Scale Control Strategy Research Articles

Effect of Sulfate-Based Scales on Calcite Mineral Surface Chemistry: Insights from Zeta-Potential Experiments and Their Implications on Wettability.

Scale formation and deposition in the subsurface and surface facilities have been recognized as a major cause of flow assurance issues in the oil and gas industry. Sulfate-based scales such as sulfates of calcium (anhydrite and gypsum) and barium (barite) are some of the commonly encountered scales during hydrocarbon production operations. Oilfield scales are a well-known flow assurance problem, which occurs mainly due to the mixing of incompatible brines. Researchers have largely focused on the rocks’ petrophysical property modifications (permeability and porosity damage) caused by scale precipitation and deposition. Little or no attention has been paid to their influence on the surface charge and wettability of calcite minerals. Thus, this study investigates the effect of anhydrite and barite scales’ presence on the calcite mineral surface charge and their propensity to alter the wetting state of calcite minerals. This was achieved vis-à-vis zeta-potential (ζ-potential) measurement. Furthermore, two modes of the scale control (slug and continuous injections) using ethylenediaminetetraacetic acid (EDTA) were examined to determine the optimal control strategy as well as the optimal inhibitor dosage. Results showed that the presence of anhydrite and barite scales in a calcite reservoir affects the colloidal stability of the system, thus posing a threat of precipitation, which would result in permeability and porosity damage. Also, the calcite mineral surface charge is affected by the presence of calcium and barium sulfate scales; however, the magnitude of change in the surface charge via ζ-potential measurement is insignificant to cause wettability alteration by the mineral scales. Slug and continuous injections of EDTA were implemented, with the optimal scale control strategy being the continuous injection of EDTA solutions. The optimal dosage of EDTA for anhydrite scale control is 5 and 1 wt % for the formation water and seawater environments, respectively. In the case of barite, in both environments, an EDTA dosage of 1 wt % suffices. Findings from this study not only further the understanding of the scale effects on calcite mineral systems but also provide critical insights into the potential of scale formation and their mechanisms of interactions for better injection planning and the development of a scale control strategy.

Identification, surveillance and management of Aedes vexans in a flooded river valley in Nottinghamshire, United Kingdom

Aedes vexans is known to occur in large populations in riverine floodplains in much of Europe, where it can cause a significant biting nuisance and is often subject to large scale control strategies. Until recently it had only been reported in very small numbers in the United Kingdom. After receiving reports of nuisance biting near the river Idle, Nottinghamshire (East Midlands, England), mosquito surveillance was conducted over three years (2018-2020) using Mosquito Magnet adult traps. Ae. vexans was found in all years, in very high numbers, particularly in 2020, reaching a peak of almost 5,000 female mosquitoes per trap night, the highest reported density of trapped adult mosquitoes in the UK. Larval control was conducted in all years, and adult control in one year, however local peculiarities of flood and water management presents challenges and necessitates a multi-faceted approach. Strategies for further expansion of the control operation by developing strategies for water management, coupled with larval surveys to define the extent and seasonality of larval habitats, and application methods of Bacillus thuringiensis israelensis products are discussed.

Two Level Control Strategy for Independent AC/DC Hybrid Microgrid Based on Integrated Control

Aiming at the independent AC/DC microgrid, a simple and effective multi time scale control strategy is proposed by adopting the combination of day ahead scheduling and real-time control. The day ahead scheduling strategy takes the minimum operation cost of AC/DC microgrid as the goal, and schedules the controllable loads in the AC/DC microgrid with particle swarm optimization, which makes full use of renewable energy. The real-time control strategy controls the output of the distributed generation, the load reduction and the switching of the diesel generator according to the real-time energy storage state of charge (SOC), which keep the power balance of the AC/DC microgrid. The effectiveness of the proposed two-level control strategy is verified by a practical AC/DC hybrid microgrid. The results show that the proposed method can make full use of renewable energy and ensure the economic and reliable operation of AC/DC hybrid microgrid.

Laboratory investigation of co-precipitation of CaCO3/BaCO3mineral scale solids at oilfield operating conditions: Impact of brine chemistry

Oilfield mineral scale deposition can become severe flow assurance challenge especially for offshore deepwater productions. Hazards arising from scale formation and subsequent deposition include production system throughput reduction and eventually blockage. Among various types of scales, carbonates are among the most frequently observed scales in oilfield operations. Similar to many natural and industrial processes, co-precipitation of multiple scales can commonly be observed in oilfield operations. Although extensive research efforts have been made in the domain of understanding the thermodynamics of scale formation, there are limited studies to investigate the kinetic aspect of scale formation, particularly the kinetics of co-precipitation of multiple scales. In this study, the kinetic characteristics of CaCO3/BaCO3co-precipitation have been experimentally investigated at representative oilfield conditions of 80 °C and 1 M NaCl condition. The focus was given to the investigation of the impact of different brine chemistry conditions such as mineral saturation level and Ca to Ba molar ratio. The experimental results suggest that CaCO3saturation level, substrate material and molar ratio can impact the nature and morphology of the carbonate scales formed. An elevation of CaCO3saturation index from 0.6 to 2 will change the formed carbonate solids from calcite to aragonite. In addition, at a Ca:Ba molar ratio of 1:15 with an excessive aqueous Ba species available, Ba species can partition into CaCO3crystal lattice to distort CaCO3lattice, resulting in almost 2-fold increase in aqueous Ca concentration. The results and conclusions from this study have the potential to benefit oilfield scale control strategy development, particularly the one related to carbonate scale formation control.

Experimental Evaluation of Attach-and-Release Mineral Scale Control Strategy for Aqueous Fluid Transporting Pipelines

Deposition of mineral scale is a severe operational threat to various industrial facilities, including pipeline and production tubing which are used for transporting aqueous fluid. Chemical inhibit...

A unified time scale intelligent control algorithm for micro grid based on extreme dynamic programming

Benefiting from the progress of power electronics technology, distributed generation technology is developing rapidly. Since micro grids cannot rely on traditional multi-time scale control strategies to ensure the high-quality frequency stability control and economic in the same time scale, this paper proposes an extreme dynamic programming algorithm. The proposed algorithm takes an adaptive dynamic programming algorithm as the framework, an extreme learning machine as a kernel of the evaluation module, a model module, an implementation module and a new prediction module. The resulting unified time scale intelligent control algorithm better realizes the combined functions of droop control + automatic generation control + economic dispatch in the traditional opermode. Finally, in order to verify the effectiveness of the proposed algorithm, a micro grid model of 8 nodes is simulated. The results confirm the feasibility and validity of the proposed extreme dynamic programming algorithm.

The effect of ‘High-pH pretreatment’ on RO concentrate minimization in a groundwater desalination facility using batch air gap membrane distillation

This study compared the efficacy of two different scale control strategies: (i) ‘High-pH pretreatment’; and (ii) antiscalant (AS) addition for reverse osmosis (RO) concentrate minimization, in a lab-scale air gap membrane distillation (AGMD) unit. In contrast with previous studies that used a direct contact membrane distillation set-up, we systematically investigated the performance of batch AGMD configuration with and without the preliminary reduction of scale-forming constituents, using high salinity, high alkalinity, high SiO2 and high magnesium hardness RO concentrate. Results indicated that ‘High-pH pretreatment’ by means of the cold lime-soda ash process was more productive than only AS addition to the RO concentrate, resulting in significant salt precipitation when the concentration factor (CF) in the AGMD system increased above 1.3. The High-pH precipitation process provided significant concentration reduction of SiO2 (96%), magnesium (96%) and calcium (86%). Following ‘High-pH pretreatment’, pH re-adjustment and final AS addition, the use of AGMD allowed us to minimize the existing RO concentrate with an initial total dissolved solids (TDS) level of 10.8 g/L by a CF of 3.2. In addition, this chemical demineralization process enabled operation of the AGMD unit at a higher temperature, thus increasing permeate flux.

Ideal conducting polymer anode for perovskite light-emitting diodes by molecular interaction decoupling

An ideal conducting polymer anode (CPA) in organic and perovskite light-emitting diodes (LEDs) requires high electrical conductivity κ, high work function WF, and prevention of exciton quenching between an anode and an overlying emitting layer. However, increasing the κ and WF at the same time has been a very challenging unsolved issue due to their trade-off relationship: previous approaches to increase the WF have reduced the films’ κ and vice versa. Therefore, delicate molecular scale control of the conducting polymer compositions are required to solve this fundamental issue. Here, we introduce an effective molecular scale control strategy to decouple the WF with κ in a CPA while maintaining blocking capability of exciton quenching. This change resulted in a high current efficiency up to 52.86 cd A−1 (10.93% ph el−1) in green polycrystalline perovskite LEDs. Our results provide a significant clue to develop effective CPAs for highly-efficient organic and perovskite LEDs.

Laboratory evaluation of synergistic effect of transition metals with mineral scale inhibitor in controlling halite scale deposition

Sodium chloride (halite) has been traditionally regarded as an unconventional oilfield mineral scale, compared with more prevalent carbonate and sulfate scales. However, with the increasing productions from offshore deepwater and shale gas fields, halite scale occurrence becomes more frequent, leading to significant technical and financial challenges to productions. Although low-salinity water dilution remains the primary approach in controlling halite scale threat, chemical inhibition has been evaluated as an alternative halite control strategy due to the intrinsic issues associated with low-salinity water availability and water quality. There are limited studies concerning the combined effect of metals, especially transition metals with scale inhibitors in halite control. In this study, the combined effect of a number of transition metal ions with two common halite scale inhibitors was evaluated in a laboratory setup. It was found that among the transition metals studied, Pb2+ ion demonstrates a synergistic effect with the scale inhibitors evaluated by considerably extending the halite induction time. The calculated inhibition efficiency also indicates that the presence of Pb2+ improves inhibitor performance. Although Pb2+ is an environmental pollutant, an aqueous Pb2+ concentration of up to 10 mg L−1 can naturally occur in both natural gas produced water and oilfield produced water. The operators can take advantage of the reported synergistic effect of Pb2+ with scale inhibitors in this study while designing field halite control strategy. The enhanced inhibition efficiency elaborated in this study can be useful in designing the halite scale control strategy, if a decent amount of Pb2+ is present in the produced water.

A novel attach-and-release mineral scale control strategy: Laboratory investigation of retention and release of scale inhibitor on pipe surface

A novel “attach-and-release” approach has been experimentally evaluated as an alternative scale control strategy for pipe flow system. Phosphonate scale inhibitor was initially attached to calcium carbonate medium on the surface of the pipe. Subsequently, the retained inhibitor was released into the flowing fluid for scale control. A plug-flow tube reactor apparatus was adopted in laboratory studies. It shows that formation of calcium-inhibitor precipitate accounts for the attachment of inhibitor and brine chemistry can considerably impact the amount of inhibitor retained. This proposed strategy has the potential to be applied in a pipe flow system to control scale deposition threat.

Control Scheme of a Brushless Doubly Fed Induction Machine for Stand-Alone Generator Systems

The brushless doubly-fed machine (BDFM) is a new type of induction machine which has different structure and operation principle than a conventional AC machine. In this paper, the electromagnetic relation of BDFM is analyzed, and a stand-alone generator system is presented. Based on the analysis, the characteristic and applicability of scale and vector control strategy is build, both of which realize constant voltage output in stand-alone generator systems of variations load.

Composite Fouling on Heat Exchange Surface in Australian Sugar Mill Evaporator

Composite scale of amorphous silica and calcium oxalate is very intractable; it imposes a significant fraction of scale management cost in sugar mill evaporators. This work evaluates silica and calcium oxalate composite fouling using dynamic fouling-loop experiments under different operating conditions with and without sugar. A novel closed-loop setup simulating in a single run the effect of feed concentration in successive stages of evaporation cycle was used. Experiments under constant composition and varying thermal hydraulic effect were conducted. Results indicated synergistic effects for initial silica and calcium oxalate supersaturation values of 2.6 and 1.7. Sugar effects became significant for concentrations in the third effect and above. The fouling mechanism was particulate deposition of silica and calcium oxalate colloidal species strengthened by consolidation; fouling rate increased with decreasing interfacial energy barrier between the surface and foulant, assessed by zeta-potential analysis. Deposit characteristics and deposition rates were concentration and thermal hydraulics dependent. Results confirmed the need that the 5 × 5 (types × stages of fouling) matrix of Epstein needs to be expanded to a 6 × 6 matrix to include composite fouling as a type of fouling. In this study the composite fouling was a surface-controlled process for which the activation energy was similar to typical chemical bond strengths, explaining the role of consolidation in composite fouling. The results contribute to advancement of fundamental understanding of heat exchanger fouling and to development of scale control strategies for composite fouling minimization in sugar mill evaporators.

Reverse Osmosis Desalting of Inland Brackish Water of High Gypsum Scaling Propensity: Kinetics and Mitigation of Membrane Mineral Scaling

The potential for mineral scaling that may limit the generation of new potable water resources by reverse osmosis (RO), from inland brackish water of high gypsum scaling propensity, was experimentally explored via flux decline measurements and real-time RO membrane surface imaging. Antagonistic gypsum and calcium carbonate scaling kinetics were demonstrated for high-sulfate brackish water desalting. RO scaling studies with brackish water from the California San Joaquin Valley (approximately 10 000 mg/L total dissolved solids) revealed that membrane gypsum scaling was increasingly retarded with rising bicarbonate concentrations. Crystal growth rate, fractional membrane scale coverage, and flux decline decreased by up to about 63, 78, and 73%, respectively, as the bicarbonate concentration increased, at the membrane surface, from < 0.01 to 7.81 mM, for a gypsum saturation index of 2. Inhibition of gypsum crystal growth was attributed to bicarbonate adsorption onto the crystal surfaces, and CaCO3 scaling was undetected even up to a calcite saturation index of approximately 16. Given the suppression of gypsum scaling by bicarbonate, it is essential to considerthis effect in the conventional practice of pH adjustment to suppress CaCO3 scaling. The present results suggest that antagonistic and synergistic mineral crystallization kinetics effects are important for optimizing scale-control strategies (e.g., acid and antiscalants addition to the RO feed).

High recovery membrane desalting of low-salinity brackish water: Integration of accelerated precipitation softening with membrane RO

The integration of membrane RO desalting and accelerated precipitation softening (APS) was evaluated for achieving high product water recovery (>95%) from desalting of mildly brackish surface water. A systematic approach that included laboratory RO demonstrations, membrane scaling diagnostics, and mineral solubility analysis was undertaken to develop an effective physical/chemical APS strategy for reducing the concentration of scale-forming ions in the primary RO (PRO) concentrate. APS demineralization, as an inter-stage process, between the PRO and secondary RO (SRO) desalting, involved alkaline pH adjustment and calcite crystal seeding of the PRO concentrate, followed by microfiltration and pH reduction by acid dosing to avoid calcite scaling in the SRO stage. Colorado River water desalting case study demonstrated that, at 90% PRO recovery, the PRO concentrate stream contained barite, calcite, gypsum, and silica above their solubility limits by factors of 122, 47, 1.1, and 0.8, respectively. Further desalting was not feasible with traditional scale-control strategies (e.g., pH reduction and antiscalant addition). However, APS demineralization enabled significant concentration reduction of calcium (>90%), barium (>95%), and strontium (∼78%) and moderate reduction (10–20%) of magnesium and silica. APS kinetics were favorable even in the presence of antiscalant carryover from the PRO stage. The study demonstrated that high recovery desalination of up to 98% is feasible with the PRO-APS-SRO sequence, which reduces the limitations imposed by membrane scaling.

Inter-relationships between corrosion and mineral-scale deposition in aqueous systems

The processes of corrosion and scale deposition in natural and process waters are often linked and this paper considers a number of instances of interactions between the two phenomena. In some circumstances a scale layer (e.g. calcium carbonate) can be advantageously utilised as a corrosion-protection coating on components and this feature has been exploited for many decades in the conditioning of water to induce spontaneous precipitation of a scale layer upon the surfaces of engineering equipment. The electrochemical mechanisms associated with some corrosion and corrosion-control processes can promote alkaline-scale deposition directly upon component surfaces. This is a feature that can be exploited in the operation of cathodic protection (CP) of structures and components submerged in certain types of water (e.g. seawater). Similar phenomena can occur during bi-metallic corrosion and a case study, involving carbon steel/stainless steel couples in seawater, is presented. Additional complexities pertain during cyclic loading of submerged reinforced concrete members in which scale deposition may reduce the severity of fatigue stresses but can be associated with severe corrosion damage to embedded reinforcing steel. Also considered are scale-control/corrosion interactions in thermal desalination plant and an indirect consequence of the scale-control strategy on vapourside corrosion is discussed.

Predicting Brine Mixing Deep Within the Reservoir and Its Impact on Scale Control in Marginal and Deepwater Developments

SummarySulphate scale deposition is a common problem in hydrocarbon reservoirs in which injection seawater that is rich in sulphate mixes with formation brines that are rich in barium, strontium, and calcium. Deposition of these scales can cause significant production impairment if it occurs within zones near the production wellbores. To control scale deposition in the near-wellbore region of a reservoir, scale squeeze treatments are commonly deployed. In cases in which scale severity is very high, removal of sulphate ions from the injection water is an alternative scale-control strategy. Both these mitigation methods have associated capital (CAPEX) (e.g., desulphation plant) and operating expenditures (OPEX) (e.g., scale squeeze treatments).To assess the severity of the problem in new fields, thermodynamic calculations typically are performed to calculate the mass of scale that will form. Until recently, little work has been carried out to identify the location of scale formation within the reservoir. In this paper, field data and flow simulations from three North Sea fields are presented to show that scale formation can, in fact, occur deep within the reservoir and can have a negligible negative impact on oil production in the near-wellbore region.Evidence is presented from these North Sea fields that shows the evolution of the brine chemistry as seawater breakthrough occurs and as squeeze treatments are applied. The evidence from the produced brine chemistry is linked to flow calculations for these fields to show that in some systems scale is depositing deep within the reservoir, reducing the potential for damage in the near-production wellbore region. The extent and impact of the deposition varies throughout the reservoir and can be quantified. Modeling brine mixing and stripping of the scaling ions before the fluids reach the production wellbore has a significant impact on the economic assessment of marginal fields and deepwater developments. In such fields, the technical challenge and cost (CAPEX/OPEX) of scale control might make development uneconomical. This paper outlines the data requirements and methodology used to allow such an assessment to be made.

Advantages of a New Chemical Delivery System for Fractured and Gravel- Packed Wells

Summary The deposition of scale, such as carbonates and sulphates, in production facilities represents a serious operational problem that can result in significant well productivity decline. Current scale control strategies can involve significant capital and operational expenditure. Development work, involving laboratory testing and a field trial, has demonstrated the technical benefits of a revolutionary method of downhole scale inhibitor delivery that can prevent scale deposition for a significant proportion of a well's lifetime. The method involves the slow release of scale inhibitor from porous proppants. Economic analysis indicates that significant benefits can be derived for a variety of field development and well completion types. The greatest economic benefits would be realized for subsea and minimum facility installations with high intervention costs, where squeeze delivery of inhibitor or mechanical workover are used for scale control. In addition, major economic benefits can be realized for horizontal wells with unfavorable pressure regimes, multilateral-type completions, multiple fractured wells, and many conventional completion types. The new chemical delivery method offers cost reduction through reduced deferred oil, efficiency of chemical usage, and fewer workovers using coil tubing and intervention vessels. Economic analysis has indicated that for some conventional and advanced well types, fracturing a well and deploying proppant impregnated with scale inhibitor, is economically preferable to a conventional strategy of squeeze treatment in an unfractured well. An additional economic benefit of proppant impregnated with scale inhibitor is increased well productivity. The benefit is derived from the combined effect of improved gel breaking, and scale inhibition during well cleanup. This has been demonstrated in laboratory testing and would appear to be confirmed by field observations. A further benefit of applying scale inhibitor as chemically impregnated proppant is the immediate treatment of produced water when water breakthrough occurs. This feature avoids the formation damage that can occur before squeeze treatment mobilization. In addition, for some applications involving large fractures there is the potential for lifetime well treatment. This paper describes the laboratory work, the field trial, and the economic benefits of the new product.

Research directions in solids deposition in geothermal systems

The closing session of the International Workshop on the Deposition of Solids in Geothermal Systems consisted of the formation of special interest working groups to discuss future research directions in the fields of carbonate deposition, silica scale, sulfide deposition, treatment methodologies, heat exchanger engineering, and water/rock reactions. Recommendations made by the working groups for future research included the following: development of more complete and accurate models of the physical and chemical mechanisms associated with the nucleation, adhesion, and growth of scale minerals onto substrate surfaces; investigation and synthesis of more efficient and cost effective chemical scale inhibitors; improvements in heat exchanger materials, design, and operational characteristics; and development of more general economic models for heat extraction facilities that will allow an evaluation of the costs and benefits of various scale-control strategies.

A Calcium Carbonate Scale Inhibitor for Direct-Contact Binary Geothermal Service

Auerbach, Michael H.; Pfizer Central Research Pfizer Central Research Reimer, Robert A.; Pfizer Central Research Pfizer Central Research Olander, Robert G.; Barber-Nichols Engineering Co. Rapier, Pascal M.; Lawrence Livermore Natl. Laboratory Summary A 500-kW direct-contact binary-cycle pilot geothermal power plant was constructed and successfully operated power plant was constructed and successfully operated free of scale at the U.S. DOE East Mesa geothermal test facility. The pilot plant used an Elgin tower direct-contact heat exchanger (DCHX) with isobutane as the working fluid. Initial tests with the untreated 340 deg. F (170 deg. C) geothermal brine gave heavy calcium carbonate fouling of the brine boost pump, flow monitors, and flow-control valves within 20 to 50 hours of startup. Use of 2 ppm high-temperature polymeric scale inhibitor in the feed brine enabled plant operation for more than 700 hours without formation of detrimental scale. The antiscalant was not extracted into the working fluid and did not emulsify the hydrocarbon/brine interface. On the basis of dosage and flow, the additive cost was calculated to be about 0.06 cents per net kW-hr of power generated. Introduction Electrical power is generated from liquid-dominated geothermal resources either bydirect flash of the hot brine to produce steam that drives a turbine ortransfer of sensible heat from the brine to a more volatile working fluid in an organic Rankine cycle loop without brine flash. The vaporized working fluid, usually a low-boiling-point hydrocarbon, drives the power turbine in this binary-cycle process. Heat is transferred from the geothermal brine to the binary-cycle working fluid in either a surface-type tube-and-shell heat exchanger or a DCHX, where the brine and working fluid mix together. The higher effective surface areas and heat-transfer coefficients obtainable with direct contact greatly reduce the capital cost for a given heat flux. However, extraction of steam and noncondensible gases into the working fluid increases turbine backpressure and reduces power output and working fluid recovery, making the DCHX process more complex to operate economically. The direct-flash process is generally more efficient for resources above 392 deg. F (200 deg. C); the binary-cycle process is favored below this temperature. Both processes process is favored below this temperature. Both processes can he completely interrupted or severely restricted by heavy mineral scaling, which fouls or plugs surface piping, pump impellers, and reinjection wellbores. The piping, pump impellers, and reinjection wellbores. The scaling minerals most often found are silica, heavy metal sulfides, and calcium carbonate, depending on the temperature and total dissolved salt content of the particular brine. Scale-control strategy thus depends on the particular brine. Scale-control strategy thus depends on the type of scale, its seventy, and the details of the plant process. process. In 1978 the U.S. DOE commissioned Lawrence Berkeley Laboratory to build and demonstrate a 500-kW direct-contact binary-cycle geothermal pilot plant. Design, construction, and operation of the plant were subcontracted to Barber-Nichols Engineering Co. The plant was built and tested at the U.S. DOE East Mesa plant was built and tested at the U.S. DOE East Mesa geothermal test facility in the Imperial Valley, Holtville, CA, during 1979–81. Extended operation of this plant was severly hampered by CaCO3 scaling. JPT P. 1546