bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extreme Challenges in FeS Scale Cleanout Operation Overcome using Temporary Isolation, High Pressure Coiled Tubing, and Tailored Fluid Systems
Authors: Buali Mustafa , Ginest Noel , Leal Jairo , Sambo Oscar , Chacon Alejandro , Vielma Jose 
Published: February 2021

Abstract
The carbonate gas producing zones of the Ghawar field have been impacted by extensive FeS scale deposition, reducing overall gas production and significantly increasing risks of well interventions. Previous remediation included the use of workover rigs, which can be costly because of the time necessary for workovers and lost production. H2S levels (2 to 5%) found in the reservoir also contribute to higher costs and risks when using workover rigs.
A chemical solution was also considered, but the FeS could not be 100% dissolved with HCl and the chemical reaction generated large amounts of H2S in addition to existing high levels of H2S in the reservoir. This poses a safety concern with the returns at surface along with potential corrosion of the coiled tubing (CT) and completion. Therefore, the safest and most economical method was deemed to be mechanical descaling with CT.
This paper discusses two wells where mechanical descaling was applied using CT. Each well involved four major challenges that included low reservoir pressure, increased reservoir temperature, horizontal openhole completion, and scale with high specific gravity (3.7 to 4.3). The low reservoir pressure required pay zone isolation to allow for returns to circulate out the heavy scale and to minimize fluid losses to the formation. The fact that the wells had long, openhole sections created another challenge for isolation and cleanout. With a bottomhole temperature (BHT) as high as to 310°F, the operational envelope of temporary chemical packers in combination with loss circulation materials (LCMs) to isolate the openhole section had to be expanded. Following mechanical descaling with CT, the final challenge discussed in this paper is the process to clean out the LCM in the horizontal openhole and bring the well back to maximum gas production using pinpoint stimulation techniques.
Correlation of Shear and Turbulence on Scale Formation and Inhibition
Authors: Graham Gordon M. , Thomson Hunter , Bowering Deborah , Stalker Robert 
Published: February 2021

Abstract
Current scale risk analysis focuses on thermodynamic calculations to determine the risk of scale, ignoring system kinetics and the impact of flow regimes on scale precipitation from mildly oversaturated systems. It is however recognised that flow regimes affect scale precipitation. Surface growth is influenced by mass transport and diffusion which are susceptible to shear stress and turbulence. Little work has been reported which examine these factors under conditions that can be readily tuned to match field production conditions. Scale inhibitor evaluation exercises therefore often rely on conventional low shear/static or laminar flow conditions which have been demonstrated in many papers to be largely inadequate for mildly oversaturated systems.
This work addresses this concept and focuses on scale deposition and growth at metal surfaces as well as bulk (liquid phase) nucleation and growth in mildly oversaturated brines as a function of increasing shear. A series of controlled experiments have been conducted under “mildly oversaturated” conditions to examine the effect of; no shear conventional “static” tests, moderate shear mixed statics and much higher shear regimes including rotating cage and jet impingement approaches with calculated shear stresses up to 500 Pa and higher. This builds on previous work published by the authors in this area1 and further illustrates the importance of conducting tests at field representative shear conditions. Since shear and turbulence have a governing effect on the critical scaling tendency (the level of oversaturation below which brines remain stable under normal production conditions) the ability to correlate between shear and the propensity for scaling in mildly oversaturated systems is critically important in determining the risk of scale at different locations in the production stream.
New test methods have been validated which allow the impact of shear and turbulence to be observed under conditions more representative of production conditions. These methodologies lead to scaling in mildly oversaturated brine systems without having to adjust brine chemistry or otherwise increase the scaling regime, i.e. by adjusting the flow regime to reproduce the shear expected at critical locations in the production system. Improved methodologies are therefore presented which allow more appropriate scale inhibitor qualification, taking into account the impact of shear and turbulence under field representative conditions. The work shows that this is critically important for mildly oversaturated conditions.
An Assay Method for the Detection of all Scale Inhibitors at Extremely low Concentration
Authors: Liu Ya , Kan Amy T. , Yan Chao , Wang Fei , Wang Lu , Tomson Mason B. 
Published: February 2021

Abstract
Accurate detection of scale inhibitors has always been vitally important to monitor scale treatment during oil and gas production. However, there remains an ongoing challenge to analyze scale inhibitors at low concentrations, especially with polymeric scale inhibitors. This paper presents an assay method designed to detect all types of scale inhibitors, especially at low concentrations, and an expert program developed to guide the method. The program guides the preparation of a field brine barite solution at a fixed barite super-saturation. Scale inhibitor concentration is then measured via the method of standard additions, assuming a linear relationship between the scale inhibitor concentration and the logarithm of barite induction time. Seven different scale inhibitors, including phosphonates, carboxylates and sulfonates, were detected in two typical synthetic brines at low concentrations. In addition, this assay method has also been applied to scale inhibitor detection in actual field brines. In general, this easily-implemented method can directly detect the residual level of any scale inhibitors in field brine within the range of about 0.3 – 100 mg/L active. Emphasis in this paper is on low concentrations. Measurement of low concentration scale inhibitors not only help to monitor scaling tendency but also effectively prevent overuse of scale inhibitors and thereby protects the environment and saves money. This is the first method that can detect all scale inhibitors at extremely low concentration. Field applications, strengths, and interferences will be discussed using laboratory and field examples.
Concept, Design and Implementation of a Halite Scale Mitigation Completion in a Gas Well
Authors: Maxwell Doug , Young Keith 
Published: February 2021

Abstract
A North Sea operator was planning to sidetrack an existing gas well to access untapped reserves with an extended reach, sub-horizontal reservoir target. The well was expected to deposit halite scale in the lower part of the completion and across the sandface based on experience from other wells in the field and a production chemistry desk study, possibly from initial production. The project team investigated completion concepts for the well that would address the scaling issue and selected the most appropriate concept prior to designing and planning a practical installation. Several concepts were examined for practical application, including a detailed risk review, before a capillary water delivery system was selected. This involved running 3 capillary lines through the production packer to chemical injection valves deployed on a pre-perforated tailpipe inside the lower completion. As this lower completion was a 5” perforated liner, significant tolerance challenges had to be overcome. The well was completed with the selected concept in January 2013, with the water delivery system injecting 8 bbls of water per day from initial production. The well is on stream and producing at higher than expected rates, with no halite scaling issues identified. By identifying potential flow assurance issues at the concept stage, innovative applications of existing technology can be considered and applied. A multidisciplinary project team is required to meet the demands of such a challenging project. With halite scaling becoming increasingly problematic in the North Sea, the application of water delivery completion concepts may become key to future developments.
Predicted and Observed Evolution of Produced Brine Compositions, and Implications for Scale Management
Authors: Hu Yisheng , Mackay Eric , Ishkov Oleg , Strachan Alistair 
Published: February 2021

Abstract
Produced water was sampled and measured repeatedly during production from an offshore field, and an extensive brine chemistry dataset was developed. Systematic analysis of this dataset enables an in-depth study of brine/brine and brine/rock interactions occurring in the reservoir, with the objective of improving the prediction and management of scale formation, prevention and remediation.
A study of the individual ion trends in the produced brine, using the types of plot developed for the Reacting Ions Toolkit (Ishkov et al., 2009), provides insights into what components are involved in in situ geochemical reactions as the brines are displaced through the reservoir, and how the precipitation and dissolution of minerals and the ion exchange reactions occurring within the reservoir can be identified. This information is then used to better evaluate the scale risk at the production wells.
A thermodynamic prediction model is used to calculate the risk of scale precipitation in a series of individual produced water samples, thus providing an evaluation of the actual scaling risk in these samples, rather than the usual theoretical estimate based on endpoint formation and injection brine compositions, and the erroneous assumption that no reactions in the reservoir impact the produced water composition. Nonetheless, the usual effects of temperature, pressure and brine composition are accounted for in these calculations using classical thermodynamics. The comparison of theoretical and actual results indicates that geochemical reactions taking place in this given reservoir lead to ion depletion that greatly reduces the severity and potential for scale formation. However, ion exchange reactions are also observed, and these too affect the scale risk, and the effectiveness of scale inhibitors in preventing deposition.
Additionally, comprehensive analysis using a geochemical model is used to predict the evolution of the produced brine compositions at the production wells, and to test the assumptions about which in situ reactions are occurring. A good match between the predictions from this geochemical model and the observed produced brine compositions is obtained, suggesting that the key reactions included in the geochemical model are representative of actual field behaviour. This helps to establish confidence that the model can be used as a predictive tool.
Sulfide Scale Control in Produced Water Handling and Injection Systems: Best Practices and Global Experience Overview
Authors: Wylde Jonathan J. 
Published: February 2021

Abstract
Iron sulfide scale is found almost ubiquitously in maturing oilfield produced water handling and injection systems. Keeping injection systems clean of sulfide scale is becoming more of a shared challenge, but there are few examples where true root cause analysis has led to specific laboratory testing and development of bespoke removal and prevention methods. This paper aims to link these aspects by sharing the best practices from around the world with cutting edge techniques and chemistries used to maintain flow assurance and injectivity in produced water handling systems affected by iron sulfide scale.
Discussion includes root causes analysis of iron sulfide scale formation and deposition mechanisms focusing on the interplay of pH, along with sources of iron and sulfide. The paper goes onto discuss laboratory and field evaluation of control methods. Finally, the root causes of iron sulfide scale formation and deposition mechanism, including the relative advantages and merits of the different techniques, including:
Chelating agents (for iron sequestration) Surfactants (for water wetting) Biocide (to target SRB and biofilm) Corrosion inhibitor (to lower iron in system) Sulfide scale inhibitors (threshold inhibition of scale)
Additionally, case histories are used to elaborate the theoretical discussion. The first case history is from an offshore oilfield water injection system, where fouling occurred due to changes in the flow assurance strategy further upstream and capture the lessons learned on the interplay of different production chemicals. The second case history concerns an onshore oilfield with a vast water injection system of over 3,000 wells supporting approximately 5,000 production wells.
The paper concludes with a summary of the decades of experience of solving the most challenging sulfide scaling scenarios, as well as cutting-edge research on a new class of polymeric exotic sulfide scale inhibitor dispersant, effective as threshold concentrations against even lead and zinc sulfide.
Sulfide Scale Control: A High Efficacy Breakthrough Using an Innovative Class of Polymeric Inhibitors
Authors: Savin A.J. , Adamson B. , Wylde J.J. , Kerr J.R. , Kayser C.W. , Trallenkamp T. , Fischer D. , Okocha C. 
Published: February 2021

Abstract
Prevention of sulfide scale through the use of chemistry is a developing area of focus within the oil industry. There are few examples of a single chemical approach working, where scale inhibitor species function at threshold concentrations. Partial inhibition may be provided by ‘standard’ scale inhibitors using established chemistries such as phosphonates or polymeric species. However, the efficacy of these inhibitors against sulfide scale is generally poor and high concentrations are typically required.
Based on an industry need for a true, high-performance sulfide scale inhibitor, work was undertaken to develop a novel chemistry that would offer a step-change in performance from existing technologies. Using a new advanced rapid screening technique, a wide range of ‘standard’ scale inhibitors were assessed, which proved that the majority of these chemistries display no efficacy against sulfide scale. A select few of the standard scale inhibitors displayed limited efficacy and from this data common molecular features which contributed to sulfide scale inhibition were identified.
Utilizing this knowledge, a range of novel polymeric chemistries were synthesized which provide significantly superior inhibition than any other postulated for this application. It has been possible to identify specific moieties within these complex polymers which are required for sulfide scale inhibition and to theorize on likely molecular structure-performance relationships for this new class of scale inhibitor. Additionally, hypotheses on the specific mechanisms by which these inhibitors function have been provided, showing why they are so successful at sulfide crystal growth retardation.
Static and dynamic test methods are described that accurately mimic formation of these scales in the field, in comparing the novel polymeric chemistry with the best-performing ‘standard’ scale inhibitors. Order of magnitude increases in performance over standard species are reported which represents a true step-change in the efficacy of sulfide scale inhibition.
The Challenges Associated with Reaction Products Left in Scale Inhibitor Species after Radical Polymerization
Authors: Wylde Jonathan J. 
Published: February 2021

Abstract
The use of polymeric scale inhibitors has been ubiquitously accepted by the oil and gas industry for many years. There are many benefits to the use of this type of chemistry that include aspects such as high performance, scale species selectivity, enhanced brine compatibility, favorable environmental properties and high thermal stability.
A very common way to manufacture polymeric scale inhibitors is via free radical polymerization. Here an initiator is used to propagate the generation of free radicals from a species, such as hydrogen peroxide. The initiator chemistry can be very varied and usually comprises different types of transition metal salts, hypophosphite or persulfate species. Different monomer units can be polymerized using different initiator and free radical species to yield the same polymer. However, subtle differences can result, including poly-dispersity, average molecular weight and different residual composition. The implications for the end user of the chemistry can be profound regarding performance differences in aspects such as detectability, compatibility, thermal stability and sometimes even scale inhibition and adsorption efficacy.
A case study has been presented where a very commonly used sulfonated copolymer species from four different sources was evaluated in a whole host of compatibility and performance tests. The different routes used different combinations of hydrogen peroxide and transition metal initiator or persulfate/hypophosphite combinations as the free radical source.
There were major differences seen in the compatibility of these products with different scale inhibitors and then in performance. The tests performed highlighted the differences that can occur between the different radical polymerization synthetic routes mentioned above.
The conclusions show that there are many benefits to being able to control the manufacturing process of scale inhibitor species in order to ensure the full composition is understood and can be quantified. The benefits to owning the supply chain are highlighted and lead to not only better control of quality and cost but, more importantly, to the overall risk reduction for the end user in the end use application.
Coupled Adsorption/Precipitation Tests with a Phosphonate Inhibitor and Carbonate Substrate
Authors: Thomas W.S. , Sorbie K.S. , Singleton M.A. 
Published: February 2021

Abstract
A series of static adsorption/precipitation tests has been carried out to examine the behaviour of Diethylenetriamine Penta Methylene Phosphonic (DETPMP), a commonly used commercial scale inhibitor (SI), when in contact with brine and calcium carbonate (CaCO3). These tests are carried out at pH 2 and pH 4 and at a range of DETPMP concentrations from 0ppm to 5000 ppm. In these tests, the addition of disaggregated CaCO3 to the brine/SI mixture was accompanied by a rise in the pH and a commensurate precipitation of a DETPMP_Ca complex. Apparent adsorption displayed a common 2:1 trend indicating that no adsorption took place, only precipitation. These results changed somewhat when selected divalents (Ca and Mg) were removed from the brine.
Pre-Production Deployed Scale Inhibition Treatments in Deep-Water, West Africa
Authors: Patterson D. , Williams W. , Jordan M. , Douglas R. 
Published: February 2021

Abstract
The injection of seawater into oil-bearing reservoirs in order to maintain reservoir pressure and improve secondary recovery is a well-established, mature operation. Moreover, the degree of risk posed by deposition of mineral scales (carbonate/sulphate) to the injection and production wells during such operations has been much studied. The current deep-water subsea developments offshore West Africa and Brazil have brought into sharp focus the need to manage scale in an effective way.
In a deepwater West African field the relatively small number of high-cost, highly productive wells, coupled with a high barium sulphate scaling tendency upon breakthrough of injection seawater meant not only was effective scale management critical to achieve high hydrocarbon recovery, but even wells at low water cuts have proven to be at sufficient risk to require early squeeze application.
To provide effective scale control in these wells at low water cuts, phosphonate-based inhibitors were applied as part of the acid perforation wash and overflush stages prior to frac packing operations. The deployment of this inhibitor proved effective in controlling barium sulphate scale formation during initial water production eliminating the need to scale squeeze the wells at low water cuts (&lt;10% BS&W). To increase the volumes of scale inhibitor being deployed in the pre-production treatments and so extend the treatment lifetimes scale inhibitor was also added to the frac gel used to carry the frac sand.
This paper outlines the selection methods for the inhibitor chemical for application in frac fluids in terms of rheology, retention/release, formation damage and presents the chemical returns profile from the 5 wells treated (some treatments lasting &gt; 300 days) along with monitoring methods utilized to confirm scale control in the wells treated.
Many similar fields are currently being developed in the Campos basin, Gulf of Mexico, and West Africa, and this paper is a good example of best-practice sharing from another oil basin.
New Insights on the Impact of High Temperature Conditions (176°C) on Carbonate and Sulphate Scale Dissolver Performance
Authors: Jordan Myles M. , Williams Helen , Linares-Samaniego Sandra , Frigo Dario M. 
Published: February 2021

Abstract
Scale-dissolver technology has been developed and applied with varying degrees of success over the past few years to remove carbonate and the more challenging sulphate/sulphide scales from production tubing and process equipment. It can often seem a much safer, more cost-effective remediation approach than physical removal, in particular, in the new generation of HP/HT fields, where any physical well intervention carries high risk, while the high temperatures would normally be beneficial in enhancing scale solubility and dissolution rate.
The current paper reports dissolution characterstics of three solvents for calcite, barite, celestite and anhydrite in the temperature range 85°C to 176° to verify their performance up to the very high temperatures of a specific HP/HT development. These solvents included a typical alkaline-pH chelant for sulphate scale, an organic-acid mixture for carbonate scales, and a novel neutral-pH chelant as a less corrosive solvent for carbonate scale removal. In some tests the liquid-to-solid ratiowasvaried to evaluate the impact of excess scale on solvent performance.
The performance against BaSO4 of the alkaline-pH chelant unexpectedly declines very significantly at 176°C relative to that observed at 85°C. Thermal instability was ruled out as the cause becausethe solvent showed very limited decline in performance when tested at 85°C after it had been thermally aged at 176°C. Performance at 176°C showed an initial rise followed by a decreasein aqueous barium ions, strongly indicating secondary re-precipitation of a barium-containing species at this temperature. In contrast, dissolution rates of carbonate scale by organic acid were greaterat the higher temperature, as would be expected. The novel neutral chelant showed a decline in calcite dissolution performance during the 176°C test but unlike the alkaline-pH chelant used for sulphate scale, this chelant showed degradation after thermal ageing and re-testing at 85°C.
The findings from this paper suggest that there is temperature limit above which effective removal of sulphate scales may not be feasible with the selected solvents due to re-precipitation of a secondary reaction product, while for carbonate removal the current neutral chelants tested have a thermal stability issue at 176°C. These findings need to be considered when evaluating the potential role of chemical remediation in the overall scale-control strategy for HP/HT fields.