A collaborative project case study evaluation for a confidential client with assets in Australasia: mercury chemical decontamination (total mass removal in preparation for decommissioning vs near total mercury mass removal from high value equipment. ISCT manufactured and provided the chemistry, experience and technical know-how to jam out these state of the art chemical decontamination projects using the latest performance based measurement technologies. ISCT also provided environmentally safe spent fluids processing chemistries and technology.

1. Reprinted from August 2016
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M
any in the oil and gas industry are now aware of the effects of
produced mercury on hydrocarbon processing systems, and
that produced mercury contaminates processing equipment
and transportation systems from the riser platform to onshore
dehydration plants, and throughout the front end of natural gas liquids
(NGL) and LNG plants. Downstream processing (refining and petrochemical)
plants are also affected, and have process, environment, health and safety
(EHS), and occupational exposure risks. Certain production regions around
the globe are facing the same challenges at the same time, where assets are
operating past their economic design, and are also contaminated with
mercury (topside process equipment on production platforms, gathering
platforms, floating production storage and offloading units [FPSOs], subsea
pipelines and hydrocarbon processing plants). The continued operation,
dismantling, removal and disposal of these systems present unique
challenges and risks to personnel, the environment and marine/terrestrial
ecosystems.
Global conventions provide guidance for decommissioning of oil and
gas facilities in international waters, but specific regulations with regard to
residual mercury concentrations in production systems (either as scale or
complexed in the grain-boundary of metals) are not currently available.
Decommissioning regulatory guidance updates are anticipated in Asia, but
may not provide a specific mercury mass per surface area or concentration
that can remain in process systems. Mercury is a trace metal in all
A
DEEP
CLEAN
Ron Radford and Tim Jenkins P.E., PEI Mercury & Chemical Services Group, USA,
discuss the mercury chemical decontamination of hydrocarbon processing systems.

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hydrocarbons, but is concentrated in specific oil and gas
basins and during production, therefore international and
regional decommissioning guidelines should be drafted
and/or amended to address residual mercury mass and
distribution within assets scheduled for decommissioning.
Notably, decommissioning assets on the northwest shelf and
onshore Western Australia (Figure 1) follow an
objective-based approach under a legislative framework
regulated by the Department of Mines and Petroleum (DMP)
that ensures decommissioning is managed responsibly and
sustainably for the benefit of all stakeholders (e.g., DMP is
required to consider mass and distribution of THg
contaminating each system during pre-decommissioning
planning).
Mercury is a naturally occurring trace constituent of coal,
crude oil, natural gas, and natural gas condensate. Virtually all
geologic hydrocarbons contain measureable quantities of
mercury. Coal bed methane (CBM) production can contain
higher mercury concentrations than traditional or shale gas
production. Trace metals, including mercury, are scavenged by
carbon/stainless steel (adsorbed/chemisorbed) into interfacial
surfaces and can complex into the scale/metal grain
boundary, requiring special chemistry and chemical
application methods for successful decontamination. The
accurate measurement and quantification of mercury in
operating and non-operating process systems is challenging,
and, even though this science and technology has advanced to
its most accurate level in the last decade, many operators have
not quantified mercury mass loading per surface area or flux
throughout production systems scheduled for
decommissioning. Understanding mercury mass per surface
area, speciation, depth profile, and distribution within a
system, is a critical first step to developing accurate
decommissioning, chemical decontamination and spent
chemistry processing plans. The development of these plans is
imperative, and required to develop accurate cost estimates
for each phase. The more assumptions that are made in this
process, the less accurate the cost estimate to manage each
phase will be. Costs are a critical factor in decommissioning
programmes and, in this new energy market supply and
demand paradigm, it is more important than ever for
operators to understand what those costs will be.
Research and development
PEI and its research partner International Specialty Chemicals
and Technology (ISCT), based in Sydney, completed two
important mercury mass loading, chemical reduction and
materials processing research programmes in 2014/2015 that
advanced PEI's chemical and processing technologies to state
of the art. Three major objectives were achieved in these
research programmes:
n Enhanced chemical formulations with modified surface
reactive agents effective in cold water environments
(i.e. subsea pipeline applications) tested 100% effective in
temperatures as low as 10˚C.
n Increased chemical contact time on simulated vertical
surfaces (i.e. FPSO cargo holds using existing infrastructure
for chemical application) tested 97% and 99.7% effective
in sequential applications.
n Processed simulated spent chemistries (chemistries spiked
to 9000 ppm mercury and 1000 ppm hydrocarbons)
treated to <1 ppb residual dissolved mercury in solution.
These achievements were combined to develop a
P80 cost estimate for full scale implementation.
What this means for the hydrocarbon processing industry
is that the technology required for 'near total' and 'total'
mercury mass removal from process systems has finally caught
up to the need for such technology. Furthermore, the disposal
and treatment challenges posed by spent chemistries can now
be effectively managed though 'discharge ready' processing,
eliminating an expensive waste stream that previously had few
options for disposal.
Full scale application
A summary of two mercury chemical decontamination
projects performed for confidential producers with operations
in Australasia is provided below: mercury chemical
decontamination of process equipment scheduled for
decommissioning, and mercury chemical decontamination of
high value equipment for re-use. In each case, near total and
total mercury mass removal was an objective, and spent
chemistry processing goals were to be treated to discharge
criteria.
In the first case, a section of 14 in. inlet piping was
removed from a liquified petroleum gas (LPG) mercury
removal unit (MRU) offshore, as part of ongoing maintenance
Figure 1. Australasian production.
Figure 2. Post-decontamination XRF data.

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and inspection. The section of piping was scheduled for
chemical decontamination in preparation for
decommissioning (metals recycling). A critical step in any
chemical cleaning programme is to determine the
decontamination objectives and establish the performance
criteria of the programme. The piping section was designated
for metals recycling; therefore, to meet decommissioning
criteria for safe recycling, approximately 99% mercury mass
removal was required and accomplished using a sequential
chemical cleaning approach. Initial mercury mass loading per
surface area ranged from 10 - 60 g/m2. Chemical
performance and maximum mercury uptake for the
chemistries selected have been well established in ongoing
research and development since 2014 (ISCT 400-66 and
ISCT 400-69). However, during chemical circulation, a range
of performance analyses were performed continuously to
measure the performance of the chemistry (THg, PHg, DHg,
Fe, pH, % oxidiser[s], NTU and TSS), as well as mercury mass
removed over time. THg and compound uptake graphs were
then generated for each chemical phase, depicting mercury
uptake and trending over time. These graphs provided
valuable information in real time to indicate when to stop a
particular chemical phase, increase an oxidant or reduction
agent, or increase the solubility of mercury in the chemical
solution.
By calculating the difference between initial and final
mercury mass loading measurements, the resulting residual
mercury readings represented more than 99% mercury mass
removal. This was a relatively small section of 14 in. piping,
and was provided to Contract Resources (CR)/PEI to
demonstrate the technology and chemical efficacies for
subsequent use during total asset decommissioning. Total
soluble mercury removed during the three phase sequential
chemical circulation was 23.5 g (21 g of which was removed
in four hours during the first application of 400-66). The
remaining 2.5 g of mercury was removed using two
sequential applications of 400-69 and 400-66 over an
additional eight hours of contact time. Final verification
X-ray fluorescence (XRF) surface measurements are
depicted in Figure 2.
In the second case study (decontamination of high
value equipment for re-use), well flow test equipment and
process systems on a semi-submersible drill ship were
contaminated with mercury due to intermittent exposure
to high mercury concentration hydrocarbon streams during
a 2014 well flow test programme. The semi-submersible and
associated well flow test equipment were scheduled for
re-mobilisation to another production field with lower
mercury concentrations in gas and condensate. Mercury
chemical decontamination was required primarily to
prevent mercury from desorbing from interior steel process
system surfaces during well flow test operations and
affecting mercury sampling and analysis data from the new
production field. The project required performing a study
to determine mercury mass loading, distribution and
speciation of various systems prior to chemical
decontamination offshore on the semi-submersible drill
ship and onshore on well flow test process equipment.
Based on this study, chemical decontamination plans,
performance monitoring criteria and spent
chemistry/materials processing plans were developed. A
key objective was near total mercury mass removal with an
emphasis on avoiding damage to primary 4130 and 4140
steel alloy components.
Most that have performed similar studies know that
mass loading per surface area is generally not homogenous
within systems, and varies with exposure, pressure, the
temperature of the process, the chemical composition of
the hydrocarbon streams, and many other factors. What
was needed was versatility in the chemical’s maximum
loading potential for mercury and hydrocarbons.
ISCT 400-66 was selected, and the formula modified based
on the estimated mercury mass per surface area of the
various systems required for decontamination. Chemical
performance and maximum mercury uptake for
ISCT 400-66 is well established, and solubility of mercury
can be increased to >100 000 ppm. Offshore, on the
semi-submersible, this meant the chemistry had a certain
mass loading potential, and was circulated in four piping
runs of four hours each. The total calculated mass per
surface area for offshore piping on the semi-submersible
was approximately 4 g/m2
, with a total mercury mass
removal of 418 g.
Well flow test systems were re-connected onshore at a
Contract Resources facility for chemical decontamination,
performance monitoring and final verification. Systems
were connected based on estimated mercury mass loading
per surface area in four continuous circulation systems and
circulated for four hours each. A combined total of 1.016 kg
of mercury was removed based on performance and
Figure 3. Pre and post-XRF surface concentrations.
Figure 4. LNG carrier ship.

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verification sampling/analysis of THg. A range of chemical
analyses were performed continuously to measure the
performance of the chemistry (THg, PHg, DHg, Fe, pH,
% oxidiser[s], NTU and TSS), as well as mercury mass
removed over time. THg and chemical compound uptake
graphs were generated for each chemical phase, depicting
mercury uptake and trending over time.
In both cases, XRF baseline and post verification surface
screening was performed using a five point calibrated XRF
in surface mode. PEI has been using XRF technology since
the beginning of the 2014 research programmes to evaluate
the effectiveness and limitations with the overall objective
of deploying the technology as a semi-quantitative method
to determine mercury mass loading per surface area. The
limitations and accuracy need to be understood before
attempting to use XRF technology in a chemical
decontamination verification programme. Also, to further
evaluate the effectiveness of the chemical efficacies and
total mercury mass removal, sacrificial steel (2 - 6 in. high
pressure flanges) from the most mercury contaminated
equipment (three phase separator approximately 80 g/m2)
was sent to a US lab for scanning electron microscopy
(SEM), energy dispersive X-ray spectroscopy (EDS) and acid
digestions to show the overall correlation between XRF
pre and post-screening versus acid digestions of
representative test coupons. PEI has demonstrated, through
its recent research and full scale project applications, a
strong correlation between XRF readings and off-site acid
digestion results, especially for post-verification samples.
Total calculated mercury removal from the combined
systems using the highest mercury mass loading per surface
area equipment as a surrogate for the entire systems
equated to approximately 90 - 95% mass reduction. Figure 3
depicts pre and post-XRF surface mercury concentrations,
and the overlying grid that was used to cut representative
test coupons for SEM, EDS and acid digestions.
Processing spent chemistry and
materials minimisation
In both cases, spent chemistries were processed onsite
using a combination of methods based on bench testing
each batch (approximately 10 500 l per ISO to allow for
volume expansion, sulfide deactivation and modified
Fentons Reagent). There are few disposal options for high
concentration mercury contaminated fluids (>5000 ppm) in
many offshore/onshore environments. The best case is
having an injection well available where limited processing
is required (pH adjustment and %TSS). Processing can be as
costly as the chemical decontamination, depending on
what the discharge criteria are and what the final disposal
options are for the supernatant and sediments generated
from flocculants/coagulants. In general, the processing
steps for both cases consisted of pH adjustment in the
presence of H2
S inhibitors (if not performed properly, this
reaction can release hazardous concentrations of H2S). An
intercooler/heat exchanger is required to control reaction
temperatures, as well as direct chemical performance
monitoring equipment, including an explosion-proof
camera, to observe reactions in each batch. Processing
analysis is required for a variety of parameters, similar to
those used to measure the performance of the chemical
decontamination. After pH adjustment and sulfide/H2
S
deactivation, subsequent processing phases included
flocculation, coagulation and settlement/decantation.
Supernatant was transferred to a set of clean ISOs for final
treatment and offsite disposal. A variety of chemical
solutions were processed in batches, including chemistries
used to clean process tanks, pumps and equipment that
were exposed to the chemical decontamination and/or
minimisation process (variable pH range and
mercury/hydrocarbon concentrations). The final stage of
materials processing consisted of dewatering the
sediments, which, in both cases, was accomplished using a
centrifuge to minimise the sludge volume. This resulted in a
relatively small volume of highly concentrated mercury
containing filter cake, and could be disposed under either
the Basel Convention at a permitted facility, or sequestered
for long term storage.
Conclusion
Both of these cases can be considered ‘proof of concept’
successes, and can be used as a model for similar projects,
both offshore and onshore. An important lesson learned is
that accurate mercury assessment, distribution, depth
profile analysis and speciation are key to developing
accurate chemical decontamination/processing plans,
costs and schedules. As mentioned before, assumptions
can lead to less accurate cost estimates and greater adverse
effects to project schedules. The impacts of PEI's latest
mass loading and chemical reduction research and full
scale chemical decontamination/materials processing
applications are a promising and positive development to
the decommissioning industry. Applying these technologies
and methods will reduce the costs of decommissioning by
eliminating variables that, if not included in pre-planning,
would negatively affect the schedule, compliance and,
thus, costs.
PEI has developed a unique approach to understanding
mercury mass flux, loading and distribution in hydrocarbon
processing systems to develop mercury management
processes, including chemical solutions for
decontamination and materials processing. The focus is to
share that technology and approach with the company's
alliance partners (CR) and the hydrocarbon processing
industry in the Australasian region. The regional alliance
with CR builds on an existing alliance with CR Asia and
extends PEI’s research and development, process stream
sampling and analysis, and mercury chemical
decontamination services throughout Australia,
Papua New Guinea and New Zealand. Through the alliance
with CR and the company's research partner ISCT, PEI is
committed to improving and developing chemical
technologies to support mercury management and
chemical decontamination projects for operating assets,
and those scheduled for decommissioning.
Notes
This paper was first presented at the Decommissioning
and Mature Wells Management Conference on
2 - 4 December 2015 in Kuala Lumpur, Malaysia.