Effect of oil composition on fluid substitution in heavy oil reservoirs

Unlike light oils, heavy oils do not have a well‐established scheme for modelling elastic moduli from dynamic reservoir properties. One of the main challenges in the fluid substitution of heavy oils is their viscoelastic nature, which is controlled by temperature, pressure, and fluid composition. Here, we develop a framework for fluid substitution modelling that is reliable yet practical for a wide range of cold and thermal recovery scenarios in producing heavy oils and that takes into account the reservoir fluid composition, grounded on the effective‐medium theories for estimating elastic moduli of an oil–rock system. We investigate the effect of fluid composition variations on oil–rock elastic moduli with temperature changes. The fluid compositional behaviour is determined by flash calculations. Elastic moduli are then determined using the double‐porosity coherent potential approximation method and the calculated viscosity based on the fluid composition. An increase in temperature imposes two opposing mechanisms on the viscosity behaviour of a heavy‐oil sample: gas liberation, which tends to increase the viscosity, and melting, which decreases the viscosity. We demonstrate that melting dominates gas liberation, and as a result, the viscosity and, consequently, the shear modulus of the heavy oils always decrease with increasing temperature. Furthermore, it turns out that one can disregard the effects of gas in the solution when modelling the elastic moduli of heavy oils. Here, we compare oil–rock elastic moduli when the rock is saturated with fluids that have different viscosity levels. The objective is to characterize a unique relation between the temperature, the frequency, and the elastic moduli of an oil–rock system. We have proposed an approach that takes advantage of this relation to find the temperature and, consequently, the viscosity in different regions of the reservoir.     

Hydrocarbon composition and distribution in a coastal region under influence of oil production in northeast Brazil

Waters and sediments from the Potiguar Basin (NE Brazilian coast) were investigated for the presence and nature of polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons. The region receives treated produced waters through a submarine outfall system serving the industrial district. The total dispersed/dissolved concentrations in the water column ranged from 10-50 ng L⁻¹ for ∑16PAH and 5-10 μg L⁻¹ for total aliphatic hydrocarbons. In the sediments, hydrocarbon concentrations were low (0.5-10 ng g⁻¹for ∑16PAH and 0.01-5.0 μg g⁻¹ for total aliphatic hydrocarbons) and were consistent with the low organic carbon content of the local sandy sediments. These data indicate little and/or absence of anthropogenic influence on hydrocarbon distribution in water and sediment. Therefore, the measured values may be taken as background values for the region and can be used as future reference following new developments of the petroleum industry in the Potiguar Basin.     

Compound-specific stable carbon isotopic composition of petroleum hydrocarbons as a tool for tracing the source of oil spills

With the increasing demand for and consumption of crude oils, oil spill accidents happen frequently during the transportation of crude oils and oil products, and the environmental hazard they pose has become increasingly serious in China. The exact identification of the source of spilled oil can act as forensic evidence in the investigation and handling of oil spill accidents. In this study, a weathering simulation experiment demonstrates that the mass loss of crude oils caused by short-term weathering mainly occurs within the first 24h after a spill, and is dominated by the depletion of low-molecular weight hydrocarbons (相似文献   

Ion--neutral friction as a model for magnetic relaxation

It is generally admitted that a plasma in the absence of forcing will relax to a minimum energy state compatible with appropriate constraints. Usually this is a force-free state, which, in two dimensions, implies a potential magnetic field except by the possible presence of current sheets. The precise mechanism of this relaxation, and in particular the plasma velocity, are generally ignored. There exists, however, a physically well-defined process that should produce magnetic relaxation: ion--neutral (or ambipolar) friction. While there is no guarantee of the existence of a limit of this process when t?→?∞, there exists a family of sequential limits for whom the Lorentz force tends to zero. To analyze the configuration of these limit states, we study the evolution of several moments of the magnetic energy. We prove that for as long as the enstrophy remains bounded, the current density energy also remains bounded in two dimensions: this excludes all classical configurations of current sheets across which the magnetic field reverses direction. Hence, these sheets cannot be the limit of ion--neutral diffusion unless the flow becomes increasingly irregular over time.     

The micromechanics of friction in a granular layer

A grain bridge model is used to provide a physical interpretation of the rate- and state-dependent friction parameters for the simple shear of a granular layer. This model differs from the simpler asperity model in that it recognizes the difference between the fracture of a grain and the fracture of an adhesion between grains, and it explicitly accounts for dilation in the granular layer. The model provides an explanation for the observed differences in the friction of granular layers deformed between rough surfaces and those deformed between smooth surfaces and for the evolution of the friction parameters with displacement. The observed evolution from velocity strengthening to velocity weakening with displacement is interpreted as being due to the change in the micromechanics of strain accommodation from grain crushing to slip between adjacent grains; this change is associated with the observed evolution of a fractal grain structure.     

Crude-oil hydrocarbon composition characteristics and oil viscosity prediction in the northern Songliao Basin

Crude oil hydrocarbon composition characteristics and oil viscosity prediction are important bases in petroleum exploration.A total of 54 oil/heavy-oil samples and 17 oil sands were analyzed and quantified using both comprehensive 2D gas chromatography(GC×GC)and comprehensive 2D gas chromatography/time-of-flight mass spectrometry(GC×GC/TOFMS).The results show that crude oil in the West slope is mainly heavy oil and its hydrocarbon composition is characterized overall by paraffinsmono-aromaticsnaphthenesnon-hydrocarbonsdi-aromaticstri-aromaticstetra-aromatics.Aromatics are most abundant and non-hydrocarbons are least abundant,whilst content differences among paraffins,naphthenes,aromatics,and non-hydrocarbons are less than 15%.There are two types of heavy oil,secondary type and mixing type.Biodegradation is the main formation mechanism of heavy oil.Biodegradation levels cover light biodegradation,moderate biodegradation,and severe biodegradation.With increasing biodegradation,paraffin content decreases while contents of aromatics and nonhydrocarbons increase.In contrast,naphthene content increases first and then decreases with increasing biodegradation.In severe biodegradation stage,naphthenes decrease more quickly than aromatics and non-hydrocarbons.This provides a new method for studying oil/heavy-oil biodegradation mechanism and biodegradation resistance of different hydrocarbons at different biodegradation stages.In the Longhupao-Daan terrace and Qijia-Gulong depression,most crude oil is conventional oil.Its composition is dominated by paraffins with the lowest content of aromatics.In some casual oil wells from the Longhupao-Daan terrace,crude oil from Saertu oil reservoirs is moderately biodegraded whereas crude oil from Putaohua oil reservoir is lightly biodegraded.Chemical parameters using saturate hydrocarbons and aromatics are usually not suitable for determining organic type and thermal maturity of biodegraded oil,especially of moderately or severely biodegraded oil,whilst Ts/(Ts+Tm)ratio can be used to determine thermal maturity of both conventional crude oil and heavy oil.     

Nonuniform friction as a physical basis for earthquake mechanics

A review of simple models and observations suggests that the main first-order features of active faulting-mechanical instability, the frequency-magnitude relations, seismic and aseismie slip, seismic radiation, incoherency and rupture stoppage — may be explained by a single characteristic of crustal faults: the spatial variation of the effective frictional stress, which resists slippage on faults. Faultoffset data suggest that rupture propagation ceases in regions of high resistance which act, as barriers. In these regions slippage is associated with negative stress drop. The spacing and the amplitudeA() of the barriers, as inferred from the frequency-magnitude and moment relation for earthquakes, obeys a simple statistical relationA()^p. On the scale of particle motion, this variability of frictional stress provides a mechanical instability which may be associated with the concept of dynamic friction. Invariably, the rapid particle motion in the model is always preceded by accelerated creep. The particle acceleration is highly irregular, giving rise to an almost random acceleration record on the fault. The particle displacement is relatively smooth, giving rise to simple displacement time function in the far field. Rupture propagation time is approximately proportional to the gradient of frictional stress along the fault. Consequently sharp changes of this stress may cause multiple events and other long period irregularities in the fault motion.The power density spectrum associated with the frictional stress implies that stress may be related to a Poisson distribution of lengths. The autocorrelation of such type of distribution yields a correlation lengthk _L ^–1 , similar perhaps toHaskell's (1964) andAki's (1967) correlation lengths inferred from spectral analysis of seismic waves. The partial incoherency of faulting implies that preseismic deformation may be significantly incoherent, consequently the prediction of small moderate earthquakes may be subject to inherent uncertainties. We conclude that frictional stress heterogeneities may be necessary and sufficient to explain active faulting associated with small and moderate earthquakes.     

Seismicity simulation with a rate- and state-dependent friction law

The dynamic motions and stabilities of a single-degree-of-freedom elastic system controlled by different friction laws are compared. The system consists of a sliding block connected to an elastic spring, driven at a constant velocity. The friction laws are a laboratory-inferred friction law called the rate-and-state-dependent friction law, proposed by Dieterich and Ruina, and a simple friction law described by dynamic and static frictions. We further extend the solution to a one-dimensional mass-spring model which is an analog of a fault controlled by the rate-and-state-dependent friction law. This model predicts non uniform slip and stress drop along the rupture length of a heterogeneous fault. This result is very different from some earlier modelings based on the simple friction law and a slip weakening friction law. In those earlier modelings the stress and slip functions become smoother with time along the length of the fault rupture, owing to the interactions between fault segments during slip. Because of this smoothing process the number of small events will decrease with time, and the universilly observed stationary magnitude-frequency relation cannot be explained. The interaction between a fault segment and its neighboring segments can be measured when the post-slip stress on this segment is compared with the stress on an identical segment (represented by a block in this modeling) without neighboring segments. If the post-slip stress of the former is much higher than that of the latter, strong interaction exists; if the two are close, only weak interaction exists. The interaction is determined by the relative motion between fault segments and the time duration of interaction. Our new modeling with the rate-and-state-dependent friction law appears to show no such smoothing effect and provides a physical mechanism for the roughening process in the difference between the fault strength and stress that is necessary to explain the observed stationary magnitude-frequency relation. The noninstantaneous healing predicted by the rate-and-state-dependent friction law may be repsonsible for the recurring nonuniform slip and stress drop, and may be explained by the reduction of interaction among fault segments due to the low frictional strength during the fault stopping. The very low friction during slip stopping allows much longer times than does the higher friction due to instantaneous healing for the fault segments to adjust their motions from an upper-limit slip velocity to almost rest. According to newton's second law, a process with fixed masses and constant velocity changes involves low forces and weak interactions if it is accomplished in a long time period, and vice versa. Our modeling also indicates that the existence of strong patches with higher effective stress on a fault is needed for the occurrence of major events. The creeping section of a fault, such as the one along the San Andreas fault in central California, on the other hand, can be simulated with the rate-and-state-dependent friction law by certain model parameters, which, however, must not include strong patches. In this case small earthquakes and aseismic creep relieve the accumulating strain without any large events.     

Extreme behavior in a triple friction pendulum isolated frame

While isolation can provide significantly enhanced performance compared to fixed‐base counter parts in design level or even maximum considered level earthquakes, there is still uncertainty over the performance of isolation systems in extreme events. Researchers have looked at component level stability of rubber bearings and on the effect of moat impact on behavior of structures isolated on general bilinear isolators. However, testing of triple friction pendulum (TFP) sliding bearings has not been done dynamically or incorporated into a building system. Here, one‐third scale laboratory tests were conducted to on a 2‐story 2‐bay TFP‐isolated structure. Input motions were increasingly scaled until failure occurred at the isolation level. As the superstructure was designed with a yield force equivalent to the force of the bearing just at their ultimate displacement capacity, there was minimal yielding. A numerical model is presented to simulate the isolated building up to and including bearing failure. Forces transferred to the superstructure in extreme motions are examined using both experimental and numerical data. Additionally, the effect of the hardening stage of the TFP bearing is evaluated using the numerical model, finding slight benefits.     

Seismicity simulation with a mass-spring model and a displacement hardening-softening friction law

Dieterich simulated aftershocks numerically, using a one-dimensional mass-spring model with a time-dependent friction law. But an important precursory phenomenon called quiescence cannot be produced by this model unless, as Mikumo and Miyatake showed with a three-dimensional continuum model, a somewhat arbitrary bimodal distribution of frictional strength is assumed. Here we used the friction law proposed by Stuart, which is a displacement hardening-softening model, and simulated the quiescence. By varying the parameters of the friction law in our mass-spring model, we found a variety of seismicity patterns. When we choose extremely large critical displacement we get a recurrent sequence of creep followed by mainshock without small earthquakes. But when we choose a critical displacement in the same order of magnitude as the slip-weakening critical displacement estimated by Papageorgiou and Aki from strong motion data, we get a normal seismicity pattern, including quiescence before large events. This simple model points to a promising approach for the interpretation of the rupture process during an earthquake by the same physical model.     

The bacterial community composition of an active oil field in the northwestern Gulf of Mexico

The bacterial composition of the water column around two oil production platforms and a control site was examined. Samples were collected during three seasons of a 12-month sampling period three water depths were sampled at all stations occupied.No major differences were discovered in taxonomic or physiological makeup of bacterial populations of the oil field and control site. The genus Pseudomonas predominated at the oil field stations and the control. Bacterial numbers were lower for oil field stations than the control and generally decreased with depth. Microbial biomass estimates were consistently higher at the control site. Oil degrading and sulphur oxidizing bacteria were more numerous within the oil field, and their numbers decreased with distance from the platforms. Buccaneer crude oil did not adversely affect growth or attachment ability of oil field isolates.     

The effect of Prestige oil ingestion on the growth and chemical composition of turbot otoliths

Juvenile turbot (Scophthalmus maximus) were kept in captivity and were fed a prepared food contaminated with five different concentrations of seawater-accommodated fuel oil from 2.4+/-0.35 to 48.2+/-2.2 mg g(-1) food, with a control group receiving uncontaminated food. The growth and survival of individually tagged fish (N=202) were measured after a six-week treatment period. The otolith growth rate was measured and otolith composition was determined before and after the treatments using LA-ICPMS. Fish and otolith growth were negatively affected by the fuel oil treatment, and the response decreased with the level of contamination. Otolith growth and element incorporation peaked at mid level exposures and decreased at the highest level. The otolith elemental composition reflected the presence of some elements in the Prestige fuel that may have been incorporated through the diet into the otolith.     

Chaotic seismic faulting with a mass-spring model and velocity-weakening friction

We present a systematic analysis of the dynamical behavior introduced by fault zone heterogeneities, using a simple mass-spring model with velocity-weakening friction. The model consists of two sliding blocks coupled to each other and to a constant velocity driver by clastic springs. The state of this system can be characterized by the positions of the two blocks relative to the driver. Symmetry stabilizes the system and generates only cyclic behavior. For an asymmetric system where the frictional forces for the two blocks are not equal, the solutions exhibit chaotic behavior. The transition from stable cyclic behavior to chaos is characterized by the period-doubling route to chaos. Lyapunov exponents are computed to quantify the deterministic chaos and to locate the onset of the chaotic evolution in parameter space. In many examples of deterministic chaos, chaotic behavior of a low-order system implies chaos in similar higher order systems. Thus, our results provide substantial evidence that crustal deformation is an example of deterministic chaos.     

一种SMA复合摩擦阻尼器的设计与性能研究

利用形状记忆合金(SMA)的超弹性特性,将SMA丝与摩擦阻尼器复合,提出了一种SMA复合摩擦阻尼器,给出了SMA复合摩擦阻尼器的工作机理和设计方法,建立了其理论模型,确定了SMA复合摩擦阻尼器的力-位移滞回曲线,并对一SMA复合摩擦阻尼器控震单自由度体系在地震作用下的动力响应进行了数值模拟。结果表明,提出的SMA复合摩擦阻尼器具有优良的耗能减振性能。     

新型自复位变摩擦阻尼器试验研究

目前阻尼器运用广泛,但传统摩擦阻尼器无法适应不同的振动强度,且在地震作用后损坏严重,没有自复位功能。文章利用形状记忆合金的超弹性,提出一种新型的自复位变摩擦阻尼器,介绍了阻尼器的构造、基本工作原理并推导了其力学模型,之后对阻尼器进行了力学试验。得到如下结论：该阻尼器不仅能在不同等级地震作用下满足耗能要求,还具有良好的自复位能力;力学试验得到的滞回曲线与理论推导的力学模型吻合较好,印证了力学模型的正确性;该阻尼器耗能能力随着合金丝直径、螺栓预紧力和坡面坡度的增大而增强;残余位移随着合金丝直径和坡面坡度增大而减小、随着预紧力增大而增大。     

Tidal friction in a sea with two equal semidiurnal tidal constituents

The effect of quadratic friction on tidal currents consisting of equal M₂ and S₂ constituents is considered. It is shown by two separate arguments—one based on an energy balance, the other on harmonic analysis of the frictional force—that, for rectilinear and parallel currents, the drag coefficient applicable to either constituent considered in isolation should be 1.70 times greater than that applied to the two constituents propagating together. The results of a numerical model of the tides in Gulf St Vincent, Australia (where equal M₂ and S₂ tides occur) are consistent with this prediction. A general result of this work is that the drag coefficients predicted by harmonic analysis of the friction force give the correct rate of energy dissipation for any number of tidal constituents, equal or not.     

Seismic analysis of a LNG storage tank isolated by a multiple friction pendulum system

The seismic response of an isolated vertical, cylindrical, extra-large liquefi ed natural gas (LNG) tank by a multiple friction pendulum system (MFPS) is analyzed. Most of the extra-large LNG tanks have a fundamental frequency which involves a range of resonance of most earthquake ground motions. It is an effective way to decrease the response of an isolation system used for extra-large LNG storage tanks under a strong earthquake. However, it is diff icult to implement in practice with common isolation bearings due to issues such as low temperature, soft site and other severe environment factors. The extra-large LNG tank isolated by a MFPS is presented in this study to address these problems. A MFPS is appropriate for large displacements induced by earthquakes with long predominant periods. A simplifi ed fi nite element model by Malhotra and Dunkerley is used to determine the usefulness of the isolation system. Data reported and statistically sorted include pile shear, wave height, impulsive acceleration, convective acceleration and outer tank acceleration. The results show that the isolation system has excellent adaptability for different liquid levels and is very effective in controlling the seismic response of extra-large LNG tanks.     

Chemical evolution of Macondo crude oil during laboratory degradation as characterized by fluorescence EEMs and hydrocarbon composition

The fluorescence EEM technique, PARAFAC modeling, and hydrocarbon composition were used to characterize oil components and to examine the chemical evolution and degradation pathways of Macondo crude oil under controlled laboratory conditions. Three major fluorescent oil components were identified, with Ex/Em maxima at 226/328, 262/315, and 244/366 nm, respectively. An average degradation half-life of ～20 d was determined for the oil components based on fluorescence EEM and hydrocarbon composition measurements, showing a dynamic chemical evolution and transformation of the oil during degradation. Dispersants appeared to change the chemical characteristics of oil, to shift the fluorescence EEM spectra, and to enhance the degradation of low-molecular-weight hydrocarbons. Photochemical degradation played a dominant role in the transformation of oil components, likely an effective degradation pathway of oil in the water column. Results from laboratory experiments should facilitate the interpretation of field-data and provide insights for understanding the fate and transport of oil components in the Gulf of Mexico.