Density Window Research Articles

Research and Application of Cement Plugging Techniques in Evaporite Bed of Piedmont Tectonic Belt of the Tarim Basin

Situated on the piedmont tectonic belt of Tarim Basin, well KS-37 encountered large-section evaporite bed at the depth from 5100m to 5400m. Complicated geological conditions and narrow pressure safe density window prevent the cementing plug project to some degree. 2.26g/cm3 forerunner slurry, 2.26g/cm3 saturated saltwater spacer fluid aggravated by micro-manganese and 2.30 g/cm3 intumescence cement slurry, combined with corresponding technical measures have been utilized in the evaporite bed. As a result, cement plug operation has been accomplished successfully so as to meet the engineering requirements of side tracking. It is indicated based on field application that great progress has been made in the adoption of cement slurry of high density as well as corresponding technical measures, which can meet the requirements of plugging cement in evaporite bed in the condition of narrow pressure safe window.

Electron density window for best frequency performance, lowest phase noise and slowest degradation of GaN heterostructure field-effect transistors

The problems in the realm of nitride heterostructure field-effect transistors (HFETs) are discussed in terms of a novel fluctuation–dissipation-based approach impelled by a recent demonstration of strong correlation of hot-electron fluctuations with frequency performance and degradation of the devices. The correlation has its genesis in the dissipation of the LO-mode heat accumulated by the non-equilibrium longitudinal optical phonons (hot phonons) confined in the channel that hosts the high-density hot-electron gas subjected to a high electric field. The LO-mode heat causes additional scattering of hot electrons and facilitates defect formation in a different manner than the conventional heat contained mainly in the acoustic phonon mode. We treat the heat dissipation problem in terms of the hot-phonon lifetime responsible for the conversion of the non-migrant hot phonons into migrant acoustic modes and other vibrations. The lifetime is measured over a wide range of electron density and supplied electric power. The optimal conditions for the dissipation of the LO-mode heat are associated with the plasmon-assisted disintegration of hot phonons. Signatures of plasmons are experimentally resolved in fluctuations, dissipation, hot-electron transport, transistor frequency performance, transistor phase noise and transistor reliability. In particular, a slower degradation and a faster operation of GaN-based HFETs take place inside the electron density window where the resonant plasmon-assisted ultrafast dissipation of the LO-mode heat comes into play. A novel heterostructure design for the possible improvement of HFET performance is proposed, implemented and tested.

Self-energy of strongly interacting fermions in medium: A holographic approach

We consider the self-energy of strongly interacting fermions in the medium using gauge/gravity duality of D4/D8 system. We study the mass generation of the thermal and/or dense medium and the collective excitation called plasmino, by considering the spectral function of fermion and its dispersion relation. Our results are very different from those of the hard thermal loop method: for zero density, there is no thermal mass or plasmino in any phase. Plasmino in the deconfined phase is not allowed in D4/D8 setup. In the confined phase, there is a plasmino mode only for a window of density.

Study and Application of New Technology to Increase Drilling Speed of Ultra-Deep Well in Yuanba Area

The geologic condition in Yuanba Area is quite complex.The drilling problems of formation leakage, pressure differential sticking, narrow density windows and other issues are more and more prominent. Drilling efficiency is low with long drilling cycle because of abnormal complex engineering geological characteristics such as thick continental formation, interbeded sand shale, poor drillability, ultra-high pressure in J 1 z and T 3 x formation, narrow pressure window. 12 completed wells in Yuanba area are analyzed, the conclusion can be draw that improving drilling efficiency in Yuanba region is quite potential if complexity underlying can be decreased and ROP can be improved. In view of this, the matching drilling technologies and tools are introduced and applied, the result show that optimization technology of casing program, bit optimization, gas drilling technology, compound drilling technology and corresponding new tools has made great success in Yuanba area, the average ROP was increased by 20.25%, drilling period was shortened by 18.33%, and the average complex accident handling time was reduced by 25.40%, which provides a good reference for ultra-deep well drilling. Key words : Ultra-deep well; Gas drilling; Bit optimization; Compound drilling; Drilling ROP

Thick Single Grain Silicon Formation with Microsecond Green Laser Crystallization

625 nm thick a-Si layer was crystallized by using microsecond pulsed green laser with wavelength of 515 nm. At least 8 μm size grains were formed using location controlled single grain technique at room temperature. Energy density window for crystallization and ablation were compared for pulse durations of 300 ns, 1000 ns and 1200 ns.

Physical Characterization of Sb2O3-M2O-MoO3(M~= Li,~K) New Glasses

New heavy metal oxide glasses involving Sb2O3 have been investigated. By using classical routes (melting-casting), glasses synthesized in silica crucibles were obtained in the combination of ternary systems Sb2O3-M2CO3-MoO3 (M = Li and K). Characteristic temperatures such as glass transition Tg, and onset of the crystallization Tx, have been measured using di erential scanning calorimeter. Ultrasonic velocities were measured by using pulse echo method to determine the elastics parameters, such as elastic modules (E, G, K, L). Other physical properties were measured, such as density and optical transmission window in far infrared spectra using KBr pellets. In uence of composition on these physico-chemical properties is discussed and correlated to the glass structure.

Ionic liquids based on bis(2,2,2-trifluoroethoxysulfonyl)imide with various oniums

New class of hydrophobic ionic liquids based on bis(2,2,2-trifluoroethoxysulfonyl)imide ([(CF3CH2OSO2)2N]−, TFESI−) anion with various oniums, including N,N-dialkylimidazolium, tetraalkyl (ether-containing alkyl) ammonium, N-alkyl-N-methyl-pyrrolidinium, and -piperidinium, are prepared and characterized. Their physicochemical and electrochemical properties, including phase transitions, thermal stability, viscosity, density, ionic conductivity and electrochemical windows, have been determined. The influences of the structural variations in both the cation and anion on the above properties are extensively discussed. The key features of these new TFESI−-based ionic liquids are their low melting points (ranging from 9 to 44°C) and/or low glass transition (between −74 and −61°C), relatively low viscosities (44–426cP at 25°C), good thermal stability (Td>270°C), and wide electrochemical windows (ranging from 5.7 to 6.4V).

Study on Borehole Stability of Unconsolidated Sandstone in Depleted Reservior

Reservoir pressure will decline generally along with production in the oil and gas development process. There are some problems such as borehole collapse or reduced diameter and lost circulation in drilling of initial production stage in unconsolidated sandstone. As the formation pressure declines the stress around borehole changes, and then collapse pressure and fracture pressure are affected. Especially in directional wells, variation of wellbore stability is more complex with different borehole deviation and azimuth. The calculation models of collapse and fracture pressure in depleted reservoirs were established, and relevant data in unconsolidated sand reservoir of an oilfield in Bohai Sea was used to calculate collapse pressure and fracture pressure of directional wells in the condition of pressure depletion before and after. The results showed that collapse and fracture pressure decreased as formation pressure depletion, and safe drilling fluid density window was wider when drilled to the direction of minimum horizontal principle stress. The calculation results can be reference to drilling design of adjustment wells in unconsolidated sandstones.

Grafting Bimodal Polymer Brushes on Nanoparticles Using Controlled Radical Polymerization

RAFT (reversible addition–fragmentation chain transfer) polymerization has been widely used to synthesize different polymer architectures such as polymer brushes on nanoparticles for incorporation into polymer nanocomposites. It is believed that these polymer brushes, with the same chemistry as the matrix polymer, can be employed to improve filler dispersion by compatibilizing unfavorable enthalpic interactions between the inorganic nanoparticles and their organic host matrices. However, monomodal brush graft nanoparticles are found to aggregate into a range of isotropic and anisotropic morphologies, formed due to a delicate balance between enthalpic and entropic interfacial interactions. This coupling of enthalpy and entropy leaves only a small window of graft densities and molecular weights to obtain randomly dispersed filler morphologies. These issues can be countered by using a bimodal polymer brush that contains a small number of long homopolymer chains that can entangle, and a high density of short brushes that screens the particle/particle attraction, thereby aiding in decoupling the interfacial enthalpic and entropic interactions. In the present work, we demonstrate a robust step-by-step technique using RAFT polymerization to synthesize these bidisperse/bimodal polymer brush-anchored nanoparticles. A layer of dense brush of the first population was initially prepared using surface-initiated RAFT polymerization from colloidal silica nanoparticles. After cleavage of the chain transfer agent from the first population of chain ends, a second RAFT agent was attached onto the silica nanoparticles and then a monomer, which may be the same or different from the first brush, was polymerized. This versatile and widely applicable route enables us to independently control the molecular variables of the attached chains, such as composition, molecular weights and graft densities of the individual populations. The bimodal brush-grafted colloidal silica nanoparticles show superior dispersion and interaction with a homopolymer matrix when compared to monomodal brush-grafted particles.

L–H transition in the presence of magnetic perturbations in ASDEX Upgrade

The L–H transition and the H-mode behaviour in the presence of non-axisymmetric n = 2 magnetic perturbations have been investigated. At low density no effect on the L–H transition is observed. Within a rather narrow density window around 50% of the Greenwald density limit, a transition to H-mode with small ELMs only and good confinement can be achieved. However, a strong density dependence of the L–H threshold power in the presence of magnetic perturbations forces the plasmas to remain in L-mode when the density is above 60% of the Greenwald value. The H-mode confinement time is not affected by the presence of the magnetic perturbations. All of these H-modes, with and without ELM mitigation, exhibit a common confinement degradation with increasing recycling.

A fluid-solid-chemistry coupling model for shale wellbore stability

Abstract A fluid-solid-chemistry coupling model is built considering fluid flow and ion transmission induced by shale-drilling fluid system electrochemical potential osmosis, nonlinearity of flow and solute diffusion in shale-drilling fluid system, and solid deformation resulted from fluid flow and ion transmission. The model is used to compute the time-varying pore pressure, stress and damage index in formations around the wellbore of a well. The result shows that the pore pressure and stress are lower without consideration of the diffusion potential induced by ion selective character of shale membrane. The linear model overestimates the pore pressure and stress fields around the sidewall. The damage index reveals that collapse first occurs in formations near the wellbore, the caving pressure increases and changes obviously with time, the fracture pressure reduces but doesn't change significantly with time, and the drilling fluid density window narrows down with time.

An Experimental Study on Creep Characteristics of Salt Rock and Gypsum-salt Rock in Puguang Gas Field

Through the determination of mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field and the creep experiments on these rocks, the authors analyze the impacts of mineralogical compositions, deviatoric stress, temperature, and confining pressure on creep behavior and proposes the constitutive equation of steady-state creep rate by combining with the creep curve and rock parameters obtained by the experiments. The experiment results indicate that the main mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field are sodium chloride and calcium sulfate, where the content of sodium chloride can be up to more than 93%; the inherent mineralogical compositions are the internal factors that impact the creep characteristics of rock, along with the content of sodium chloride increasing, the rates of transient creep and steady-state creep increase accordingly; and as the deviatoric stress and temperature increase, the steady-state creep rate increases too. However, the impact of confining pressure is very small. The authors obtain the parameters of Heard's creep constitutive equation by fitting test data, working out the steady-state creep rates of salt rock and gypsum-salt rock under different deviatoric stresses and temperatures, which provides the theoretical basis of the calculation of safe mud density window and the analysis of abnormal casing deformation for the formations of salt rock and gypsum-salt rock in Puguang gas field.

Enhanced memory window of Au/BaTiO3/SrTiO3/Si(001) MFIS structure with high c-axis orientation for non-volatile memory applications

Metal–ferroelectric–insulator–semiconductor (MFIS) structures with BaTiO3 (BTO) as a ferroelectric film and SrTiO3 (STO) as an insulating buffer layer were fabricated on p-type Si(001) substrates using an ion beam sputter deposition technique. The effect of out-of-plane orientation on the electrical properties of the MFIS structures, including leakage current density and memory window behavior, were studied using the growth of the BTO ferroelectric film on Si substrate buffered by highly c-axis-oriented and random-oriented STO buffer layers. The experimental results show that the out-of-plane orientations of the BTO films were almost identical to those of the STO buffer layers. The MFIS structure with a high c-axis orientation exhibited a maximum clockwise capacitance-voltage memory window of 1.17 V with a low leakage current of 1.05×10−7 A/cm2 at an applied voltage of 4 V, which is a significant improvement compared to the MFIS structure with a random orientation. The difference in the electrical properties of the MFIS structures with both types of orientation is discussed in detail. The results obtained from this study indicate that the Au/BTO/STO/p-Si MFIS structure with high c-axis orientation has good potential for use in non-volatile memory applications.

Rock Mechanics Parameters Calculation of the Fractured Rock Based on the Effective Media Theory with Well Logging

Fractured rocks are the main oil and gas exploration objects offshore in China in recent years, which include the fractured sandstone, carbonate, volcanic rock, coal methane bed, shale gas and so on. The accurate calculation of the rock mechanics parameters (elastic modulus and Poisson’s ratio) play remarkable role in petroleum engineering operations, such as borehole stability, mud density window determination, perforation, EOR, in-situ stress predication and so on. Now the applications show that the in-situ stress estimation based on the rock parameters obtained by acoustic logging is much different from the downhole measurement with wireline formation tester. The pore space of the fractured rock contains fracture and cave and it is different from sandstone. In the paper a novel method based on the effective media theory with well logging for the rock mechanics parameters calculation of the fractured rock is introduced, and some problems and potential application are also discussed.

Wigner crystal in snaked nanochannels: Outlook

We study properties of Wigner crystal in snaked nanochannels and show that they are characterized by a conducting sliding phase at low charge densities and an insulating pinned phase emerging above a certain critical charge density. We trace parallels between this model problem and the Little suggestion for electron transport in organic molecules. We also show that in the presence of periodic potential inside the snaked channel the sliding phase exists only inside a certain window of electron densities that has similarities with a pressure dependence of conductivity in organic conductors. Our studies show emergence of dynamical glassy phase in a purely periodic potential in the absence of any disorder that can explain enormously slow variations of resistivity in organic conductors. Finally we discuss the KAM concept of superfluidity induced by repulsive Coulomb interaction between electrons. We argue that the transition from the sliding KAM phase to the pinned Aubry phase corresponds to the superfluid-insulator transition.

Ether-functionalized pyrazolium ionic liquids as new electrolytes for lithium battery

Two new functionalized ILs based on pyrazolium cations and bis(trifluoromethylsulfonyl)imide anions (TFSI−) were synthesized and characterized. Their physicochemical and electrochemical properties, including melting point, thermal stability, density, viscosity, conductivity, and electrochemical window were investigated. The two ILs had low melting points and wide electrochemical windows. Behaviors of lithium redox, chemical stability against lithium metal, and charge–discharge cycle performance of lithium battery were also examined for the two IL electrolytes with 0.4molkg−1 LiTFSI. The IL electrolytes showed good chemical stability against lithium metal, and Li/LiFeO4 cells using the two IL electrolytes without additives owned good capacity and cycle property at the current rate of 0.1C.

Properties of an intermediate temperature ionic liquid NaTFSA–CsTFSA and charge–discharge properties of NaCrO2 positive electrode at 423 K for a sodium secondary battery

The physicochemical properties of an intermediate temperature ionic liquid (ITIL), NaTFSA (10mol%)–CsTFSA (90mol%) (TFSA=bis(trifluoromethylsulfonyl)amide), were investigated as a new electrolyte for a sodium secondary battery operating at elevated temperatures (around 423K). The viscosity, ionic conductivity, density and electrochemical window of this ITIL measured at 423K were 42.5cP, 12.1mScm−1, 2.29gcm−3 and 4.9V, respectively. The electrodeposition of metallic sodium at the cathode limit was confirmed by X-ray diffraction. The charge–discharge properties of a NaCrO2 positive electrode in this ITIL at 423K were investigated. The discharge capacities at constant current rates of 10mAg−1 (after 10 cycles) and 100mAg−1 (after 50 cycles) were 83.0 and 66.4mAhg−1, respectively. Except for the initial few cycles, the coulombic efficiencies were higher than 99.5% during the charge–discharge tests, which indicates that the Na/NaTFSA–CsTFSA/NaCrO2 cell is promising as a new type of sodium secondary battery operating at intermediate temperatures.

Study on Well-Kill Calculation Model with Deep-Water Engineer’s Method

With the growing demand for oil and gas resources of China, exploration and development face more complex situation and there is an urgent need to move to (deeper than 1000m) deep sea oil and gas exploration and development. As the density window for safe drilling fluid is narrow, the mud line is in high pressure and low temperature environment, and the cycle pressure loss in choker line is larger and other characteristics, Well-kill calculation model with deep-water engineer’s method is disparate with that for land. To this end, combined with the special formation conditions in deep water well control and the characteristics of long choke line, on the basis of considering the impact of the friction of choker line, gas compressibility factor, temperature and other parameters on the casing pressure and stand-pipe pressure, well-kill pressure parameters (including stand-pipe pressure, casing pressure, maximum casing pressure, etc.) calculation model of deep-water engineer’s method is established to carry out example calculation, which has directive significance for on-site well-kill construction.

Functionalized ionic liquids based on guanidinium cations with two ether groups as new electrolytes for lithium battery

Two new functionalized ionic liquids (ILs) based on guanidinium cation with two ether groups and TFSA − anion are synthesized and characterized. Their physicochemical and electrochemical properties, including melting point, thermal stability, density, viscosity, conductivity, and electrochemical window are determined. Both the ILs are liquids at room temperature, and the viscosities are about 60 mPa s at 25 °C. Behavior of lithium redox, chemical stability against lithium metal and charge–discharge characteristics of lithium battery, are also examined for the two ILs as electrolyte with 0.6 mol kg −1 LiTFSA. Though the cathodic limiting potentials of the two ILs are higher than 0 V versus Li/Li +, the lithium plating and stripping on Ni electrode can be observed in the two IL electrolytes, indicating their good chemical stability against lithium metal. Li/LiFePO 4 cells using the two IL electrolytes without any additive showed good cycle property at the current rate of 0.2 C at 25 °C and 55 °C.

Enhanced growth and recombinant protein production of Escherichia coli by a perfluorinated oxygen carrier in miniaturized fed-batch cultures

BackgroundLiquid perfluorochemicals (PFCs) are interesting oxygen carriers in medicine and biotechnology with a high solubility for oxygen. They have been repeatedly used for improving oxygen transfer into prokaryotic and eukaryotic cell cultures, however their application is still limited. Here we show the great benefit of air/oxygen saturated perfluorodecalin (PFD) for high cell density cultivation of Escherichia coli in microwell plates and their positive effect on the soluble production of a correctly folded heterologously expressed alcohol dehydrogenase.ResultsIn EnBase® cultivations the best effect was seen with PFD saturated with oxygen enriched air (appr. 10 μM oxygen per ml) when PFD was added at the time of induction. In contrast the effect of PFD was negligible when it was added already at the time of inoculation. Optimisation of addition time and content of loaded oxygen into the PFD resulted in an increased the cell density by 40% compared to control cultures, and correspondingly also the product yield increased, demonstrated at the example of a recombinant alcohol dehydrogenase.ConclusionsPFCs are a valuable additive in miniaturized cell culture formats. For production of recombinant proteins in low cell density shaken cultures the addition of oxygen-enriched PFD makes the process more robust, i.e. a high product yield is not any more limited to a very narrow cell density window during which the induction has to be done. The positive effect of PFD was even more obvious when it was added during high cell density cultures. The effect of the PFD phase depends on the amount of oxygen which is loaded into the PFD and which thus is a matter of optimisation.