Genetic types and distribution of shallow-buried natural gases

Great volumes of shallow-buried （〈2,000 m） natural gases which are mainly composed of biogases and low-mature gases have been found in the Mesozoic-Cenozoic sedimentary basins in China. Many shallow gas reservoirs in China are characterized by coexistence of biogas and low-mature gas, so identifying the genetic types of shallow gases is important for exploration and development in sedimentary basins. In this paper, we study the gas geochemistry characteristics and distribution in different basins, and classify the shallow gas into two genetic types, biogas and low-mature gas. The biogases are subdivided further into two subtypes by their sources, the source rock-derived biogas and hydrocarbon-derived biogas. Based on the burial history of the source rocks, the source rock-derived biogases are divided into primary and secondary biogas. The former is generated from the source rocks in the primary burial stage, and the latter is from uplifted source rocks or those in a secondary burial stage. In addition, the identifying parameters of each type of shallow gas are given. Based on the analysis above, the distributions of each type of shallow gas are studied. The primary biogases generated from source rocks are mostly distributed in Quaternary basins or modem deltas. Most of them migrate in watersoluble or diffused mode, and their migration distance is short. Reservoir and caprock assemblages play an important role in primary biogas accumulation. The secondary biogases are distributed in a basin with secondary burial history. The oil-degraded biogases are distributed near heavy oil pools. The low-mature gases are widely distributed in shallow-buried reservoirs in the Meso-Cenozoic basins.

Common reflection surface stack using dip decomposition for rugged surface topography

我们在场为任意的最高的表面地形学提供支持的普通思考表面(CRS ) 栈的扩展。没有对任何举起静电干扰的需要，叠的 CRS 能被用于原来的 prestack 数据。叠 CRS 的零偏移量的节能被改正(redatumed ) 到由运动学的波浪的给定的平面水平，地归因。地震处理结果显示 CRS 叠了节因为崎岖表面地形学比对 S/N 比率和思考事件的更好的连续性的常规叠的节好。就零偏移量的光线的多重路径而言，方法处理来自不同剧降的思考信息并且用剧降分解的方法执行栈，它改进 CRS 的运动学、动态的字符叠的节。

Distribution of sterane maturity parameters in a lacustrine basin and their control factors:A case study from the Dongying Sag,East China

Fifty samples from the source rocks in Member 3 and Member 4 of the Paleogene Shahejie Formation in the Bohai Bay Basin, East China, were analyzed to investigate the distribution, evolution of the molecular maturity ratios C29ββ/（ββ＋αα） and C2920S/（20S＋20R） and their control factors in the natural geological profile and sequence. The results showed that progressive changes in molecular maturity parameters are associated with major changes in thermal evolution of related biomarkers. Increases in the C29ββ/（ββ＋αα） and C2920S/（20S＋20R） ratios result from the difference in the relative rate between generation and thermal degradation of isomers involved. The samples from a hyper-saline environment below 3.5 km in which evaporitic rocks deposited shows high response of Sr/Ba, Sr/Ca, Fe/ Mn, Pr/n-C17, Ph/n-C18 and gammacerane and low response of Pr/Ph. There presents negative reversal of biomarker maturity C29ββ/（ββ＋αα, C29ββ/（ββ＋αα） and Ts/（Ts＋Ym） in the samples from hypersaline environment, reflecting that the gypsum- halite have negative effect on the isomerization of biomarker and thermal evolution of organic matter. The minerals in evaporites also retard the conventional thermal indicators including vitrinite reflectance （Ro） and pyrolysis peak temperature Tmax at the depth below 3.4 km （i.e. 〉3.4 km）, and these parameters also show the inhibition from overpressure in the range of 2.4-3.4 kin. This result will be helpful in the interpretation and application of molecular maturity parameters for similar saline lacustrine basins.

Characteristics and mechanism of low permeability beach-bar sandstone reservoir of Es4 in Dongying sag

Core and cast sections observation and description,and logging,scanning electron microscope and core lab analysis data etc. were applied to the present research of the characteristics and mechanism of low permeability beach-bar sandstone reservoir of Es4 in Dongying sag. The results indicated the reservoir has the characteristics of middle-low pores,low-permeability,low compositional and structural maturity,and thin throat. The low-permeability is mainly due to sedimentation (fine particles and argillaceous inter beds) and diagenesis (compaction,cementation,and dissolution). The cementation reduced the physical property of the reservoir mainly by carbonate cementation,quartz autogeny and enragement,and autogeny clay. Clay minerals usually jam the pores by filling holes,close-fitting the wall of hole,bridging,wrapping grains,and separate attaching the pores and so on. The dissolution is insufficient so as not to improve the porosity and permeability of the reservoir obviously. So it is also an important factor of forming low-permeability reservoir.

Application of the third generation of coherent cube in recognizing faults and fractures

Three-dimensional coherent cube is an extremely effective new technique for interpreting seismic data. It has obvious advantages in many aspects compared with the conventional 3D data volume, such as recognizing faults and fractures, interpreting ancient channels, and edge detection of oil-gas reservoir. Coherent cube is to condense and extract information around a certain point in 3D data volume, and then highlight the original characteristics of the geologic body at this point. Therefore, in terms of its essence, coherent cube is a special seismic attribute cube and those points having rather small coherent value are related to the discontinuity of geologic body. In practical production, people often interpret horizontal slices or layer slices of coherent cube, and this provides advantageous foundations for resolving special problems in oil-gas exploration.……

Experiment and Simulation of Large Capacity Air-guns in Deep Structure Exploration

The air-gun source has important applications as a new, environmentally, green active source in regional scale deep exploration. In the past, the air gun source was used mainly in small-scale, high-resolution shallow oil exploration, but has a lack of adequate research in deep exploration. In order to study the selection of work parameters and field conditions of the air gun source in deep exploration, this paper does the following work: ① analyze the characteristics of the air gun source using air gun experiments; ② simulate the air gun signal and air gun-array signal based on the theory of free bubble oscillation to analyze the influence of bubble oscillation and study the wavelet energy and spectrum characteristics needed in deep exploration; ③ on the basis of theoretical simulation, study the influence of work parameters, such as air-gun capacity, work stress and depth on air gun signal and analyze the influence of air-gun array inspired moment and spacing of different air guns on air gun-array signals; and ④ study energy reflection and transmission coefficients for different underwater interfaces, which is very useful for choosing suitable field conditions.

Origin of Subsequent Condensate Pool in Lunnan Low Uplift,Northwest China

Lunnan （轮南） low uplift,where developed amounts of condensate pools in both Ordovician and Carboniferous reservoirs,locates in the north uplift of Tarim basin,Northwest China.Lunnan area has experienced intensive gas invasion since the Himalayan movement,causing multiple types of accumulation coexisting in the Ordovician reservoir.Geochemical evidence shows that these condensate oils are of low maturity （vitrinite reflectance levels near 1.0%） and the dominant component of the condensate gas is dry gas （the content of CH4 over 94%）,which reflects that the condensate pool in Lunnan area is not the product of thermal cracking,but the subsequent accumulation derived from the phase fractionation.Furthermore,our observations on the C6-C7 hydrocarbons in Lunnan area are qualitatively similar to the effect of phase fractionation with condensates having higher paraffin and lower aromaticity than residual oils.Thus,two types of the condensates are defined by their phase behavior,which are saturated condensate pool and the nonsaturated one.The saturated condensate pool with an oil ring mainly developed in Ordovician reservoir,with large difference between formation pressure （FMP） and the dew point pressure （DPP）.The origin of these condensates is considered as the in-situ segregation triggered by the invasion of excessive dry gas.On the other hand,the nonsaturated condensate pool that almost existed in the Carboniferous reservoir is a hydrocarbon reservoir containing slight difference between FMP and DPP,without oil ring,and evaporative fractionation due to the fault movement controls its generation.