Drilling Fluids: Presence of Hazardous BTEXs and Crystalline Silica

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1029-1035

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Drilling Fluids: Presence of Hazardous BTEXs and

Crystalline Silica

Lakmun Chan , Nithiya Arumugam , Sathiabama T. Thirugnana and Shreeshivadasan

Chelliapan²

Razak Faculty of Technology and Informatics, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia

Department of Engineering, Razak Faculty of Technology and Informatics, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur,

Malaysia

Ocean Thermal Energy Conversion (OTEC), Razak Faculty of Technology and Informatics, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra,

4100 Kuala Lumpur, Malaysia

Received: 25/03/2020

Accepted: 26/06/2020

Published: 20/09/2020

Abstract

In the oil and gas industry occupational health risks due to drilling fluids is severe. Mixing room, shale shaker room and drill floor are

sites where workers are highly exposed to air pollutants, hazardous dust and even substances generated via drilling fluids associated activities.

Barite, calcium carbonate and linear paraffin or olefin-based oil are three types of chemical that are greatly used in huge quantities to prepare

drilling fluids. These drilling fluids contain hazardous substances and pose health risks. Due to the occupational health risk, Occupational

Safety and Health Administration OSHA Europe and USA have issued guidelines for the permissible exposure limit (PEL) to be at 5 mg/m

for barium sulphate, 10 mg/m for calcium carbonate, 0.05 mg/m for crystalline silica and 0.05 mg/m for oil mists. Therefore, this study

identified the presence of benzene, toluene, ethylbenzene and xylene (BTEX) ionic mists and crystalline silica in the drilling fluids. The grain

size distribution of additives used in the drilling fluids was also determined. The results showed the presence of BTEX and crystalline silica

based on random sampling. Therefore, the existing control measures are necessary to reduce the occupational health risks. As a control

measure, Artificial Intelligence (AI) and Internet of Things (IoT) are necessary to be introduced for the automation of drilling fluids associated

activities.

Keywords: Drilling fluids; Occupation health risk; Hazardous; BTEX; Barium sulphate

Introduction¹

the drill hole via a mud pump and a discharge line. These drilling

fluids are circulated down the drill string and then out through the

bit. The drilling fluids are moved back up to the annulus and

straight into the surface. The huge quantities of drill cuttings are

composed of rocks and particulate mixtures which are released

from geological formations generated during the drilling

operation (5). Cuttings that are suspended from the hole by

drilling fluids are unwanted and removed when they flow through

the shale shaker (4). The above-mentioned drilling fluids flow

cycle is illustrated in Figure 1.

The selection of drilling fluids solely depends on their

behaviours during the operation despite their drawbacks due to

environmental concerns. The drilling fluids cycle will happen at

elevated temperature together with agitation. This potentially

exposes chemicals as well as oil vapour/mists; subsequently,

affecting the health of workers both in short-term and long-term

Drilling fluids have a vital role in measuring the success rate

of drilling operations. These fluids are important to increase the

oil recovery and shorten recovery time (1). Commonly used

drilling fluids in the oil and gas industry are water-based, oil-

based and synthetic-based muds (2). Drilling operation has three

simultaneous systems that work in a boring hole. The first is a

rotating system while second is a lifting system. The thirdsystem

is a circulating system. The rotating system rotates the drill bit

while the lifting system is used to lift up and lift down the drill

string into the hole. The circulating system will circulate fluids

around from the drill stem, out of the drill bit and up again into

the hole at the surface.

The drilling fluids are often used to eliminate cuttings from

the drilling hole, transport them to the surface and are also used

as a stabiliser and supporter to the wellbore (3). Besides, the

drilling fluids help to cool and lubricate the drill bit (4).

Preparation of drilling fluids starts at the mud mixing hopper. The

mixing hopper performs as a chemical mixing station and then the

fluids are retained in the mud pits/tanks before being pumped into

(6). Comprehensive risk assessments of drilling fluid systems

need to be conducted by the operator well planners, taking into

consideration the aspects of health, environment and safety when

deciding on the type of drilling fluids to be used for the system.

Corresponding author: Nithiya Arumugam, Department of Engineering, Razak Faculty of Technology and Informatics, Universiti

Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia. E-mail: nithiya85.a@gmail.com.

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2020, Volume 8, Issue 3, Pages: 1029-1035

The outcomes of these assessments should be made accessible to

all employees who may be exposed to the system.

Figure 1: The drilling fluids recirculation and preparation

As highlighted in Figure 1, workers working in these three

areas (drilling floor, shale shaker, chemical mixing station and

mud pits/tanks) are highly exposed to hydrocarbons and oil mists

that work-related illnesses may only be visible after a few years

of exposure to toxic substances (8). Long-term exposure to barite

(barium sulphate) in drilling fluids and oil mist/vapour may cause

lung diseases (9). Drill cuttings are usually characterised by high

content of polycyclic aromatic hydrocarbons (PAHs), which is

potentially carcinogenic or mutagenic to mammals and aquatic

organisms (10). Chen et al. (11) assessed the inhalator and dermal

exposures to PAHs in oil mists and their consequential risks of

cancer, specifically lung and skin, with regard to health-risk

management. However, very few studies were carried out on oil

well drilling workers’ exposure hazards (7,12–14).

The basic three components in drilling fluids that are used in

large quantities are barite, calcium carbonate and linear paraffin-

based oil. The vapour of non-aqueous drilling fluids consists of

low-boiling point portion of hydrocarbons, while the mist consists

droplets of the hydrocarbon portion. Although these hydrocarbon

fractions may contain insignificant amount of known toxic

components like benzene, toluene, ethylbenzene and xylene.

They are collectively referred as BTEX, which will evaporate

relatively faster, resulting in vapour with higher concentration

than the estimated. Exposure to BTEX is correlated with health

risks and may cause neurological effects,which is generally to the

(7). At the shale shaker, they are possibly exposed by inhaling

aerosols and vapour/mists or through dermal contact. Dermal

contact predominantly occurs with drilling fluids, lubricants,

hydraulic oils and other personnel at the drilling floor. At the

chemical mixing station and mud pits/tanks, workers are greatly

exposed to burns, or physical injuries due to dermal or eye

contact. Potential inhalation risk and explosions or aggressive

reactions from improper chemical mixing are also greatly

possible in these areas.

Skin irritation and skin diseases are the prevalent short-term

health hazards observed when working with drilling fluids (7).

Physicochemical properties of the drilling fluids, together with

the inherent properties of the drilling fluid additives, are the root

cause of these problems and are reliant on the exposure route,

either through dermal absorption, inhalation or orally. There are

concerns about the break down of organic components or even

occurrence of chemical reactions which will produce more toxic

components due to the operation of drilling fluids in an open

system at elevated temperature and pressure (6). There are facts

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2020, Volume 8, Issue 3, Pages: 1029-1035

central nervous system depression via the oral route, as well as

renal and hepatic effects (7,15–17).

of analytical methods used in this paper are discussed in

subsequent sections.

Barite is one of the most important components in drilling

mud with its principal use as a weighting agent. It is used in

substantial tonnages to increase the density of drilling mud due to

its high specific gravity, balancing formation pressure and

preventing a blowout (18–20). Barite used combinely with other

substances like calcium carbonate to produce mud. This mud will

be pumped down into the drill hole to control the high pressure

formation and avoid explosive discharges of oil and gas from the

well. The soft characteristic of barite prevents the drilling

equipment from becoming worn. Besides, it is nonmagnetic and

does not interfere with the logging drill holes’ instrumentation.

Basically, the usage of barite in drill hole differs significantly

from site to site and depends on factors, such as hole depth and

diameter, rocks types and drilling conditions like fractures and

hole pressure (21).

Analytical Methods

a) Gastec® Gas Sampling System

The Gastec® gas sampling system was used to check the level

of BTEX in various locations at the drilling rig. These

conventional Gastec tubes used colorimetric technology ,whereby

the chemical reagent in the gas tube reacted with the gas sample

as it was drawn towards the tube via a pump. Detector tubes were

specified according to types of gas to be measured, as shown in

Table 1. The length of colour stains produced was proportional to

the concentration of gas. The concentration may be read

immediately by using the calibration scale printed on the tube.

b) X-ray Diffraction (XRD)

Barite powder was compacted in the sample holder and

placed in the PANalytical XRD Machine for analysis. The XRD

patterns were documented with Cu Kα-radiation (λ=1.5406 Å).

The 2θ values were scanned from 10º to 70º with 45kV and at a

scan speed of 2º/min at 25ºC.

Silica consists of silicon and oxygen in the form of silicon

dioxide (SiO ) and is found abundantly on Earth. It exists either

in a crystalline or non-crystalline form. Crystalline silica exists in

several forms (polymorphs) and the most common polymorph is

quartz. The surface of crystalline silica possesses reactive oxygen

species when fractured, which is the reason of crystalline silica

particles toxicity when inhaled (22). A common component of

rock and soils is quartz, and employees may be exposed to dust

that contains quartz during the drilling processs. When drilling

materials contain quartz and are subjected to high temperature, it

may cause the quartz to tranform physically and chemically,

which are eventually exposed to the workers.

c) Particle Size Analyzer

The particle size distribution (PSD) of barite was measured

by using a Malvern Mastersiser 3000 instrument with Hydro EV

Flexible volume wet dispersion (23). The particle size was

determined as volume percentage of particles classed into 101

logarithmically distributed (log-spaced) size bins that ranged

from 0.01 μm to 3000 μm. The signal was transformed into PSD

data by using Fraunhofer or Mie scattering theory with the use of

a laser device software (24). Fraunhofer approximation is a

simplified method. Meanwhile a more accurate data can be

obtained by using the Mie theory, but it requires the optical

properties (refractive index and absorption coefficient of the

sample) and the dispersant. Therefore, the latter provided more

precise results (25). The analysis parameters for both barium

sulphate is shown in the Table 2.

The Agency for Occupational Safety and Health

Administration (OSHA) of Europe and the USA have issued the

guidelines of permissible exposure limit (PEL) for barite to be at

mg/m , 0.05 mg/m for crystalline silica and 0.05 mg/m for oil

mists. The particle size of barite is only controlled by personal

protective equipment (PPE) at the cutoff point of 3.5µm. PPE is

not able to filter a size that is finer than this, which means it will

possibly enter the respiratory system of workers. Taking into

account the occupational risks of drilling fluids, the objective of

this research is to identify the existence of hazardous substances,

such as BTEX in drilling fluids and mists/vapours that are

released into the air, identify the presence of quartz (crystalline

silica) followed by particle size analysis of crystalline silica in

barite.

Results and Discussions

a) BTEX Analysis

Benzene, toluene and xylene were detected at various

locations in the drilling rig with concentrations of 1ppm, 20ppm

and 5ppm, respectively. As there was no benchmark, standards

and acts were available to compare the data collected. Therefore,

this finding clearly showed and shall be considered as a base case

for studying further on the existence of BTEX and its exposure at

drilling rigs. Though the hydrocarbon fractions may contain

insignificant quantities of toxic components, such as BTEX, these

will evaporate at low-boiling point relatively at higher rates,and

thus resulting in higher concentrations of BTEX in the vapour

phase than expected (7). Furthermore, the high level of BTEX

emissions due to ancillary activities associated with drilling

operations were also proven by others (26, 27). Despite the

challenges in setting the standards for health exposure of drilling

fluid to workers, research studies were conducted by the Agency

for Toxic Substances and Disease Registry (ATSDR) for BTEXs

released during agitation of drilling fluids at high pressure and

temperature (7). These results were used as an exposure indicator

or lowest observed adverse effect level (LOAEL) for workers’

exposure to drilling fluids. This indicator may act as a guideline

to help decrease the adverse effects of exposure.

Materials and Methods

Materials

The barite was sampled under controlled conditions from a

barite storehouse. All samplings were done on a random basis.

Barite was basically used without further purification. X-ray

diffraction (XRD) and particle size analyser (PSA) were the

analytical methods used for barite. XRD was used to identify the

presence of crystalline silica, while PSA was used to determine

the particle size. As for the mists/vapours, the sampling and

measuring were conducted during recirculation of drilling fluids.

Oil vapour was dispersed into the atmosphere when the high

temperature drilling fluids were circulated out from the well. As

the drilling floor, shale shaker, chemical mixing station and mud

pits/tanks are identified as the highest possible locations where

workers are subjected to exposure of mists/vapours,all samplings

for BTEX analysis were conducted in these areas. The Gastec

sampling method was used to analyse the BTEX level. The details

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2020, Volume 8, Issue 3, Pages: 1029-1035

b) Identification of Crystalline Silica

supported and matched with the crystalline silica XRD analysis

by others (28,29).

The dominant peak as shown in Figure 2a is the XRD analysis

result for barite. The samples were analysed at 2θ values from 20

to 35. The peak was close to the selected reference data provided

for silicon dioxide, as shown in the Figure 2b. This peak was also

Table 1: Type of gases to be measured

Benzene Detector

Toluene Detector

Xylene Detector

Measurement Range (ppm)

No. Pump Stroke

0.1 to 10

10 to 300

10 to 250

Correction Factor

Sampling Time (minute/stroke)

Detecting Limit (ppm)

Color Change

1.5

0.05

1.5

White to Dark Green

White to Brown

Reaction Principle

->I

6 4 3 2 5 2 4 2

C H (CH )+I O +H SO ->I

Figure 2a: XRD analysis for barium sulphate

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2020, Volume 8, Issue 3, Pages: 1029-1035

Figure 3b: XRD analysis for barium sulphate with reference data

Table 2: Analysis parameters of barium sulphate

the sites. Furthermore, other than the BTEX and crystalline silica,

the handling of barite is necessary to adhere to the guidelines

where its permissible exposure limit (PEL) is at 5mg/m³.

Analysis Parameters

Particle Refractive Index

Particle Absorption Index

Dispersant Refractive Index

Dispersant

Barium Sulphate

1.643

0.010

Table 3: PSD for barite

1.330

Measuring

Concentration

Results

Water

0.207%

2.740

Span

The PSD for barite is shown in Table 3, as the cutoff point of

.5µm filter in breathing apparatus. There were some portions of

Uniformity

Specific Surface Area

Dv (10)

1.064

particle size, which were below 1µm and it will strengthen the

threat of these particles. Therefore, it will flow through the filter

and possibly be inhaled. Further to the particle size and with

confirmation of the crystalline silica presence in barite, the threat

was imminent to the workers’ health .

713.1m²/kg

3.48µm

Dv (50)

17.8µm

Conclusions

Dv (90)

52.2µm

This paper presents the tangible threats to workers

working on drilling operations at drilling rigs, especially activities

allied with preparation and recirculation of drilling fluids. The

presence of BTEX and crystalline silica in these activities is

confirmed by quantitative analysis of samples taken randomly at

Control measures such as engineering control or PPEs

implementation of these activities should also be reviewed and

revised to ensure the mitigation of occupational risks. The

introduction of new control measures, namely Artificial

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2020, Volume 8, Issue 3, Pages: 1029-1035

Intelligence (AI) and Internet of Things (IoT), whichare aligned

with the 4 Industrial Revolution such as automation in drilling

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isolation

iii) Personal Protective Equipment

apparatus

– zero-leak breathing

Acknowledgment

The authors would like to thank UTM Razak School for partly

supporting this research with the assistance of the grant vot

number (R.K130000.7740.4J302). The authors also thank Mr.

Mohammad Saiful Omar from UTM UPMU and Shell for their

support in conducting the necessary analysis.

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petroleum-contaminated groundwater. Environ Sci Pollut Res.

Ethical issue

Authors are aware of, and comply with, best practice in

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(avoidance of guest authorship), dual submission, manipulation

of figures, competing interests and compliance with policies on

research ethics. Authors adhere to publication requirements that

submitted work is original and has not been published elsewhere

in any language.

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

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Authors’ contribution

All authors of this study have a complete contribution for data

collection, data analyses and manuscript writing.

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