Drilling muds, or drilling fluids,
are an integral part of the drilling process. These specialised
fluids, which contain minerals such as bentonite, barite,
calcium carbonate and graphite, are used to help in the process
of drilling a borehole into the earth, which are created for
oil and gas extraction, as well as a variety of other reasons.
The various minerals added to drilling mud enable it to
lubricate the drill bit and bring the drill cuttings up to the
surface. Drill cuttings are bits of solid material that are
created as the drill bit breaks the rock, and when these come
up to the surface, the mud and cuttings are separated.
On completion of the drilling
process, drilling mud must be disposed of, and one such cost
effective method is the recycling of drilling waste, which can
also help to reduce a companys environmental
Drilling mud properties
Drilling muds have a continuous
liquid phase and are modified with various liquid and solid
chemical additives to suit the performance of the fluid to
drilling conditions. These fluids are usually a mixture of
water, clay, weighting material and chemicals, and provide a
way of keeping the underground pressures in checkÑthe
denser the fluid, the more pressure it exerts.
Weighting materials, usually
barite, are added to the drilling mud to help it exert as much
pressure as is required to contain the pressures of the
There are three types of drilling
muds: water-based mud (WBM), oil-based mud (OBM) and
synthetic-based mud (SBM).
WBMs begin with water, then clays
and other chemicals are added to create a homogenous blend.
Clay, or shale, is generally a mixture of native clays
suspended in the mud during the drilling process. The most
common of these clays is bentonite, which is often called
Numerous other chemicals are added
to the water-based system to achieve a variety of effects, such
as viscosity control, shale stability, cooling and lubricating
of equipment. WBMs consist of bentonite clay with additives
such as barium sulfate, calcium carbonate (chalk) or hematite.
Thickeners, such as xanthan gum, glycol and starch, are also
often used to influence viscosity.
OBMs consist of a base fluid made
up of a petroleum product, such as diesel fuel. They are often
used for increased lubricity, enhanced shale inhibition and
greater cleaning abilities with less viscosity than WBMs. These
fluids are composed of oil as the continuous phase, and water
as the dispersed phase, along with emulsifiers, wetting agents
and gellants. OBMs are capable of withstanding greater heat
without breaking down.
SMBs, also known as low toxicity
oil based mud (LTOBM) have a base fluid of synthetic oil. These
fluids are most often used on offshore rigs because they have
the same properties as OBMs but a toxicity of fluid fumes that
is much lower.
After the drilling process is
finished, the drilling waste must be disposed of in some
Drilling mud recovery
However, both drilling mud and
drill cuttings contain traces of hydrocarbons, which can be
hazardous to the environment. Fortunately, waste streams that
are especially high in hydrocarbons, such as oil-based muds,
are ideal candidates for thermal treatment technologies.
Through processes like thermal desorption, hydrocarbons can be
recovered from drilling muds, which can then be beneficially
Recovering drill cuttings and
drilling fluids is both practical and cost-effective, as well
as an environmentally-sustainable process. Recycling drilling
waste not only helps companies save money on disposal costs,
but can reduce truck traffic and thus a companys
Recovered drill cuttings can be
utilised to stabilise surfaces that are more vulnerable to
erosion, such as roads and drilling pads. Cuttings also have a
use as aggregate or filler in concrete, brick or block
manufacturing. Some studies have even been done on the
potential of using drill cuttings as a substrate for restoring
coastal wetlands or as fuel for power plants.
Worldwide Recycling Equipment
Sales, LLC in Moberly, Missouri, US, is one company which can
supply a full range of equipment for thermal desorption
processes. Its systems can be custom-designed specifically to
suit individual project needs, with previously designed thermal
desorption systems capable of processing up to 10 tonnes
material per hour.
The companys new Vulcan IDR
8440 is a 40 inch long x 7 inch diameter COR-TEN indirect
heated rotary thermal desorption unit. This system is designed
to remediate soils and drilling muds contaminated with
The Vulcan IDR 8440 comes equipped
with a vapor recovery unit (VRU) to capture vapors from the
Primary Thermal Desorption Unit (PTU). According to Worldwide
Recycling Equipment Sales, the system is capable of recovering
drill cuttings of up to 100 MMBtu per hour of energy for reuse
as fuel, reducing the total operating cost and improving total
return from projects.
In the Vulcan IDR 8440, material is
fed to the feed hopper, which is mounted on a pugmill and
equipped with a weight-controlled feed valve. From the pugmill,
the material is transferred via a transfer auger to the feed
auger, which conveys the material into the PTU and maintains a
seal or airlock for the system.
The indirect fired rotary kiln
has four heat zones, and the operating temperature of the
drum can reach 1,000 degrees Fahrenheit. The kiln operates in
an oxygen-deficient environment and under a slightly negative
Vapours from the contaminated
material are pulled out of the system in a countercurrent
direction to the material flow. The clean, dried material is
charged to a water-cooled discharge auger that rehydrates and
cools the soil. The steam is then extracted through a quench
stack that removes any particulate from the H2O
vapour stream before discharging it into the atmosphere.
Recycling drill cuttings and
drilling muds can help operators meet disposal regulations, and
the proper disposal of such waste prevents the contamination of
water supplies and the soil, Worldwide Recycling Equipment
Sales said. Through this process, muds and cuttings may be
reused, saving money and contributing to the health of the
Vulcan Systems custom-designs and manufactures drying,
calcining and thermal desorption equipment. Each system is
custom-built to suit the clients specific needs. The
companys services include setup, commissioning, training
and maintenance support services over the lifetime of a