Flow Assurance

Flow assurance involves a cost-effective approach to produce and transport fluids from the reservoir to a processing facility. During production and transportation of crude oil, knowledge of fluid properties and operating conditions is critical to preventing formation and deposition of undesired solids (e.g. hydrates, wax, asphaltenes, and scales). In cases of extreme temperatures and pressures, it is possible that methane gas hydrates crystallize or asphaltenes precipitate in the pipeline. If not properly controlled, the hydrate crystals, asphaltene, or wax particles may precipitate and agglomerate to the point of plugging the pipeline. Removal of a hydrate or asphaltene plug in a subsea pipeline can be very expensive and dangerous.

Flow assurance challenges are further mounting due to the transition from conventional oil reserves to mature oil fields. As oil fields mature, water fraction increases. In some cases, operators inject water in mature oil fields to enhance oil recovery. Water-in-crude-oil emulsions further complicate flow assurance strategies. The presence of formation or injection water along with calcium carbonate can lead to scaling under certain conditions. Calcium carbonate scaling can block the pipeline and foul production equipment further making mature oil fields less profitable. Most of the commercially available hydrate inhibitors anti-agglomerants become less effective as water cut increases. Eventually the emulsion needs to be broken to separate oil and water. Breaking emulsions via physical or chemical methods can be very costly, especially for heavy oil emulsions that contain emulsion-stabilizing solids such as asphaltenes.

Therefore, it is critical to study and develop cost-effective flow assurance strategies to take control of solids and emulsions to minimize economic risks over the life of an oil field.

Multiphase pipeline flow often occurs under extreme temperature and pressure making offline sampling and analysis difficult or impossible. Offline samples are often manipulated through dilution or dispersion which can alter multiphase components. Offline measurements often cannot be applied to make real-time process optimization and control decisions. With the advent of in situ particle characterization technology, such as ParticleTrack and ParticleView, one can quickly measure the particle phase behavior in situ - without pulling samples.

Flow assurance applications include:

• Asphaltene Precipitation
• Gas Hydrate Formation
• Emulsion Separation
• Wax Appearance Temperature and Wax Crystal Morphology

Asphaltenes are complex mixtures of polyaromatic compounds with heteroatomic species such as nitrogen, oxygen, and sulphur along with organometallics such as iron, nickel, and vanadium. Asphaltenes are typically described as the fraction of crude oil insoluble in alkanes (e.g. n-heptane or n-pentane) but soluble in aromatic solvents (toluene or benzene). Changes in crude oil composition, pressure, and temperature conditions can destabilize asphaltenes. For example, pressure depletion during crude oil production can lead to undesired asphaltene precipitation and deposition in wellbore and reservoirs. Asphaltene precipitation/deposition leads to formation damage, stable emulsions difficult to separate, and partial/complete plugging of the pipeline.

Asphaltene precipitation depends on several parameters, including temperature, pressure, and fluid composition. Similarly, asphaltene deposition in a pipeline can depend on flow rate, interaction between the particles, interaction between the particles and pipe surface, etc. 

Onset ratio and asphaltene precipitation kinetics were studied for four crude oils and a 190+ residue. 40 g of crude oil was placed in a glass beaker and agitated at 400 rpm. ParticleTrack
was used to study onset, kinetics and endpoint for asphaltene  precipitation as n-heptane was added.

• ParticleTrack rapidly determines the onset ratio for different crude oils - with no sampling required
•  Three commercial additives - A, B and C - were added to the D-190+ residue at different ppmV concentrations
• ParticleTrack was used to quickly screen the most suitable additive type and concentration to inhibit asphaltene precipitation
• By studying these kinetic effects, scientists can understand and control asphaltene precipitation and deposition for crude oils from various sources

Reference: Dufour et. al. Energy Fuels, 2009, 23 (3), 1155-1161.

Presented with FMC and the University of Tulsa, this in-depth presentation covers industry examples of optimization in flow assurance, separations, fouling, and tailings management to reduce exploration and production costs in dark crude oil at standard operating temperatures and pressures, without sampling or sample dilution.

Gas hydrates are ice-like crystalline structures formed via complex interaction between oil, gas, and water under high pressure and low temperature. Fundamental knowledge about structural transitions, formation mechanism, and formation kinetics are still unclear for gas hydrates.

Natural conditions necessary for gas hydrate crystallization frequently occur in petroleum pipelines. After hydrate particles nucleate, hydrate growth and agglomeration occurs. These agglomerates can eventually become large enough to create a hydrate plug in the pipeline. Formation of the hydrate plug adversely affects fluid flow, in some extreme cases even complete blockage of the pipeline. Hence, gas hydrate formation have costly implications due to interrupted production via flow restriction or plugging, equipment damage, and safety risks to operators.

Thermodynamic inhibitors (THI) are industry standards for hydrate prevention despite high cost, environmental concerns, and high operating. Alternatively, less expensive "Low Dosage Hydrate Inhibitors" (LDHI) can extend induction time or prevent agglomeration of primary hydrate particles and maintain a transportable slurry. In order to develop new, cost-effective strategies to manage the hydrates rather than completely prevent their formation, it is critical to develop sound understanding of hydrate crystallization, agglomeration, and deposition mechanisms.

Using reliable in situ technologies to monitor real time hydrate crystallization and agglomeration will enable operators to i) optimize the use of expensive THI, ii) evaluate the reliability of less expensive LDHI, and iii) develop robust strategy utilizing both THI and KHI.

ParticleView visualizes significant hydrate agglomeration in situ with no LDHI (left image). Use of LDHI stabilizes hydrates into a well-dispersed mixture (right image).

Reference: Duy Nguyen et. al. (Nalco and METTLER TOLEDO collaboration)

Probe-based ParticleTrack and ParticleView technologies are ideal for characterizing methane gas hydrates, asphaltene particles, scales, and oil emulsions. In most cases, the conditions (high pressure) in which hydrate crystals form and asphaltenes precipitate make them extremely difficult to sample. The particle and droplet systems are extremely sensitive to temperature and pressure fluctuations. Additionally, offline techniques require that the samples be diluted, which can alter droplet size, reverse hydrate agglomeration, and solubility of asphaltenes. Even under the conditions when sampling is possible, the measurement of dilute samples is not representative of the actual system and provides a very limited data set. With FBRM and PVM probe technologies, the researcher can track the entire dynamic particle and droplet system in crude oil at standard operating temperatures and pressures, without sampling or sample dilution.

Desalting is an important step prior to crude oil refining during which inorganic salts and contaminants in crude oil are transferred to water phase and removed. Poor desalter performance leads to fouling of refinery equipment due to carryover of solids, corrosion of crude tower from acid formation, and increased cost of brine effluent treatment due to oil under-carry.

ParticleTrack is highly sensitive to changes in droplet count and dimension as agitation is varied – increased agitation leads to decreased mean and increased population of small droplets (<80 μm).

• Optimum droplet dimension and population directly impact contaminant transfer to water phase during mixing stage and oil-water separation in holding tanks.
• ParticleTrack trends immediately identify critical process parameters (e.g. mixing, wash water flow) and enable control of process parameters to maximize contaminant extraction and minimize separation time.

High-resolution ParticleView images confirm transformation of large droplets at 500 rpm to smaller droplets at 200 rpm.

ParticleTrack chord length distribution for each agitation rate, enabling operations to target droplet distribution to improve desalter performance.

Information derived from ParticleTrack and ParticleView process tools help reduce solids carryover/oil under-carry, optimize chemical additive usage, speed up desalter operation, and subsequently prevent costly desalter upsets such as corrosion and fouling.

Demulsifier for oil-water separation is often evaluated using bottle test - a visual technique blind to droplet size and emulsion characteristics. In this study, ParticleTrack and ParticleView probes were used to monitor the effect of demulsifier on 30 % oil (API ~30) + 70 % brine mixture.

a. t= 15 m: In the absence of demulsifier, real-time ParticleView images show emulsion remains stable for the experimental duration of 15 minutes. ParticleView probe helps in quick visual confirmation of emulsion stability/instability.

b. t= 0 m: In the presence of demulsifier initially larger droplets are observed. Droplets are seen in situ in their natural environment without affecting physical integrity of droplets via sampling.

c. t= 3 m Over time, smaller droplets coalesce and undergo morphological rearrangement to form larger droplets. ParticleView tracks droplet evolution in real time, providing key information on droplet dynamics and transformation in the presence of demulsifier.

d. t = 6 m Finally, large droplets separate, leaving behind small oil droplets in brine. In situ ParticleView images can be used to quickly assess the leanness of oil and water phase after the separation.

ParticleTrack distributions quantify changes in droplets in the presence of demulsifier. Droplet dimension directly impacts oil- water separation process – quantification of droplet dimension enables rapid screening/design of effective demulsifier

• Understanding the effect of demulsifier for oil water separation is crucial in saving cost of petroleum transportation and refining
• Inline monitoring provides a direct method to monitor processes by precisely tracking changes in emulsion and formulating optimum demulsifier to achieve faster and easier oil-water separation

Reference: Duy Nguyen et. al. (Nalco and METTLER TOLEDO collaboration)

ParticleView and ParticleTrack have been used in Flow Assurance for oil and gas production by leading companies and research groups. Discover a selection of references below.

Gas Hydrate Formation

Aline Melchuna, Ana Cameirão, Yamina Ouabbas, Jean-Michel Herri, Philippe Glenat. Transport of hydrate slurry at high water cut. The 8th International Conference on Gas Hydrates, Jul 2014, Pékin, China. pp.T5-16, 2014.

Greaves  D,  Boxall  J,  Mullingan  J,  Sloan  ED, Koh  CA.   Hydrate  Formation  from  High  Water Content-Crude Oil  Emulsions .  Chemical Engineering Science, vol. 63. 2008. p. 4570-4579.

Turner D,  Miller K, & Sloan E. Direct conversion of water droplets to methane hydrate in crude oil. Chemical Engineering Science, 2009 vol: 64 (23) pp: 5066-5072. 10.1016/j.ces.2009.08.013

Asphaltenes

Marugán J,  Calles J,  Dufour J,  Giménez-Aguirre R,  Peña J, &  Merino-García D. Characterization of the Asphaltene Onset Region by Focused-Beam Laser Reflectance: A Tool for Additives Screening. Energy & Fuels. 2009 vol: 23 (3) pp: 1155-1161. 10.1021/ef800626a.

Ruidiaz EM, Koroishi ET, Kim NR, Trevisan OV, Soares-Bassani G & Merino-Garcia D. Evaluation of Asphaltene Deposition - A Systematic Study and Validation of Online Focused Beam Reflectance Measurement FBRM® at Reservoir Conditions. J Pet Environ Biotechnol 2018, Vol 9(2): 364.  DOI: 10.4172/2157-7463.1000364

Javier Dufour, José A. Calles, Javier Marugán, Raúl Giménez-Aguirre, José Luis Peñaand Daniel Merino-García. Influence of Hydrocarbon Distribution in Crude Oil and Residues on Asphaltene Stability. Energy Fuels, 2010, 24 (4), pp 2281–2286. DOI: 10.1021/ef900934t.

Oil-Water Emulsions

Boxall J,  Koh C,  Sloan E,  Sum A,  Wu D. Measurement and Calibration of Droplet Size Distributions in Water-in-Oil Emulsions by Particle Video Microscope and a Focused Beam Reflectance Method. Industrial & Engineering Chemistry Research, 2010 vol: 49 (3) pp: 1412-1418. DOI10.1021/ie901228e.

Less S, &  Vilagines R. Light beam reflectance measurement of droplets diameter distribution in crude oil emulsions, Fuel, 2013 vol: 109 pp: 542-550. DOI10.1016/j.fuel.2013.03.048.

Wang W,  Li K,  Wang P,  Hao S,  Gong J. Effect of interfacial dilational rheology on the breakage of dispersed droplets in a dilute oil–water emulsion. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2014 vol: 441 pp: 43-50. DOI10.1016/j.colsurfa.2013.08.075.

Scale

N. Al Nasser, Waleed & Pitt, Kate & J. Hounslow, Michael & D. Salman, Agba. (2013). Monitoring of aggregation and scaling of calcium carbonate in the presence of ultrasound irradiation using focused beam reflectance measurement. Powder Technology. 238. 151–160. 10.1016/j.powtec.2012.03.021.

N. Al Nasser, Al Salhi F. Scaling and aggregation kinetics determination of calcium carbonate using inline technique. Chemical Engineering Science, 2013 vol: 86 pp: 70-77. 10.1016/j.ces.2012.05.018

Rosário, F.F.,MONTALVÃO, V.T.K., PEREIRA, M.L.O., &  J. F. CAJAIBA DA SILVA (2012) Kinetic Study of Calcium Carbonate Precipitation by Using Real Time FTIR and FBRM Analyses. 13th International Conference on Petroleum Phase Behavior and Fouling, Saint Petersburg, Florida.