Micromechanical Force Research Articles

Study Evaluates Hydrate Antiagglomerants

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28578, “Quantitative Ranking and Development of Hydrate Antiagglomerants,” by Shane A. Morrissy, Temiloluwa O. Kuteyi, Mike L. Johns, Eric F. May, SPE, and Zachary M. Aman, SPE, University of Western Australia, and Stuart F. McKay, SPE, Woodside Energy, prepared for the 2018 Offshore Technology Conference Asia, Kuala Lumpur, 20–23 March. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission. A common hydrate-management strategy involves the use of large volumes of thermodynamic inhibitors (THIs) to operate outside the hydrate-stability region. However, this strategy represents significant capital expenditure and operating costs. Low-dosage hydrate inhibitors (LDHIs), in the form of kinetic hydrate inhibitors (KHIs) and antiagglomerants (AAs), present an economical alternative to THIs. In this study, a quantitative micromechanical force (MMF) has been deployed to study the performance of seven industry AAs. The results illustrate that an effective AA is one that lowers the cohesive forces between hydrate particles. Introduction AAs prevent hydrate agglomeration of a steady-state hydrate slurry. Hydratephilic AAs are surfactants that adsorb to the hydrate/oil interface in preference to the water/oil interface. Current operating experience suggests that AAs may be unsuited to the high water cuts that are characteristic of late field life. A successful hydrate AA lowers the cohesive force or surface free energy of hydrate particles to prevent agglomeration. Rocking cells and high-pressure visual autoclaves provide a semiquantitative assessment of hydrate blockage. However, a knowledge gap exists with regard to whether current industry AAs actually lower hydrate interparticle cohesive and surface free energy. Techniques to deconvolute the mechanism of the action of AAs are required to better understand how AAs affect hydrate blockage. Experimental Procedure Micromechanical Hydrate Cohesive Force. A third-generation MMF apparatus was used to measure the cyclopentane hydrate interparticle cohesive force. The MMF uses cyclopentane to create Structure II cyclopentane hydrates, the same hydrate structure present in the field. The cohesive-force-measurement technique was adapted from previous re-search on hydrate cohesion and asphaltene cohesion. Interfacial Tensiometry. An optical interfacial tensiometer was used to measure the interfacial tension (IFT) between water and oil phases at ambient pressure and room temperature. A hooked needle with the AA prepared in paraffin oil was placed in a bulk phase of deionized water. The resolution of this apparatus is typically +- 1 mN/m and the threshold sensitivity is 1 mN/m. Typically, surfactant-free systems will rap-idly reach equilibrium within 1 minute of creating an oil droplet in water. Conversely, the presence of a surfactant may decrease the IFT as a function of time, asymptotically approaching a steady-state value. Because the AAs studied contain surfactant functionality, each IFT was measured for at least 20 minutes, after which point the IFT was not observed to change with time. Each data point represents an average of at least four independent trials.

The effect of NaCl concentration and corrosion on cohesion/adhesion forces of structure-II hydrate particles

Gas hydrates are ice-like solid compounds formed from water and suitably sized gas molecules under high pressure and low temperature conditions. In typical oil and gas transportation flowlines, when water is present gas hydrates particles can form, agglomerate, and accumulate in the flowlines. These particles can also deposit on flowline walls during fluid flow or during shut-in/restart conditions. The formation of hydrate plugs can cause a blockage in the flowline, as well as other safety concerns. Although researchers have studied how temperature and annealing time would affect the cohesion/adhesion forces between hydrate particles and particle-surface systems, the effects of surface corrosion, salinity and water amount on the adhesion force have not been reported. Deep-water flowlines typically contain brine, and water condensation and corrosion can occur on flowline walls. A water layer and corrosion on flowline walls can affect hydrate film growth and deposition, and salt dissolved in the liquid phase may also influence the agglomeration of hydrate particles. Thus, the effects of free water, corrosion and salt on CH4/C2H6 hydrate particle-particle and particle-surface micromechanical forces are essential for advancing the understanding on hydrate agglomeration and deposition mechanisms in gas dominated deep-water pipelines. In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force (MMF) apparatus was applied to directly measure CH4/C2H6 hydrate adhesion/cohesion forces. The influence of NaCl concentration on the cohesion force between CH4/C2H6 hydrate particles was studied, and the effect of surface corrosion on adhesion forces between hydrate particles and carbon steel (CS) were analysed. It was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model. For the adhesion force measurements, the results indicated that with increasing visual corrosion, the adhesion force between gas hydrate particle and CS surface increased by up to 500%.

Effects of a naturally derived surfactant on hydrate anti-agglomeration using micromechanical force measurement

The performance of a hydrate anti-agglomerant (AA) on cyclopentane (CyC5) hydrate anti-agglomeration at various concentrations (0–1wt%, based on the oil phase) using MMF apparatus has been investigated. At low AA concentrations up to 0.01wt%, the AA reduces the cohesion force (capillary force) by reducing the CyC5-water interfacial tension. At concentrations higher than 0.1wt%, hydrate hydrophobicity alternation and AA’s thermodynamic inhibition effects are the main part of AA’s mechanism. Additionally, a “temporary agglomeration” phenomenon caused by surface melting of the hydrate particles is also observed, which may indicate the AA’s weak ability to produce stable water-CyC5 interface.

An analytical model of burnishing forces using slab method

During the processing of material by burnishing operations, tangential and normal forces play a key role in determining the burnished surface quality, surface hardness, fatigue life, and state of residual stress. However, prediction of the burnishing force in major portions of the paper was based on the micromechanical force model on surface asperities that contain many simplifications and makes the understanding of the model quite complex. In the present work, an analytical study has been carried out to predict the ball burnishing forces in the tangential and normal directions. Firstly, 2D geometrical model of the process was developed to identify the acting forces and their relevant directions during burnishing. Then the forces were related to the burnishing pressure that is calculated by the slab method analysis. The obtained results were further verified by experimental trials. In addition, the developed models were used to analyze the effect of burnishing input variables such as feed rate, burnishing depth, ball radius, and friction coefficient on the forces. Results indicated that the experimental observations are in good agreement with the developed model. Hence, it can be significantly used to predict the forces acting during burnishing and it can provide comprehensive understanding of the effect of process factors on burnishing forces.

Interfacial Properties and Mechanisms Dominating Gas Hydrate Cohesion and Adhesion in Liquid and Vapor Hydrocarbon Phases.

The interfacial properties and mechanisms of gas hydrate systems play a major role in controlling their interparticle and surface interactions, which is desirable for nearly all energy applications of clathrate hydrates. In particular, preventing gas hydrate interparticle agglomeration and/or particle-surface deposition is critical to the prevention of gas hydrate blockages during the exploration and transportation of oil and gas subsea flow lines. These agglomeration and deposition processes are dominated by particle-particle cohesive forces and particle-surface adhesive force. In this study, we present the first direct measurements on the cohesive and adhesive forces studies of the CH4/C2H6 gas hydrate in a liquid hydrocarbon-dominated system utilizing a high-pressure micromechanical force (HP-MMF) apparatus. A CH4/C2H6 gas mixture was used as the gas hydrate former in the model liquid hydrocarbon phase. For the cohesive force baseline test, it was found that the addition of liquid hydrocarbon changed the interfacial tension and contact angle of water in the liquid hydrocarbon compared to water in the gas phase, resulting in a force of 23.5 ± 2.5 mN m-1 at 3.45 MPa and 274 K for a 2 h annealing time period in which hydrate shell growth occurs. It was observed that the cohesive force was inversely proportional to the annealing time, whereas the force increased with increasing contact time. For a longer contact time (>12 h), the force could not be measured because the two hydrate particles adhered permanently to form one large particle. The particle-surface adhesive force in the model liquid hydrocarbon was measured to be 5.3 ± 1.1 mN m-1 under the same experimental condition. Finally, with a 1 h contact time, the hydrate particle and the carbon steel (CS) surface were sintered together and the force was higher than what could be measured by the current apparatus. A possible mechanism is presented in this article to describe the effect of contact time on the particle-particle cohesive force based on the capillary liquid bridge model. A model adapted from the capillary liquid bridge equation has been used to predict the particle-particle cohesive force as a function of contact time, showing close agreement with the experimental data. By comparing the cohesive forces results from gas hydrates for both gas and liquid bulk phases, the surface free energy of a hydrate particle was calculated and found to dominate the changes in the interaction forces with different continuous bulk phases.

Effects of sorbitan monooleate on the interactions between cyclopentane hydrate particles and water droplets

ABSTRACTThe effects of a typical anti-agglomerant, sorbitan monooleate (Span80), on the interactions between cyclopentane (CyC5) hydrate particles and water droplets were investigated using a micromechanical force (MMF) apparatus. The concentration of Span80 in CyC5 was ranged from 0.01 wt% to 1 wt%, and the experimental temperature was set at 1.5°C and 7°C, respectively. The results indicate that the absorption of Span80 on the droplet surface can render the interfaces more stable, preventing hydrate agglomeration. When the preload/contact force exceeds the strength of the interface (< ∼ 10 µN), the droplet ruptures, and the subcooling influences the interaction behavior significantly. At the lower temperature (1.5°C), the water droplet can spontaneously spread over the whole hydrate particle due to the significant reduction in water–CyC5 interfacial tension, and the water converts into hydrate rapidly. In this case, Span80 actually accelerates the agglomeration process and grants much shorter time to allow the external force to separate the water droplet and hydrate particle. At the higher temperature (7°C), the capillary bridge dominates the interaction behavior. The addition of Span80 reduced the capillary force through reducing the water–CyC5 interfacial tension. The measurements and observations in the present work can provide new insights into the mechanism of Span80 on inhibiting hydrate agglomeration.

Reduction of Clathrate Hydrate Film Growth Rate by Naturally Occurring Surface Active Components

During the production of offshore oil and gas, the cooling of hydrocarbons toward seafloor temperatures enables the formation of gas hydrates, which may restrict fluid flow and ultimately block the flowline. During the formation of a hydrate blockage, a hydrate film may grow between individual particles or between hydrate particles and the pipeline wall, respectively, resulting in a higher slurry viscosity or a reduced hydraulic diameter. This hydrate film growth rate has been previously studied as a function of pressure, temperature, and hydrate guest species, but limited data are available to guide whether naturally occurring surface active components in the oil may affect the hydrate film growth rate. In this study, we have used a micromechanical force (MMF) apparatus to quantify the film growth rate of cyclopentane hydrate at moderate subcooling. Naturally occurring surface active species were obtained from an Australian crude oil by solvent extraction to separate out asphaltenes, binding resins, and ...

Experimental Investigation on the Interaction Forces between Clathrate Hydrate Particles in the Presence of a Water Bridge

The agglomeration of hydrate particles is one of the main causes of hydrate accumulation or bedding in oil and gas pipelines. The unconverted water droplets in the system play a crucial role in hydrate particle agglomeration. In this study, a novel technique was developed to directly measure the interaction forces between cyclopentane hydrate particles with a water bridge between them using a micromechanical force apparatus. On the basis of the developed method, the interaction forces at different temperatures and water bridge volumes and the effects of mineral oil were experimentally studied. At a low subcooling level of 1.7 °C, the contact areas and adhesion forces between the hydrate particles and water droplets increased with the increase in the water droplet volume. For the case of a higher subcooling level of 6.2 °C, rapid hydrate formation between the bridging water droplets prevented the hydrate particles from being effectively wetted, resulting in a small contact area. There was no clear relation...

High pressure micromechanical force measurements of the effects of surface corrosion and salinity on CH4/C2H6 hydrate particle-surface interactions.

In order to investigate the mechanism of gas hydrate deposition and agglomeration in gas dominated flowlines, a high-pressure micromechanical force (MMF) apparatus was applied to directly measure CH4/C2H6 hydrate adhesion/cohesion forces under low temperature and high pressure conditions. A CH4/C2H6 gas mixture was used as the hydrate former. Adhesion forces between hydrate particles and carbon steel (CS) surfaces were measured, and the effects of corrosion on adhesion forces were analyzed. The influences of NaCl concentration on the cohesion force between CH4/C2H6 hydrate particles were also studied for gas-dominated systems. It was observed that there was no measurable adhesion force for pristine (no corrosion) and corroded surfaces, when there was no condensed water or water droplet on these surfaces. With water on the surface (the estimated water amount was around 1.7 μg mm-2), a hydrate film growth process was observed during the measurement. CS samples were soaked in NaCl solution to obtain different extents of corrosion on surfaces, and adhesion measurements were performed on both pristine and corroded samples. The adhesion force was found to increase with increasing soak times in 5 wt% NaCl (resulting in more visual corrosion) by up to 500%. For the effect of salinity on cohesion forces, it was found that the presence of NaCl decreased the cohesion force between hydrate particles, and a possible explanation of this phenomenon was given based on the capillary liquid bridge model.

Competitive Interfacial Effects of Surfactant Chemicals on Clathrate Hydrate Particle Cohesion

In oilfield production conditions, many chemicals are present in the form of natural surfactants that occur in the oil phase as well as additives that are injected to control the properties of the liquid phases. These additives may include low-dosage hydrate inhibitors, such as kinetic hydrate inhibitors or anti-agglomerants, corrosion or scale inhibitors, dispersants, emulsifiers, etc. To achieve slurry flow in subsea oil flowlines, the agglomeration of hydrate particles must be minimized so that small, dispersed hydrate particles are transportable rather than forming larger aggregates that may plug the flowline. While many compounds that are present in flowlines are known to affect the cohesion force between hydrate particles, each chemical is often studied separately, where no other additives are present. This study focuses on classifying the possible interactions of different classes of chemicals from the cohesion force between hydrate particles. A micromechanical force apparatus was used to measure t...

Micromechanical Interactions between Clathrate Hydrate Particles and Water Droplets: Experiment and Modeling

The micromechanical interactions between hydrate particles and unconverted water droplets play an important role in determining hydrate agglomeration, which is a key cause of hydrate blockages. In this study, the interaction behaviors between cyclopentane hydrate particles and water droplets in different conditions were directly investigated using a micromechanical force apparatus. For a smaller extent of subcooling, no hydrate was visibly converted from the water droplet during the measurement. A modified theoretical model was proposed to predict the corresponding interaction behavior. A parabolic approximation was found to be adequate for describing the liquid bridge shape. The insignificant change in the interfacial area between the liquid and the hydrate as the separation distance varied suggests the presence of a strong wetting hysteresis between liquid bridges and hydrate particles. The capillary force model can predict the interaction force with satisfactory accuracy. At a higher level of subcoolin...

Cyclopentane hydrate cohesion measurements and phase equilibrium predictions

Clathrate hydrates can form in oil and gas flowlines at high pressures and low temperatures. These solids frequently form under flowing conditions, where they can encounter other hydrate particles due to turbulent mixing. Hydrates may also form in locations where they can anneal significantly before coming in contact with other hydrate particles, such as during transient shut-in conditions in a flow line. Understanding the effect of different shut-in/annealing time periods on hydrate cohesive forces can be important in providing further insight into effective strategies to prevent hydrate plug formation.Cyclopentane hydrates were tested using a micromechanical force (MMF) apparatus to investigate the effect of annealing time on the cohesive forces between hydrate particles. Annealing time was found to reduce the cohesion force between particles at various temperatures tested. This was attributed to the reduction of micropores that connect the unconverted water center of the hydrate to the exterior shell, reducing the water layer available for cohesion.In order to further understand these systems, an understanding of the thermodynamic phase equilibria for systems containing cyclopentane is needed. The prediction capability of the in-house hydrate phase equilibria prediction tool (CSMGem) was therefore improved by optimizing the Kihara potential parameters for cyclopentane using pure and mixed cyclopentane hydrate phase equilibria experimental data. The optimized set of Kihara parameters was then used to predict the gas hydrate phase boundary as well as the fractional cage occupancy of guest molecules, where the larger cavities of structure II were confirmed, as expected, to be filled only by cyclopentane molecules.

Micromechanical Cohesive Force Measurements between Precipitated Asphaltene Solids and Cyclopentane Hydrates

Asphaltenes are the heaviest and most polar class of compounds in crude oil, which may precipitate out of solution due to changes in the pressure, composition, or temperature. During production, aggregation between asphaltene solids may lead to viscosification of the oil phase and/or deposition of the solids on the flowline wall. This study presents the first measurement of asphaltene interparticle cohesive forces using a micromechanical force (MMF) apparatus, which is similar to that used previously to investigate gas hydrate interparticle cohesion. Asphaltene solids were precipitated from two crude oils, and cohesive force measurements were performed for particle pairs with diameters ranging from 100 to 200 μm. In air, the measured cohesive forces between the asphaltene particles were approximately one-half of those measured between hydrate particles in cyclopentane-saturated nitrogen vapor. Asphaltene cohesive force was measured in liquid cyclopentane, to provide a comparison against cyclopentane hydra...

Micromechanical cohesion force between gas hydrate particles measured under high pressure and low temperature conditions.

To prevent hydrate plugging conditions in the transportation of oil/gas in multiphase flowlines, one of the key processes to control is the agglomeration/deposition of hydrate particles, which are determined by the cohesive/adhesive forces. Previous studies reporting measurements of the cohesive/adhesive force between hydrate particles used cyclopentane hydrate particles in a low-pressure micromechanical force apparatus. In this study, we report the cohesive forces of particles measured in a new high-pressure micromechanical force (MMF) apparatus for ice particles, mixed (methane/ethane, 74.7:25.3) hydrate particles (Structure II), and carbon dioxide hydrate particles (Structure I). The cohesive forces are measured as a function of the contact time, contact force, temperature, and pressure, and determined from pull-off measurements. For the measurements performed of the gas hydrate particles in the gas phase, the determined cohesive force is about 30-35 mN/m, about 8 times higher than the cohesive force of CyC5 hydrates in the liquid CyC5, which is about 4.3 mN/m. We show from our results that the hydrate structure (sI with CO2 hydrates and sII with CH4/C2H6 hydrates) has no influence on the cohesive force. These results are important in the deposition of a gas-dominated system, where the hydrate particles formed in the liquid phase can then stick to the hydrate deposited in the wall exposed to the gas phase.

Micromechanical Systems for the Mechanical Characterization of Muscle Tissue

This contribution describes the femtosecond laser ablation and mechanical characterization of small samples of skeletal muscles. Categories of tissue damage are defined and stiffness values related to the different states of deterioration. The stiffness values are obtained by tactile measurements with micromechanical force sensors and will be applied to the development of force-sensitive micro grippers for the characterization of biological tissues.

Development of a high pressure micromechanical force apparatus

The formation of gas hydrates and subsequent plugging of pipelines are risks that need to be well understood during the production and transportation of oil and gas in subsea flowlines. These flowlines are typically operating at low temperature and high pressure conditions, which are well within the hydrate formation stability region. One of the key processes for hydrate plugs to develop is the agglomeration of hydrates. To obtain a more comprehensive understanding on this problem, we have developed a high-pressure micromechanical force (MMF) apparatus to directly measure cohesive forces between gas hydrate particles. The MMF system is housed in a stainless steel vessel that can withstand pressures of up to 10 MPa, thereby facilitating studies on a broad spectrum of hydrate formers and conditions. The MMF apparatus comprises of two cantilever fibers: one is stationary and another is manipulated via a nano-manipulator. Water droplets (~500 μm in diameter) are placed at the end of the each cantilever fiber so that they can be converted to hydrate. In order to demonstrate the stability of this apparatus, CH4/C2H6 (74.7 mol. %/25.3 mol. %) mixed hydrates were prepared at 2 MPa and -5 °C and annealed at 0 °C for 15 h. Subsequently, the hydrate particle cohesive force was measured at 2 °C. Compared with the cohesive force of cyclopentane hydrates in cyclopentane liquid (~4.3 mN/m), the average cohesive force of gas hydrates was about 10 times higher, ~43 mN/m. Studies using this new high pressure MMF apparatus will be central to better understand the agglomeration of hydrates in multiphase flowlines.

Effect of Kinetic Hydrate Inhibitor Polyvinylcaprolactam on Cyclopentane Hydrate Cohesion Forces and Growth

The effect of Polyvinylcaprolactam (PVCap), a commonly used kinetic hydrate inhibitor (KHI), on the cohesion force between cyclopentane hydrate particles was measured using a micromechanical force apparatus. The presence of PVCap in the aqueous bulk phase reduced the average hydrate cohesive force by 54% (from 1.49 to 0.69 mN/m). However, the cohesion forces did not vary significantly as a function of either the PVCap concentration (0.005–0.5 wt %) or the temperature (from 1.1 to 7.2 °C). When a layer of PVCap solution was applied to the surface of a pure cyclopentane hydrate particle in a bulk liquid cyclopentane phase, the interparticle cohesive force was reduced by 45% (from 4.3 to 2.4 mN/m). Hydrate growth on droplets of PVCap solutions was also studied by contacting a water droplet with a cyclopentane hydrate particle in a bulk cyclopentane phase. In cases where PVCap was absent, complete conversion of the water droplet to hydrate occurred within 30 s. However, when a water droplet of PVCap solution was brought into contact with a hydrate particle, hydrate film growth was significantly slowed, requiring over 2 h for complete conversion.

Investigation of Different Piezoresistive Materials to be Integrated into Micromechanical Force Sensors Based on SU 8 Photoresist

The aim of this scientific work is to present different piezoresistive materials suitable to be integrated into micromechanical force sensors. As material for the mechanical structure of the sensors SU-8 has been chosen because it features favorable characteristics, such as flexible and simple fabrication of micro components through the use of standard UV lithography for forming three dimensional geometries such as cantilevers and membranes. In addition, on the basis of a significantly lower Young’s modulus compared to silicon, great opportunities to improve the force sensitivity of such sensors are offered by SU-8.However, SU-8 photoresist does not have piezoresistive properties, and therefore it has to be combined with an additional, beneficial piezoresistive material. A well-controlled and frequently used material for piezoresistive elements is doped silicon. This paper provides an overview of characteristics such as gauge factor and temperature coefficient of resistance (TCR) for a variety of commonly used piezoresistive materials, namely metals, silicon, conductive composite materials and diamond-like carbon. As a characteristic factor for the estimated sensitivity of the force sensor, the ratio of the gauge factor k to the Young´s modulus E of the structural material is presented for the different material combinations. A classification of conventional silicon based tactile force sensors is made to build a basis for comparison. Furthermore the suitability of different piezoresistive materials for the integration into an SU 8-based sensor is investigated.

Adhesion Force between Cyclopentane Hydrate and Mineral Surfaces

Clathrate hydrate adhesion forces play a critical role in describing aggregation and deposition behavior in conventional energy production and transportation. This manuscript uses a unique micromechanical force apparatus to measure the adhesion force between cyclopentane hydrate and heterogeneous quartz and calcite substrates. The latter substrates represent models for coproduced sand and scale often present during conventional energy production and transportation. Micromechanical adhesion force data indicate that clathrate hydrate adhesive forces are 5-10× larger for calcite and quartz minerals than stainless steel. Adhesive forces further increased by 3-15× when increasing surface contact time from 10 to 30 s. In some cases, liquid water from within the hydrate shell contacted the mineral surface and rapidly converted to clathrate hydrate. Further measurements on mineral surfaces with physical control of surface roughness showed a nonlinear dependence of water wetting angle on surface roughness. Existing adhesive force theory correctly predicted the dependence of clathrate hydrate adhesive force on calcite wettability, but did not accurately capture the dependence on quartz wettability. This comparison suggests that the substrate surface may not be inert, and may contribute positively to the strength of the capillary bridge formed between hydrate particles and solid surfaces.

Model Water-in-Oil Emulsions for Gas Hydrate Studies in Oil Continuous Systems

Stable water-in-oil emulsions with water volume fraction ranging from 10 to 70 vol % have been developed with mineral oil 70T, Span 80, sodium di-2-ethylhexylsulfosuccinate (AOT), and water. The mean size of the water droplets ranges from 2 to 3 μm. Tests conducted show that all emulsions are stable against coalescence for at least 1 week at 2 °C and room temperature. Furthermore, it was observed that the viscosity of the emulsion increases with increasing water volume fraction, with shear thinning behavior observed above certain water volume fraction emulsions (30 vol % at room temperature and 20 vol % at 1 °C). Viscosity tests performed at different times after emulsion preparation confirm that the emulsions are stable for 1 week. Differential scanning calorimetry performed on the emulsions shows that, for low water volume fraction emulsions (<50 vol %), the emulsions are stable upon ice and hydrate formation. Micromechanical force (MMF) measurements show that the presence of the surfactant mixture has ...