Discussion of the Mode and Mechanism of Oil and Gas Accumulation in the Nanbaxian Pool in the North of the Qaidam Basin

Because of the difference ofoil and gas accumulation condition between the hanging wall and the footwall of a fault, there is a peculiar accumulation mechanism that oil and gas mainly exists in the hanging wall of the basement fault, but in the footwall of the shallow detachment fault in the Nanbaxian pool. The oil and gas of the Nanbaxian pool came from the mature Jurassic hydrocarbon source rock of the Yibei depression located at the south of the Nanbaxian pool. Firstly, the oil and gas accumulated in the traps of the hanging wall of the basement fault by way of the unconformity and the basement faults, and turned into some primary deep pools; and then, the shallow detachment fault that formed in the later tectonic movement broke into the deep primary pools, which caused the oil and gas migration upwards along the basement faults and the shallow detachment faults and the evolvement into some secondary oil and gas pools later. The history of the Nanbaxian oil and gas accumulation can be summarized successively as the syndepositional upheaval controlled by faults; single hydrocarbon source rock; unconformities and faults as migration channels; buoyancy, overpressure and tectonic stress as dynamic forces; multistage migration and accumulation of oil and gas; and finally an overlapped double-floor pattern of oil and gas accumulation. The most important explorative targets in the north of the Qaidam Basin are traps connected with the primary pools in the footwall by shallow detachment faults.

Characteristics and accumulation mode of large-scale Sinian-Cambrian gas reservoirs in the Gaoshiti-Moxi region, Sichuan Basin

The Sinian-Cambrian formations of the Sichuan Basin have favorable hydrocarbon accumulation conditions,but the exploration for large-scale gas fields is quite challenging due to old strata and multiple tectonic movements.Since the Weiyuan Sinian large gas field was found in 1964,the largest monoblock gas field(Anyue Gasfield)was discovered in the Cambrian Longwangmiao Formation of the Moxi region in 2013 with proven gas reserves of 440.1×109 m3.Total proven,probable and possible reserves exceed one trillion cubic meters in the Sinian Dengying Formation and the Cambrian Longwangmiao Formation of the Gaoshiti-Moxi region.The natural gas components,light hydrocarbons,reservoir bitumen abundance and other evidences prove that the dry natural gas was mainly derived from oil-cracking,with methane(a content of 82.65%-97.35%),ethane(a content of 0.01%-0.29%),nitrogen(a content of 0.44%-6.13%),helium(a content of 0.01%-0.06%),and hydrogen sulphide(0.62-61.11 g/m^(3)).Gas reservoir pressure increases gradually from the Sinian normal pressure(a pressure coefficient of 1.07-1.13)to high pressure(a pressure coefficient of 1.53-1.70)in the Cambrian Longwangmiao Formation.The temperature of the gas reservoir is 137.5-163 ℃.Gas reservoir traps are divided into three categories:tectonic type,tectonic-formation type and tectonic-lithologic type.The large-scale enrichment of the Sinian-Cambrian natural gas results from effective configuration of the large stable inherited palaeo-uplift during the Tongwan tectonic movement,wide distribution of ancient source rocks,high-quality reservoirs with vast pore-cavity,crude oil cracking of large palaeo-reservoirs and favorable preservation conditions.According to the palaeo-structure pattern prior to crude oil cracking of the palaeo-reservoirs,and bitumen abundance as well as the distribution characteristics of current gas reservoirs,the accumulation patterns of the cracking gas reservoir can be classified into three types:accumulation type,semi-accumulation and semi-dispersion type,and dispersion type.This understanding will play an important role in guiding the exploration of the Sinian-Cambrian natural gas exploration in the Sichuan Basin.

Experimental investigation of limit space charge accumulation mode operation in a semi-insulating GaAs photoconductive semiconductor switch

Experiments with the limited space-charge accumulation（LSA） mode of oscillation in a large gap semiinsulating （SI） GaAs photoconductive semiconductor switch（PCSS） are discussed.It has been observed that growth and drift of a photo-activated charge domain（PACD） are quenched only when the bias voltage is more than twice the threshold voltage.The original negative resistance characteristics are directly utilized in the LSA mode;during LSA operation the spatial average of the electric field varies over a large portion of the negative differential mobility region of the velocity-electric field characteristic.The work efficiency of an SI GaAs PCSS is remarkably enhanced by electric field excursions into the positive resistance region when the total electric field is only below the threshold part of the time.The LSA mode can only operate in the certain conditions that satisfy the quenching of the accumulation layer and the smaller initial domain voltage.

Exploration of Subtle Trap in Jiyang Depression

This article analyses the procedure of exploration of the Tertiary subtle trap in Jiyang depression and divides the Tertiary subtle trap into 3 types (lithologic reservoir, stratigraphic reservoir and fractured reservoir) and 8 groups, then summarizes the common feature and founding discipline of the subtle trap and finds 4 accumulating modes including steep slope mode, depression mode, center anticline mode and gentle slope mode. Its main exploration methods are explicated from the viewpoint of reservoir geological modeling, description of recognizing traps and comprehensive evaluation of reservoir and so on.

Drive current of accumulation-mode p-channel SOI-based wrap-gated Fin-FETs

Comparisons are performed to study the drive current of accumulation-mode（AM） p-channel wrap-gated Fin-FETs.The drive current of the AM p-channel FET is 15%-26%larger than that of the inversion-mode （IM） p-channel FET with the same wrap-gated fin channel,because of the body current component in the AM FET, which becomes less dominative as the gate overdrive becomes larger.The drive currents of the AM p-channel wrap-gated Fin-FETs are 50%larger than those of the AM p-channel planar FETs,which arises from effective conducting surface broadening and volume accumulation in the AM wrap-gated Fin-FETs.The effective conducting surface broadening is due to wrap-gate-induced multi-surface conduction,while the volume accumulation,namely the majority carrier concentration anywhere in the fin cross section exceeding the fin doping density,is due to the coupling of electric fields from different parts of the wrap gate.Moreover,for AM p-channel wrap-gated Fin-FETs, the current in channel along 110 is larger than that in channel along 100,which arises from the surface mobility difference due to different transport directions and surface orientations.That is more obvious as the gate overdrive becomes larger,when the surface current component plays a more dominative role in the total current.

A novel GAAC FinFET transistor:device analysis, 3D TCAD simulation, and fabrication

We report the analysis and TCAD results of a gate-all-around cylindrical （GAAC） FinFET with operation based on channel accumulation. The cylindrical channel of the GAAC FinFET is essentially controlled by an infinite number of gates surrounding the cylinder-shaped channel. The symmetrical nature of the field in the channel leads to improved electrical characteristics, e.g. reduced leakage current and negligible corner effects. The Ion/Ioff ratio of the device can be larger than 106, as the key parameter for device operation. The GAAC FinFET operating in accumulation mode appears to be a good potential candidate for scaling down to sub-10 nm sizes.