Hydrogen Sulphide (H2S) is a colourless gas that smells like rotten eggs (from the sulphur). Often referred to as "sewer gas," hydrogen sulphide is highly poisonous as well as corrosive. Small concentrations in air may be fatal in minutes. Hydrogen sulphide can be found as a component of formation gases, dissolved in water, hydrocarbons, or even liquid sulphur (King, 1974). Thermal degradation of organic materials and sulphate reducing bacteria (SRB) can create hydrogen sulphide along with other gases. Although hydrogen sulphide can have adverse effects on viscosity, fluid loss, and fluid chemistry.

1. CHEMICAL SCAVENGERS FOR SULPHIDES IN DRILLING FLUIDS
– A REVIEW
BY
M.K. AMOSA
I. A. MOHAMMED
S. A. YARO
PRESENTED AT THE
7THCHEMCLASS CONFERENCE 2009
THEME :– GREEN CHEMISTRY: A NEW PATHWAY IN R&D AND
ENVIRONMENTAL CHEMISTRY
HELD ON 11TH JUNE, 2009 AT NARICT, BASAWA, ZARIA.

2. Introduction
Hydrogen Sulphide H2S
Hydrogen Sulphide (H2S) is a colourless gas that smells like rotten eggs (from
the sulphur). Often referred to as "sewer gas," hydrogen sulphide is highly
poisonous as well as corrosive. Small concentrations in air may be fatal in
minutes. Hydrogen sulphide can be found as a component of formation gases,
dissolved in water, hydrocarbons, or even liquid sulphur (King, 1974). Thermal
degradation of organic materials and sulphate reducing bacteria (SRB) can
create hydrogen sulphide along with other gases. Although hydrogen sulphide
can have adverse effects on viscosity, fluid loss, and fluid chemistry
safety is the most important issue
Usually, the poisoning caused by hydrogen sulphide is through inhalation and
has a toxicity similar to cyanide. It is found in petroleum and natural gas and
is sometimes present in ground water. (KMC Oiltools, 2006)

3. Introduction (Contd.)
HYDROGEN SULPHIDE H2S
•Relying solely on its odour is not a good idea because at
concentrations above 100 ppm it deadens a person’s sense of smell
within a few minutes.
•The pure gas is heavier than air and can collect in low areas such as
pit rooms and accommodation (KMC Oiltools, 2006).
•The term “sulphides” used in oil and gas opeartions includes all three
water-soluble species H2S, HS- and S2- (Garret et al, 1979).

4. Introduction (Contd.)
HYDROGEN SULPHIDE H2S

5. CORROSION
Introduction (Contd.)
Dissolved H2S
• Both the hydrogen and sulphide ions increase corrosion.
• Hydrogen can also enter the mud by bacterial action or thermal
degradation of organic additives.
• Under normal conditions the hydrogen gas molecule is too large to
enter the steel and it bubbles off .
• In the presence of the sulphide ion, the hydrogen gradient into steel
is increased, the hydrogen tends to attack sites that are highly
stressed (and thus more likely to fail).
• The hydrogen causes small cracks that lead to sudden brittle
failure, called hydrogen embrittlement, or hydrogen stress cracking
(Cater et al, 1985).

6. Introduction (Contd.)
Dissolved H2S
• Hydrogen generation
depends on the pH of the
environment . Low pH values
increase hydrogen
availability.
• At pH values of less than 6,
string failure due to H2S can
occur in less than 1 hour. At
pH's above 8, the time to
failure increases to beyond
100 hours. (KMC Oiltools,
2006)
11
9
7
5
3
100 1 10
Time to Failure (hrs.)
pH

7. Introduction (Contd.)
Dissociation of H2S with pH
•Raising the pH is a
good quick reaction
to H2S …
•However sulphide
scavengers must be
used as soon as
possible because if
the pH drops the H2S
will form again and
come out of solution
(Garret et al, 1979)

8. Hydrogen Sulphide Scavenger Technology
An Ideal Scavenger has to meet the following
requirements (Garrett et al, 1979):
 Complete, fast, and irreversible reaction with H2S under
all mud conditions;
 Should be able to undergo a quantitative reaction with
sulphide;
 pH stability of up to and beyond 11.5;
 Non-corrosive to metals;
 Easy and safe to handle and non-polluting to the
environment;
 Non detrimental to mud’s rheology;
 Must have a good environmental acceptability before
and after reaction with sulphide.

9. Environmental Concern
Due to the high environmental awareness, there are laws
regulating the use and discharge of chemicals after
operations. Only the chemicals that fall within the
GREEN/PLONOR (Posses Little Or No Risk) list could be
discharged.
 The offshore Oil and Gas Industry Strategy of OSPAR
(Oslo and Paris conventions regulating offshore
discharges) sets the objective of “… preventing and
eliminating pollution and taking the necessary measures
to protect the maritime area against the adverse effects
of offshore activities so as to safeguard human health
and of conserving marine ecosystems” OSPAR Commission.
(OSPAR Commission, 1995)
 “Development of new technology is important in
reducing discharges of environmentally hazardous
substances” Ministry of Petroleum and Energy 2005 Environmental Report.
(OSPAR Commission, 1995)

10. S Scavengers A Brief Overview of the H2 used in Drilling Fluids
Many well-known mechanisms have been employed for the
immobilization of H2S from drilling fluid viz:
 Copper carbonates (Carney and Jones, 1974)
 Hydrogen peroxide (Carney and Jones, 1974)
 Zinc compounds; especially basic zinc carbonate (Garrett et al,
1979)
 Iron oxide; especially magnetite (Garrett et al, 1979)
 Chlorine containing compounds (e.g. chlorine dioxide and
sodium hypochlorite); (Charles et al,1985)
 Organic compounds (e.g. acrolein and formaldehyde),
methanol, glyoxal, amines, triazines, naphthenates, chelates of
ethylenediaminetetraacetic acid – EDTA,
hydroxyethylethylenediaminetriacetic acid – HEDTA,
nitrilotriacetic acid – NTA among others), etc.

11.  The most HSE compliant scavenger in drilling fluids so
far is magnetite. This scavenger has a limitation of low
reaction rates in high pH but faster rates in low pH muds
(Garrett et al, 1979, KMC Oiltools, 2006).
 Whereas muds’ pH are not usually allowed to go below
9.5. It is usually between 10 and 11.5 (M-I, LLC, 2001).
 Although commercial Zinc-containing compounds (ZCCs)
are very effective but pose rheological and
environmental problems (Ray et al, 1979).
 Zinc metal has been classified as a toxic substance,
concentrations as low as 0.15 ppm contamination could
be potentially hazardous, hence, rendering the ZCCs as
environmentally non-viable (Martin, 2005).

12.  Efficiencies of some organic compounds like Acrolein,
Formaldehyde, and chelates like EDTA, NTA etc as
sulphide scavengers have been reported. Their
reactions with H2S are too complex to be predicted,
and besides, there are outstanding questions
concerning HSE, especially the health aspects of
reactants and reaction products of the organic
compounds/chelates. Formaldehyde has been
clearly confirmed to be carcinogen (Nasr-El-Din et
al, 2002).
 These organic compounds and chelates usually
renders themselves easily for sweetening purposes
rather than application in muds (Sitz et al, 2003).

13.  Complexes of iron in the Fe2+ oxidation state are usually less
sensitive to pH values (Shriver et al, 1999).
 Fe2+, ferrous ion is a necessary trace element used by all
known living organisms. It is also used in fertilizing aquatic
plants (Anonymous, 2007).
 Gluconic acid is generally recognised as safe (GRAS). Also,
sodium, calcium and iron salts of gluconic acid have been
confirmed mild, non-volatile, non-corrosive and non-toxic.
They are stable up to alkaline pH values and are also stable
at high temperatures. A metal gluconate is comparatively
better than EDTA, NTA and other chelators (Ramachandran
et al, 2006).
 Most metal gluconates are confirmed HSE compliant
materials especially the iron, sodium, zinc and calcium salts
of gluconic acids which are used for medicinal purposes in
both humans and animals (Ramachandran et al, 2006).
 The inhibitive effect of calcium gluconate on carbon steel in
neutral aqueous media has been put to test due to its non-toxic
and eco-friendly nature and found satisfactory (Shibli
and Kumary, 2004).

14.  Eric (2004) disclosed that ferrous gluconate could have an efficient
sulphide removal from drilling fluids.
 Amosa (2009) did more works on the use of ferrous gluconate as a
scavenger by simulating the real well-bore operating conditions in
the laboratory tests performed.
 According to the OSPAR Convention GREEN/PLONOR classifications,
this compound is found to be environmental benign and falls in
GREEN category due to the fact that Log Pow (OECD 117) is zero
which indicates very little potential for bioaccumulation, aerobic
ready biodegradability in sea water using OECD 306 is very good
(greater than 70 %) and it has a low toxicity as confirmed by the
OSPAR protocol (OSPAR Commission, 1995).
Probable reaction with sulphides:
Fe (C6H12O7)2 + S2- → FeS + 2 [C6H12O7]-
Ferrous gluconate + Sulphide →Ferrous sulphide + gluconate

15. Conclusions and Recommendations
 Hydrogen sulphide scavengers are employed in more than one field applications like
drilling operations and sweetening processes; and the type of scavenger needed for
a particular application depends whether it can act better in that medium.
 Although there have been many findings on sulphide scavengers, each one of them
has one or more limitations, ranging from attributed exorbitant prices to Health,
Safety and Environmental (HSE) problems.
 Ferrous gluconate has been recently found to be efficient and environmentally
benign but the laboratory tests still need be translated into real rig-site operation. It
should also be tested in other media other than drilling fluid so as to evaluate its
hydrogen sulphide scavenging ability in these media.
 Optimization studies on the reaction between ferrous gluconate and hydrogen
sulphide need be done.
 There exist more research needs to develop or source for hydrogen sulphide
scavengers, perhaps embodying complementary mixtures of chemicals or a
compound specifically investigated to fit the needs and match more closely the
qualities of an ideal scavenger.
 Thorough testing is necessary for any particular sulphide scavenger sourced or
designed so as to know if it has satisfactory scavenging ability in every applications;
and if it will not adversely affect the rheology (when used in drilling mud) at various
conditions of temperatures and pressures. Otherwise, the researcher on the
particular scavenger should state the medium where the scavenger is mostly fit for
application.

16. THANK YOU
FOR
LISTENING