dropped Objects and Level 2 Well Control Training. Welcome to Webisode 5; In this webisode we
will talk about the Circulating System. Drilling fluid, also known as drilling mud
is very important for drilling wells and serves a multitude of purposes. Drilling fluid is used to keep the drill bit
clean, lubricated and cool while drilling. It cleans the wellbore, transports the drilling
cuttings to the surface, prevents the cuttings from falling back to the bottom of the well,
seals the permeable wall of the wellbore when it solidifies to produce a filter cake, helps
to support the drill string. Data loggers use the properties of the mud to monitor the
drilling process using specialised tools. The most important use of drilling mud is
maintaining the primary well control. The hydrostatic pressure exerted by the column
of fluid in the wellbore prevents gas or fluids from entering the well where it could pose
a hazard both inside the well and at the surface. This is achieved by carefully measuring and
adjusting the density of the fluid. Drilling fluid comes in a variety of types
such as synthetic based, oil based and water based. Each type of drilling fluid has different
properties, and with it advantages and disadvantages over other types of fluid. While drilling, fluid is pumped down the well
inside the tubulars and exits through the drill bit, where it collects the drilling cuttings.
The fluid is then returned to the surface up the annulus, transporting the cuttings
up the wellbore. The cuttings are removed as the fluid and cuttings flow over the shale
shakers. The fluid is then returned to the mud pits where it can then be reused. Here
is the full cycle in more detail. Drilling fluid starts out at the mud pits.
The mud pits are a series of tanks where the drilling fluid is stored. During drilling
operations, one or more pits are assigned as the active mud pit. The active pit is monitored to ensure the correct amount of fluid is returning. Chemical checks are
done on the returned fluid, as well as the physical checks to ensure that the density and
viscosity are correct. Using the Active pit gives pit gives a closed system which makes
it easier to monitor. Dry powder gel or other additives can be added
to the mud. There are a number of additives available which change the properties of the
mud. For example barite is added to increase the density of the fluid, to keep
the hydrostatic pressure correct in the well while Bentonite is used to increase the
viscosity of the fluid. The fluid is pumped from the active pit to
the mud pumps at a low pressure using charge pumps. The pinion driveshaft of the mud pump drives
the main bull gear which turns the crankshaft. As the crankshaft rotates, it generates the
linear movement of the crossheads which moves the pistons in and out of the liners. The
suction and discharge valves at the fluid end open and close, allowing the fluid to
be pumped down the well at high pressure. Rigs use multiple mud pumps to achieve the
right pressure and flow. The fluid being pumped by the mud pumps goes
up through the standpipe manifold and down the drill string. Once it reaches the bottom of the drill string it comes out of the jets on the drill bit and moves up the annulus – the area around
the drill string. As it moves up, it holds the drilling cuttings in suspension and carries
them up the annulus. When the fluid reaches the surface, it flows
down the flowline and onto the shale shakers. The shale shakers have vibrating screens;
the fluid flows through the screens the drill cuttings are collected. If the mud is water
based, the cuttings may be discharged overboard. However, if the mud is oil based, the cuttings
are stored in containers to be transported ashore to be processed. It may be necessary for small bubbles of gas
to be removed from the fluid. This is done using a vacuum degasser. The action of the fluid
flowing over the baffle plates of the degasser separates the gas from the fluid. The vacuum
pump then draws the gas out of the unit to be discharged either at the top of the drilling
mast or at a safe distance from the rig. During well control operations, a poorboy
degasser is used as it can handle much larger amounts of gas. The drilling fluid is monitored by the crew
and kept in good condition. If there is too much solids in the mud, it can be removed
by using the desander for coarse solids, desilter for smaller solids and a centrifuge for removing the
finder solids. Once the fluid has been treated, it is returned
to the active mud pit and the cycle starts over. If you would like to find out more about the
content covered within these webisodes, or about the virtual academy, then please contact
Aberdeen Drilling Consultants.