Put simply, oil and gas extraction
could not exist without the technical drilling fluids and
the myriad additives and minerals that go into them that
are used to simultaneously clean, lubricate and seal
boreholes.
Drilling muds, or fluids, encompass a wide range of products
that each plays a pivotal role in the extraction of
hydrocarbons. Of the three main fluid types water-based,
oil-based, and synthetic water-based fluids consume the
most minerals in their production.

Broadly speaking, this is the chief reason why numerous
industrial minerals rely heavily on oil and gas markets to fuel
demand; the majority of drilling that takes place at present
uses water-based fluids, owing to economic reasons and,
importantly, environmental concerns.
The use of synthetic or oil-based muds, meanwhile, tends to be
reserved for technical wells, where they may be deviated,
horizontal or high temperature.
The engineering behind a drilling fluid is vast: the fluids
must be viscous enough to carry with them cuttings from the
bottom of a borehole, but not be so viscous as to stop cuttings
from settling out in the mud pit.
Sodium bentonite (or swelling bentonite) is one of the primary
minerals that are relied upon to gel with cuttings in the
borehole to ensure they are not re-circulated. Its derived
products are a significant component of drilling fluids along
with other minerals such as barytes.
Along with gel formation, bentonites role is principally
to seal borehole walls and lubricate the cutting
head meaning its consumption is directly linked to oil and
gas exploration, and thus demand.
Bentonites clean sweep?
Consumption of bentonite for oilfield applications accounts for
around 70-80% of the drilling grade bentonite produced, and
around 20% of overall bentonite demand. The mineral has gained
a stronghold in this market owing to its viscosifying
characteristics and effective sealing and filtration
properties.
These properties come from bentonites structure a
colloidal clay comprising mainly montmorillonite meaning
the mineral swells when wet.
Although bentonite is abundant its use in oilfield drilling
means that, similarly to food or pharmaceuticals, stringent
requirements are specified by industry bodies such as the
American Petroleum Institute (API), which often eliminates many
of the potential deposits that could be a drilling bentonite
source (Tables 1-3).
Despite these specifications, the crucial role of bentonite
cannot be denied in this market the mineral has no
substitutes.
Yet for the last decade or so, consumption of bentonite for
well drilling has steadily (albeit gently) declined. The two
reasons behind this appear to be a) recovery of marginal
hydrocarbons, requiring clear fluids; and b) a new
generation of polymers that flocculate formation clays, but
also adversely affect bentonite, itself a clay.
Once a reservoir has been sufficiently drilled and explored,
the transition to a production platform from an exploration
well usually involves replacing water-based muds with clear
drilling fluids. Thus during times of lower exploration but
sustained hydrocarbon production, bentonite-based drilling muds
lose market demand.
However, bentonite-based fluids are still favoured in top hole
sections where they control fluid loss.
Oil outlook
The latest rig counts for October 2010 show significant
improvement on the counts taken 12 months earlier. Major oil
and gas production hubs, such as Canada and the USA, are
pushing increases of up to 60%, while regions less affected by
the downturn are still showing promising rises, such as the
Middle East (see rig count map).
Rig counts, such as those published by oilfield service
providers Baker Hughes and M-I Swaco, are telling barometers
for the drilling industry and its mineral suppliers. At
present, all rig counts are pointing to increased mineral
consumption Ð despite recent temporary bans arising from
the Deepwater Horizon spill in the Gulf of Mexico (IM
November 2010: Oil drilling faces new era of
regulation).
The lack of any clear substitutes for bentonite, and the
promising rig counts currently being reported by the industry,
indicates a comfortable future for bentonite in this market.
However, market production figures for all grades of bentonite
(including drilling grade) have indicated, over the last few
years, a gentle but sustained fall in demand. How these factors
will play out over the longer term is unclear.
Drilling mud basics
Drilling muds, or fluids, can be divided into three primary
types: water-based, oil-based and synthetic. The majority of
fluids used today are water-based, as they are more economical
and environmentally sounder than their counterparts.
Water-based fluids also consume the most minerals in their
production, such as bentonite.
In the well, the role of drilling fluid is to:
- Remove cuttings from the borehole to be stored in a
settling pit
-
Allow cuttings to drop from the fluid into the pit, to
avoid re-circulation
-
Prevent cuttings from settling while drill pipe is
installed
-
Create a layer on the borehole wall to mitigate against
caving, and preserve adjacent formations from being
eroded by the upward flowing drilling fluid
-
Reduce fluid loss by sealing the borehole wall
- Lubricate the drill bit, bearings, mud pump and drill
pipe
Drilling market (land and offshore) October 2010

Hydrocarbon drilling hotspots in October 2010, indicating the
active drilling rig count (land and offshore) and percentage
change from October 2009.
Source: Rig count data courtesy Baker Hughes
Table 1: API specifications - bentonite
Suspension properties |
Standard |
Viscometer dial reading at 600 r/min |
minimum 30 |
Yield point/plastic viscosity ratio |
maximum 3 |
Filtrate volume |
maximum 15cm3 |
Residue of diameter greater than 75µm |
maximum mass fraction 4% |
Table 2: API
specifications - non-treated bentonite
Suspension properties |
Standard |
Yield point/plastic velocity ratio |
maximum 1.5 |
Dispersed plastic velocity |
minimum 10m Pa.S |
Dispersed filtrate volume |
maximum 12.5cm3 |
Table 3: API specifications - OCMA grade
bentonite
Suspension properties |
Standard |
Viscometer dial reading at 600 r/min |
minimum 30 |
Yield point/plastic viscosity ratio |
minimum 6 |
Filtrate volume |
maximum 16cm3 |
Residue of diameter greater than 75µm |
maximum mass fraction 2.5% |
Moisture |
maximum mass fraction 13% |
Source: API