Methane hydrate dissociation kinetics can be inhibited in NaCl solutions; however, this effect is reversed by promoting bubble formation that enhances dissociation. The negative and positive effects ...of inorganic salt injection on gas production from hydrate-bearing sediments are still controversial. Here, molecular dynamics simulations were performed to investigate the characteristics of NaCl solution invasion into hydrate-occupied nanopores and the effects on the confined hydrate dissociation kinetics. Two initial configurations comprising liquid and silica pore phases were studied with a low or high NaCl concentration, respectively. The results show that, under the simulation conditions, salt invasion decelerated hydrate dissociation within the silica pore as NaCl invasion into the pore is stepwise. Initially, few ions can diffuse into the pore phase, and gas nanobubbles form on the solid surface mainly via confinement and surface effects, independent of NaCl solution invasion. Subsequently, gradual salt diffusion immersed the residual hydrate in the salt solution and hindered hydrate decomposition until the dissociation finished. More ions could diffuse into the pore phase at the high NaCl concentrations with a low diffusion efficiency, leading to surface nanobubble growth toward the residual hydrate and somewhat accelerated hydrate dissociation. This severely hinders the escape of released methane from the pore. This study yields molecular-level insight into the origin of the negative effect of salt invasion on hydrate dissociation, which should be avoided during gas production from hydrate reservoirs with low permeabilities via salt injection combined with thermal stimulation.
In recent years, polymers used as thickeners in fracturing fluids tend to pursue a higher molecular weight for better thickening performance. However, these polymers experience mechanical degradation ...under high shear conditions. To improve the adaptability of polymer fracturing fluids to mechanical shear, a novel hydrophobically associating polymer (HALMP) was developed by enhancing the hydrophobic association action (to improve viscosity and elasticity) while decreasing the molecular weight (to avoid shear degradation and ensure solubility) and characterized by 1H NMR and infrared tests. The calculated molecular weight of HALMP from intrinsic viscosity is 150 × 104 g/mol, and it was concluded that there is strong hydrophobic association in polymer solution from the microscopic structure and macroscopic properties by pyrene fluorescence probe technique, viscoelasticity, and thixotropy tests. Meanwhile, the critical association concentration and the aggregation pattern of polymer molecules in solution were investigated. The shear recovery tests and scanning electron microscopy revealed that the polymer solution contains a dynamic physical crosslinking network that can be “healed” by the intermolecular hydrophobic association action after being sheared. The results also show that HALMP exhibits excellent thickening performance even at a high shear rate. These findings not only demonstrate the feasibility of polymer fracturing fluids with strong association and low molecular weight but also offer alternative methods to prepare high-functional polymers.
Organophosphorus compounds are well known as oilfield scale inhibitors. Earlier work showed that a series of new and well-known bone-targeting drugs incorporating non-toxic bisphosphonates (BPs) ...(PO3H2–C–PO3H2) gave good scale inhibition performance against calcite scale based on produced water from the Heidrun oilfield, Norwegian Sea, Norway. However, these chemicals showed only moderate calcium compatibility activity. In this project, we attempted to improve the inhibition performance and calcium tolerance of non-toxic BPs by introducing various functional groups (phosphonate (SI-2), sulfonates (SI-3 and SI-5), and carboxylates (SI-4, SI-6, and SI-7)) in the inhibitor structure backbone. All modified alendronic acid derivatives were screened for calcite and gypsum scale inhibition according to the NACE Standard TM0374-2007 protocol. We also report the calcite scale inhibition performance of all synthesized SIs according to the Heidrun oilfield, Norwegian Sea, Norway. In addition, the calcium tolerance and thermal stability activities of all synthesized SIs are reported. The tolerance results showed that all SIs gave better calcium compatibility than BPs reported earlier, with SI-5 giving the best results at high calcium concentrations (10,000 ppm). The corresponding attachment of an iminodi methylene/ethylene sulfonic moiety (i.e., SI-3 and SI-5) showed worse performance against gypsum scaling, whereas the methylenephosphonate derivative (SI-2) and the carboxylated derivatives (SI-4, SI-6, and SI-7) showed improved performance. For calcite scaling, the NACE standard test gave significantly lower inhibition results than the Heidrun-based produced water due to the former having a higher calcium concentration and calcite supersaturation. It was also found that SI-2, SI-5, and SI-7 showed good thermal stability at 130 °C for 1 week.
The delineation of pore size and surface area distribution and methane sorption-diffusion capacity in gas shale reservoirs is crucial for the estimation of storage capacity, anticipating flow ...characteristics, and field development. A systematic approach and guidelines are needed for the analysis of the pore size and surface area distribution of shale formations. The effect of shale sample size on the gas sorption and diffusion properties is not well understood either. The low-pressure nitrogen adsorption technique is a prevalent method for pore characterization of nanoporous shale formations. Although researchers adopted some corrections to the classical method for the analysis of pore size and surface area distribution, there is a significant mismatch between different approaches in depicting fine mesopore size and surface area (2–10 nm). In this study, the classical methods and density functional theory are employed to comparatively analyze the pore characteristics of some shale and clay samples for their applicability, efficacy, and consistency issues. Furthermore, the effect of shale particle size on the methane sorption capacity and diffusion is being investigated. It seems that confinement stress has less of a considerable effect on methane sorption (6% decrease). However, crushing shale rocks into smaller particles can significantly overestimate the methane adsorption capacity. The methane diffusion coefficient also increases with increasing the shale particle size by more than an order of magnitude.
Aviation turbine fuel (jet fuel) must remain fluid enough for use at low temperatures typically experienced during high-altitude flights. The viscosity–temperature relationship of petroleum-derived ...jet fuel is described by the MacCoull correlation in ASTM D341. The maximum kinematic viscosity of jet fuel at −20 °C is regulated by specification, but for long-distance flights, viscosity of <12 mm2 s–1 at −40 °C is important. For synthesized paraffinic kerosene (SPK) to be approved as a synthetic jet fuel, compliance with these viscosity limits is imperative. A petroleum-based kerosene and SPK from wax hydrocracking were distilled into narrow cut (5 °C range) fractions, and for each narrow cut, density, viscosity, and refractive index values were measured over the temperature range from +60 to −60 °C. The viscosity–temperature dependences of the petroleum-derived and synthetic narrow cuts were described with comparable accuracy (relative deviation <5%) by the MacCoull correlation. Calculation of kinematic viscosity at −40 °C by extrapolating data measured at ≥−20 °C underpredicted viscosity for >200 °C boiling kerosene cuts, with a maximum relative deviation of 6.6%. The freezing point is another jet fuel property that is regulated by specification. Good agreement (±1.3 °C) was found between the end of the melting endotherm obtained by differential scanning calorimetry (DSC) and the freezing point determined according to ASTM D2386. Local maxima/minima in the freezing point of distillation cuts with increasing boiling point were observed and could be related to the freezing point characteristics of the n-alkanes.
Shale oil/gas is a type of unconventional energy and an important supplement to the energy structure worldwide. Hydraulic fracturing plays a necessary role in exploiting this kind of resource, and a ...higher salt ion concentration exists in flowback fluid, which is totally different from conventional reservoirs. To understand the special mechanism of high salt ion concentration, the effect of testing conditions on salt ion diffusion behavior by a Mettler SevenExcellence multiparameter conductivity instrument and then salt ions in soaked solution are analyzed. The study samples are selected from lacustrine shale from the Upper Cretaceous Qingshankou Formation. The testing conditions include measuring sites, stirring or not, particle size, sample weight, solution volume, and initial solution concentration. The experiment has perfect repetition as long as 238 days. The conductivity measured at the upside is lower than the one measured at the downside before 10 days and becomes similar after 10 days. Stirring before measurement increases the salt ion diffusion rate obviously before 10 days, which has less influence on the late period. The smaller the particle size is, the higher the conductivity is. The ratio between conductivity and sample weight decreases with sample weight increase. The higher the liquid volume is, the higher the total salt ion in liquid is at last. The initial salt ion concentration has less influence on the salt ion diffusion behavior, which is mainly controlled by its own physical property. Salt ion diffusion needs a long time to approach stability, and the conductivity in some samples is still increasing after 218 days. The main anions in soaked solution are SO4 2–, Cl–, and NO3 –, and the main cations are Na+, Ca2+, Mg2+, K+, Si4+, and Sr2+. Cl– and Sr2+ are mainly from precipitated salt ions in pores, and other salt ions are partially from precipitated salt ions in pores. Our study contributes to understanding the influencing factors for evaluating the salt ion diffusion behavior in the shale reservoir and clarifying the salt ion component in soaked solution, which is conducive to the explanation of flowback fluid with a higher salt ion concentration in clay-rich shale reservoirs. Our research contributes to the selection of high productive shale oil formation.
Microfluidics is relatively a new area in the oil and gas industry and has great potential to be used as an effective tool to address various outstanding research questions where microscale ...investigation is necessary. Low salinity brine flooding has been known to enhance oil recovery in carbonate reservoirs through a wettability alteration mechanism. Wettability alteration is a molecular-scale phenomenon that is often characterized at a mesoscale through contact angle experiments. By using microfluidic chips, the low salinity effects involving solid–fluid interactions could be directly visualized, and the wettability alteration could be verified at microscale. However, to replicate solid–fluid interactions involved in carbonate reservoirs, the internal wetting surfaces must be transformed to carbonate surfaces. In this study, first, wetting surfaces of straight-channel glass microfluidic chips were functionalized using a metal-chelating silane coupling agent, and then, the surfaces were coated with CaCO3 using a layer-by-layer (LbL) deposition process. The calcite-coated straight-channel glass microfluidic chips were then used to investigate the effects of brine salinity and the role of divalent ions in the wettability alteration of oil-wet calcite surfaces at both room temperature and high temperature (70 °C). Naphthenic acid was used as the surface-active component in a model oil to render calcite surfaces oil wet. Six single-electrolyte-based brines were used in this study: high salinity 5 M NaCl, seawater equivalent 0.656 M NaCl, and 4-times diluted seawater-equivalent low salinity brines0.164 M ionic strength NaCl, Na2SO4, MgSO4, and MgCl2. The low salinity brines were found to induce significant wettability alteration on naphthenic-acid-adsorbed calcite surfaces at ambient temperature. Low salinity Na2SO4 resulted in the highest wettability alteration followed by low salinity NaCl solution. Insignificant wettability alteration was observed in 0.656 M NaCl compared to 0.164 M NaCl where the wettability alteration was significant, suggesting the extent of wettability alteration increases with reduction in brine salinity. Magnesium ions were found to be unfavorable for wettability alteration in the presence or absence of sulfate ions. Exposure to higher temperature resulted in no or insignificant further wettability alteration in most of the brines.
Cetacean Paleobiology Marx, Felix G; Lambert, Olivier; Uhen, Mark D
2016, 2016-03-29
eBook
Cetaceans (whales, dolphins, and porpoises) have fascinated and bewildered humans throughout history. Their mammalian affinities have been long recognized, but exactly which group of terrestrial ...mammals they descend from has, until recently, remained in the dark. Recent decades have produced a flurry of new fossil cetaceans, extending their fossil history to over 50 million years ago. Along with new insights from genetics and developmental studies, these discoveries have helped to clarify the place of cetaceans among mammals, and enriched our understanding of their unique adaptations for feeding, locomotion and sensory systems. Their continuously improving fossil record and successive transformation into highly specialized marine mammals have made cetaceans a textbook case of evolution - as iconic in its own way as the origin of birds from dinosaurs. This book aims to summarize our current understanding of cetacean evolution for the serious student and interested amateur using photographs, drawings, charts and illustrations.
Determining water occurrence in pore-fracture systems under specific water saturation is of great significance to reveal the correlation between the water content and porosity/permeability of coal ...reservoirs. In this work, simulation experiments of water intrusion and drainage are used to study the micro-occurrence and migration of water using NMR T 2 and T 1–T 2 techniques and discuss the influence of pore-fracture system structure parameters on water micro-occurrence. Meanwhile, water distribution heterogeneity in the pore-fracture system is clarified by single- and multifractal theories. The results show that (1) the vacuum saturation method without pressure is unsuitable for high-rank coal samples with micropore development, and water saturation variation leads to a change in significant permeability when water saturation is greater than the critical value, which is related to the coal rank and degree of fracture development; (2) the single-fractal theory can characterize the heterogeneity of water and pore size distribution under static conditions; however, multifractal analyses have a stronger applicability in characterizing water distribution heterogeneity under dynamic conditions; and (3) multifractal parameters have a good correlation with coal sample characteristics such as the water volume in pores and fractures. In the process of centrifugation, both D –10–D 0 and D –10–D 10 parameters from fractal analyses decrease linearly with a decrease in water content in coal samples, indicating that water distribution heterogeneity in pore-fracture systems decreases with an increase in centrifugal force; and (4) T 2 and two-dimensional spectra in the same coal sample should be comprehensively analyzed as they can quantitatively identify the amount of water migration at different saturation stages.
The effects of air pollution control devices (APCDs) such as selective catalytic reduction systems, electrostatic precipitators (ESPs), seawater desulfurization (SWFGD) units, and wet ESPs (WESP) on ...the ultralow emissions of trace elements (TEs) in a 300 MW pulverized coal boiler system are studied to reveal the removal of TEs (As, Se, and Pb) in these facilities. The results show that the average synergistic removal efficiencies of As, Se, and Pb in the studied power plant are 97.26, 94.07, and 95.49%, respectively. The emission concentration of As, Se, and Pb did not exceed 0.17, 0.67, and 4.23 μg/m3, respectively. ESPs can capture a great part of As and Pb; most of the Se is removed in the SWFGD system and WESP. The flue gas temperature decreasing in the air preheater (APH) and flue gas cooling system facilitates particulate TE removal in the ESP. Seawater in the SWFGD system promotes the dissolution and removal of unfilterable TEs, making the SWFGD system more efficient than conventional WFGDs under some working conditions. The influence of the boiler load and sulfur content of coals on the migration and transformation characteristics of TEs has also been systematically studied. Burning coal with a higher sulfur content can improve the synergistic removal of Pb, and working under a low boiler load is beneficial to the synergistic removal of As, Se, and Pb by APCDs of power plants. Hopefully, this study can provide a reference for the removal of TEs under various operating conditions in power plants with different APCDs.
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