Onshore European gas field 2018 CoMicTM dose optimisation study

An onshore European asset was undergoing a change in downhole corrosion inhibitor formulation, substituting a hydrocarbon soluble inhibitor for a more water-soluble alternative. The chemical was injected in batch doses and timed to allow the chemical to disperse within the system before the subsequent injection, the operator wanted to ensure full system dispersion between doses.

CoMic™ was selected as a management tool due to the ability deploy on-site, the quick processing of data and the ability to rapidly change and optimise system properties to ensure constant micelle presence within the system and inform system management.

CoMic™ was employed to measure the micelle content of samples to determine inhibitor levels between injections. The existing dosing regime was tested first. The results showed that the corrosion inhibitor levels dropped significantly (no micelles were detected) before the next injection cycle began. This indicated that during this time, there was an opportunity to better protect the system.

The operator then trialled alternative injection regimes, including altering pump capacity, injection duration and time between injections, in order to identify a regime where micelles were consistently observed throughout the injection cycle.

Testing of the final regime with CoMic™ confirmed that micelles were detected during all time points in the injection cycle. This indicated that the new regime offered good availability of inhibitor to provide optimal corrosion protection.

SUMMARY

CoMic™ provides an indication of inhibitor availability. In this field deployment, changes in the system were rapidly detected, making it the ideal tool for on-site chemical optimisation. CoMic™ was used to establish a baseline for existing dose rates and demonstrated the response to dosage changes. This produced a tailored recommendation based on field conditions giving confidence that the system’s chemical management was optimal.

Onshore US 2016 CoMicTM dose optimisation study

An onshore US midstream pipeline company wanted to review their corrosion management system across a pipeline spanning three states. The client believed there may be opportunities to save cost by reducing chemical spend while ensuring that the pipeline was fully protected.

The client chose LUX Assure’s CoMic™ product to fulfil this need and supplement their existing data set, as CoMic™ can provide information on both the under and overdosing of corrosion inhibitors.

CoMic™ assesses whether or not a field sample is above, below or at the Criticial Micelle Concentration (CMC), the concentration at which micelles begin to form. This concentration has been independently described as optimal, as it represents maximum protection, whilst avoiding an excess of inhibitor.

CoMic™ is unique as it consists of a quick and simple test, which compares the clients’ corrosion inhibitor availability under current pipeline conditions with this functional level of corrosion inhibitor.

The client tested five points along a 500-mile section of pipe and results are shown below. The testing demonstrated that samples were around the CMC at three points, indicating optimal dose was being achieved

(✓). The second sample point, the furthest distance from a chemical injection point, showed no micelles. This signalled that further testing at the site was required as it indicates a potential corrosion risk exists at this

point (✗). The fourth point indicated an excess of micelles, highlighting that this area may be over-dosed and

there is an opportunity for cost-saving through dose reduction (✓+).

SUMMARY

CoMic™ identified an area of potential corrosion risk and an area of over-dosing, providing the client with data to enable them to fully optimise their corrosion inhibitor for the field conditions. Following this, the client looked to build regular CoMic™ testing into their management system to ensure the system remained optimised over the long-term and to respond to system changes.

Onshore US 2016 Sour natural gas production, wetting agent

An onshore US facility producing high levels of corrosive H2S in the crude extraction process, required chemical optimisation. Traditional film-forming corrosion inhibitors were ineffective against the highly corrosive H2S, leading the operator to use a ‘wetting agent’ in order to prevent iron sulphide build up.

Wetting agents have similar characteristics to film-forming corrosion inhibitors, forming micelles when the ‘Critical Micelle Concentration’ has been achieved. The use of CoMic™ to determine micelle presence was required at this production facility to inform optimal chemical management

CoMic™ was performed on samples onsite to determine micelle presence and the wetting agent dose rate was altered according to the results. The analysis showed that when a dose rate of 110 ppm was being applied to the system there was evidence of micelles, providing confidence that the system was well dosed.

The wetting agent dose was reduced to determine if too much product was being applied. As the results show, reducing the dose rate resulted in a loss of micelle signal, indicating there was limited scope to reduce the dosage and still provide optimal protection.

Onsite CoMic™ testing afforded near real-time results to be achieved, giving confidence that the system in question was at an optimal dose rate when 110 ppm of the wetting agent was being applied.

A recommendation was made that this dose rate should be maintained for optimal protection. This information was then fed into a corrosion management review.

Onshore UK 2016 Baseline of corrosion inhibitor dosage

A UK onshore crude oil processing facility required assistance to ensure their facilities were protected from the effects of corrosion.

Currently the facility is using film forming corrosion inhibitors to protect high value critical infrastructure where optimum inhibitor dosage levels are difficult to establish.

While under-dosing can increase the risk of corrosion, over-dosing of inhibitor can cause emulsion build-up and complex separation issues which are time-consuming and expensive to resolve. CoMic™ methodology was used to ensure the corrosion inhibitor in use was being adequately dosed. The CoMic™ method works by detecting the presence of corrosion inhibitor micelles, a key feature which determines optimal dose rate.

It is the only readily available technology for accurately measuring Critical Micelle Concentration (CMC) in the field.

Corrosion inhibitor tests were carried out in the lab prior to deployment of CoMic™.

Using a model brine similar to that of the production facility allowed a picture of the chemical's micelle behaviour to be established. Once at site a number of locations were selected from which suitable water samples could be collected. The results showed that all sites were just above the CMC, indicating that adequate corrosion inhibitor was being dosed throughout the system. In addition, these results were combined with the operators in-house LC-MS method which provided support to the results determined by the CoMic™ method

Through use of the CoMic™ methodology the operator was able to gain assurance of the optimal dose of corrosion inhibitor across the facility.

Valuable results provided by CoMic™ allow for informed decisions to be made as field conditions change, increasing confidence in corrosion inhibitor dose selection.

North Sea, UK 2016 Determination of optimal dose of corrosion inhibitor for protection of high value infrastructure

An offshore UK oil and gas operator employed the CoMic™ methodology as a means of determining optimal dose of corrosion inhibitor across the facility.

The facility comprised of production and processing facilities with oil exported to shore via a pipeline for final re-sale. The corrosion inhibitor in use was primarily oil soluble due to its requirement to protect the oil export pipeline. The oil soluble nature of the product meant that traditional residual techniques for corrosion inhibitor detection were not appropriate. Therefore, the unique methodology employed by CoMic™ was required.

The use of CoMic™ allows optimal dose rate of film-forming corrosion inhibitors to be determined by determining micelle presence in production waters. Film-forming corrosion inhibitors, such as that in use on this facility, form micelles when the ‘Critical Micelle Concentration’, or optimal dose, has been achieved. A field deployment covering five days was carried out to ascertain micelle presence across the asset.

The investigation involved onsite sampling from three sample points across the facility, performing CoMic™ analysis to determine micelle presence and manipulation of the dose rate according to the results.

Initial analysis on Day 1 showed a lack of micelle presence, the operator was informed, and investigation revealed corrosion inhibitor was not being dosed due to a failure in pumping equipment. This was rectified and results showed that the system required an equilibrium time of 10 – 28 hours to achieve adequate corrosion inhibitor coverage, indicated by the positive presence of micelles.

Samples taken from Points 2 and 3, which were co-mingled fluids, showed no micelles and highlighted these areas of the facility may be at risk from underdosing.

Onsite testing allowed the operator to assess corrosion inhibitor dose across the facility. Results were fed into the integrity management system and dose rates were changed accordingly.

North Sea, UK 2015 Diagnosis and optimisation of platform linking pipelines

A cluster of platforms in the North Sea are connected by a network of pipelines.Electrochemical probe and coupon testing produced contradictory indications on the efficacy of corrosion inhibitor dosage on one specific pipeline.

An initial laboratory assessment observed typical film-forming behaviour from the inhibitor, with micelles detected in significant numbers once concentration reached the Critical Micelle Concentration (CMC). In the lab study, this was just below 10 ppm. However, CMC is a function of the specific environment, so the fluid has to be tested in the field if the analysis is to be accurate and useful.

Onsite, analysis of water from each end of the pipeline confirmed that the effective dose entering the pipeline wasn’t present at the exit. This suggested that either an increase in dosage was required, or that an alternative inhibitor should be used.

The operator trialled a replacement inhibitor, with CoMic™ used to analyse two different dosage levels and to help define the optimum concentration of the new chemical. This delivered enhanced protection and assurance against corrosive attack.

North Sea, UK 2016 Analysis and interpretation

A subsea pipeline is shared by several North Sea platforms to transport oil to a processing facility in the UK. Between 1% and 5% of the fluid produced is water, with corrosion controlled by adding film-forming inhibitor. Corrosion rate probes are used to optimise inhibitor content, and a CoMic™ study was commissioned to confirm findings.

An initial laboratory assessment was carried out to ensure that the chemical was a surfactant which can be detected when it forms micelles - other types, such as passivating inhibitors, do not react in this way. This was verified and in the lab study, the Critical Micelle Concentration (CMC) was found to be just below 30 ppm. However, CMC is a function of the specific environment, so the fluid has to be tested in the field if the analysis is to be accurate and useful.

Samples analysed from the water phase of fluid taken from the receiving separator quickly showed the presence of corrosion inhibitor micelles at the terminus, which implied that the entire length of the pipeline contained adequate dosage.

The CoMic™ study confirmed adequate inhibitor dosage but identified variability in micelle levels from different samples. Regular, future monitoring of micelle populations was recommended.

It was also recommended that inhibitor be slug-dosed post pigging as the scraping process is known to temporarily remove inhibitor film.

Downstream processing of fluids involved parallel desalter trains. Our analysis demonstrated differences between trains in the micelle readings after mixing with hot crude. The operator was able to use this information to better understand the distribution and eventual fate of the treatment chemicals.

Alaska, USA 2016 Analysis of inhibitor dosage in large production system

A major production complex at an onshore location in Alaska runs three separate systems dealing with produced water and injected seawater. Concern arose over inhibitor performance, and given the complexity and scale of the systems, integrity loss could have been very costly.

CoMic™ was used to carry out studies on all three systems, with the results of the first exercise described here.

The first system analysed has three interconnected production facilities distributed over a large geographical area, with each facility processing the output of numerous individual wells.

Corrosion inhibitor was injected at each well site, with an extra dose added in one of the lines. The CoMic™ analysis revealed significant differences across the system, with micelle levels above optimal at one facility, below optimal at another, and optimal at a third.

SUMMARY

The CoMic™ analysis highlighted the potential benefits were inhibitor dosage to be altered. A return visit the following year showed optimal corrosion inhibitor levels throughout, which suggests that our work helped avoid potentially expensive loss of integrity.

USA 2016 Analysis of inhibitor dosage in large production system

Certain types of biocides, such as those containing benzyl quaternary amines, have a surfactant component and can form micelles when present in concentrations above the CMC. The study investigated whether biocide micelles could be detected in field samples and used to ‘map’ the biocide across a large US onshore facility.

If so, it would allow the operator to understand the path of the chemical through the system and inform dosing.

Surfactant containing biocides were injected from Unit A on the first and third days of testing; biocide 1 (1000 ppm) on day 1 and biocide 2 (300 ppm) on day 3. An additional injection of biocide 2 was injected to Unit D on day 3.

Biocide 1 was a low surfactant formulation (5%) while biocide 2 was high in surfactant (~60%). Water was taken from the system at varying times during the test period. The following map and graphs show the testing of injection waters from Units A to H through the branch line for biocides 1 and 2.

Readings taken the day prior to batch dosing (Pre) showed no micelle signal indicating untreated water. As samples were taken from the slug front, mid and late the micelle signals are observed to increase as the slug transited the sample point.

Solid lines represent samples connected by timing at the same sample point, while broken lines represent transit between sample points. As can be seen, the micelle signal can be used to trace the passage of surfactant based biocide through a system, even at low concentrations of surfactant.

Unit H was measured around the expected mid-point of the slug but showed low micelle signal. This represents a loss of chemical between Unit G outlet and the sample point of Unit H.

The 'kill dose' of biocide 1 was approximate to the CMC of the chemical, TraxBio™ therefore provided reassurance that a sufficient dose of biocide was present at all sample points along the test line

In a similar fashion, Biocide 2 was traced through Unit G by time on the third day of testing. The results, again, provided confidence that biocide was transiting the system in sufficient dosage. Time monitoring of the samples allows estimation on sample residence times to also be calculated.

• On-site testing afforded near real-time results to be achieved

• Testing showed the path of travel of the biocide through the system and whether it was present at the kill dose throughout the system

• Areas requiring additional dosing were highlighted – alerting the operator to a potential biofouling risk

Effect of production solids on micelle populations

Surfactant-type corrosion inhibitors are designed to adsorb to the internal surface of pipelines, forming a passive hydrocarbon layer to prevent access of corrosive liquid to the pipe surface. When dosed at a high enough concentration, the surfaces in the system will become saturated and inhibitor will accumulate in the production fluids forming aggregates known as corrosion inhibitor micelles. These form at the Critical Micelle Concentration (CMC).

Solids originating from formation residues, corrosion by-products and scale formation can all provide secondary binding sites for corrosion inhibitor, leading to decreased availability and implications for system protection.

CoMic™ and TraxBio™ technology detects micelles in the water phase of oilfield samples to provide information on inhibitor or biocide availability. In this example, micelle detection was used to determine the losses of surfactant to various commonly observed production solids.

The CMCs of four commercially formulated corrosion inhibitors were determined to be below 100 ppm. Separate 100 ppm corrosion inhibitor solutions in 1 M NaCl were prepared and a 20 mL sample of each inhibitor solution was transferred to a vial charged with a known mass of the test solid, sealed and gently agitated at hourly intervals for 5 h. The solutions were allowed to equilibrate for a further 15 h before analysis with CoMic™.

All chemicals showed varying losses of surfactant chemicals to the solids tested. Losses were inhibitor and solids dependent, with inhibitor 1 showing the least reduction in micelle signal with solid mass.

The testing shows that solids in systems can act as a sink for corrosion inhibitor, reducing availability and presenting a possible corrosion risk. Optimal chemical management of a system should consider this impact. CoMic™ can provide a useful laboratory or field tool to assist asset integrity managers and production chemists.

Effect of production solids on micelle populations

Corrosion inhibitors used in the oilfield are generally formulations which consist of multiple chemical components. The surfactant molecules which provide the corrosion protection can contain different carbon chain lengths and / or different head groups (e.g. imidazoline, quaternary amine).

CoMic™ detects micelles when a fluid contains surfactant above the critical micelle concentration (CMC) but what is the impact of the presence of multiple species? Do mixed micelles form where micelles are comprised of different surfactant molecules or do multiple CMCs exist?

The CMC of two quaternary ammonium chemicals were determined using the CoMic™ methodology; these contained carbon chain lengths of 12 and 14 and are referred to as C12 and C14 respectively.

A 180 ppm solution of C12 was prepared and C14 was added in increasing concentrations from 0 to 50 ppm in 5 ppm increments; the fluids were analysed and the CMC calculated. An equation known from the literature was then used to estimate the CMC of the mixture and compared with the experimentally measured CMC.

The measured CMC for C12 was 357 ppm and for C14 it was 39 ppm.

The CMC of the mixture was 200 ppm, comprising of 180 ppm C12 and 20 ppm C14. Only one CMC was observed. The observation of only one CMC agrees with the literature on mixed micelle systems and it is common for the CMC of a mixture to lie between the CMC of the individual components. An equation can be used to estimate the CMC of a mixture.

1

CMC𝑚𝑖𝑥=

𝜒1𝐶𝑀𝐶1

+ 𝜒2

𝐶𝑀𝐶2

𝜒 = mole fraction of surfactant

Holmberg et al., Surfactants and Polymers in Aqueous Solutions, Wiley and Sons, 2002

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Only one CMC was observed when two surfactants were mixed and analysed with CoMic™, this finding supported the literature calculations. The CMC for the mixture was between the CMCs for the individual components.

When multiple surfactant components are present, for example at a comingled point of two production systems, they will converge and create mixed micelles. The levels of inhibitor in each separate system will not be determinable after comingling, but the mixed micelles can be detected by CoMic™ thereby providing information on the corrosion inhibitor availability in systems.

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