特大地震激发地球自由振荡的数值模拟研究

Large earthquakes, such as the Chile earthquake in 1960 and the Sumatra-Andaman earthquake on Dec 26, 2004 in Indonesia, have generated the Earth’s free oscillations. The eigenfrequencies of the Earth’s free oscillations are closely related to the Earth’s internal structures. The conventional methods, which mainly focus on calculating the eigenfrequecies by analytical ways, and the analysis on observations can not easily study the whole processes from earthquake occurrence to the Earth’s free oscillation inspired. Therefore, we try to use numerical method incorporated with large-scale parallel computing to study on the Earth’s free oscillations excited by giant earthquakes. We first give a review of researches and developments of the Earth’s free oscillation, and basical theories under spherical coordinate system. We then give a review of the numerical simulation of seismic wave propagation and basical theories of spectral element method to simulate global seismic wave propagation. As a first step to study the Earth’s free oscillations, we use a finite element method to simulate the propagation of elastic waves and the generation of oscillations of the chime bell of Marquis Yi of Zeng, by striking different parts of the bell, which possesses the oval crosssection. The bronze chime bells of Marquis Yi of Zeng are precious cultural relics of China. The bells have a two-tone acoustic characteristic, i.e., striking different parts of the bell generates different tones. By analysis of the vibration in the bell and the spectrum analysis, we further help the understanding of the mechanism of two-tone acoustic characteristics of the chime bell of Marquis Yi of Zeng. The preliminary calculations have clearly shown that two different modes of oscillation can be generated by striking different parts of the bell, and indicate that finite element numerical simulation of the processes of wave propagation and two-tone generation of the chime bell of Marquis Yi of Zeng is feasible. These analyses provide a new quantitative and visual way to explain the mystery of the two-tone acoustic characteristics. The method suggested by this study can be applied to simulate free oscillations excited by great earthquakes with complex Earth structure. Taking into account of such large-scale structure of the Earth, small-scale low-precision numerical simulation can not simply meet the requirement. The increasing capacity in high-performance parallel computing and progress on fully numerical solutions for seismic wave fields in realistic three-dimensional spherical models, Spectral element method and high-performance parallel computing were incorporated to simulate the seismic wave propagation processes in the Earth’s interior, without the effects of the Earth’s gravitational potential. The numerical simulation shows that, the results of the toroidal modes of our calculation agree well with the theoretical values, although the accuracy of our results is much limited, the calculated peaks are little distorted due to three-dimensional effects. There exist much great differences between our calculated values of spheroidal modes and theoretical values, because we don’t consider the effect the Earth’ gravitation in numerical model, which leads our values are smaller than the theoretical values. When , is much smaller, the effect of the Earth’s gravitation make the periods of spheroidal modes become shorter. However, we now can not consider effects of the Earth’s gravitational potential into the numerical model to simulate the spheroidal oscillations, but those results still demonstrate that, the numerical simulation of the Earth’s free oscillation is very feasible. We make the numerical simulation on processes of the Earth’s free oscillations under spherically symmetric Earth model using different special source mechanisms. The results quantitatively show that Earth’s free oscillations excited by different earthquakes are different, and oscillations at different locations are different for free oscillation excited by the same earthquake. We also explore how the Earth’s medium attenuation will take effects on the Earth’s free oscillations, and take comparisons with the observations. The medium attenuation can make influences on the Earth’s free oscillations, though the effects on lower-frequency fundamental oscillations are weak. At last, taking 2008 Wenchuan earthquake for example, we employ spectral element method incorporated with large-scale parallel computing technology to investigate the characteristics of seismic wave propagation excited by Wenchuan earthquake. We calculate synthetic seismograms with one-point source model and three-point source model respectively. Full 3-D visualization of the numerical results displays the profile of the seismic wave propagation with respect to time. The three-point source, which was proposed by the latest investigations through field observation and reverse estimation, can better demonstrate the spatial and temporal characteristics of the source rupture processes than one-point source. Primary results show that those synthetic signals calculated from three-point source agree well with the observations. This can further reveal that the source rupturing process of Wenchuan earthquake is a multi-rupture process, which is composed by at least three or more stages of rupture processes. In conclusion, the numerical simulation can not only solve some problems concluding the Earth’s ellipticity and anisotropy, which can be easily solved by conventional methods, but also finally solve the problems concluding topography model and lateral heterogeneity. We will try to find a way to fully implement self-gravitation in spectral element method in future, and do our best to continue researching the Earth’s free oscillations using the numerical simulations to see how the Earth’ lateral heterogeneous will affect the Earth’s free oscillations. These will make it possible to bring modal spectral data increasingly to bear on furthering our understanding of the Earth’s three-dimensional structure.

准噶尔盆地三个泉凸起油气成藏条件及动力学研究

Sangequan Uplift in Junggar Basin is an inherited positive structure, which has undergone many times of violent tectonic movements, with high tectonic setting, and far away from the oil-source sag, reservoir forming condition is complex. Combining sequence stratigraphy, depositional facies, reservoir formation theory with seismic and well logging analysis, this paper conducted integrated study on the hydrocarbon migration, accumulation, entrapment conditions, the reservoir forming dynamics and the forming model, and acquired the following recognition: (1) The special reservoir formation conditions that enable Sangequan Uplift to form a giant oil-gas field of over 100 million tons of reserves are as follows: (D Deltaic frontal sandbody is developed in Jurassic Xishanyao Formation, Toutunhe Formation and Lower Cretaceous Hutubihe Formation, with good reservoir quality;? Abundant hydrocarbon resources are found in Western Well Pen-1 Sag, which provides sufficient oil sources for reservoir formation of Sagequan Uplift; ?The unconformity-fault-sandbody system has formed a favorable space transporting system and an open conduit for long-distance hydrocarbon migration; ?fault, low amplitude anticline and lithological traps were well developed, providing a favorable space for hydrocarbon accumulation. (2) The most significant source beds in the Western Well Pen-1 Sag are the Mid-Permian Lower Wuerhe Formation and Lower-Permian Fengcheng Formation. The oil in the Well Block Lu-9 and Shinan Oilfield all originated from the hydrocarbon source beds of Fengcheng Formation and Lower Wuerhe Formation in the Western Well Pen-1 Sag and migrated through Jidong and Jinan deep faults linking unconformity of different regions from sources to structural highs of the uplift and shallow horizons. (3) There were 2 reservoir formation periods in District Sangequan: the first was in late Cretaceous during which the upper part of Xishanyao Formation and Toutunhe Formation; the second was in Triassic, the main resources are high-maturity oil and gas from Fengcheng Formation and Wuerhe Formation in Western Pen-1 Well sag and the gas from coal measure strata of Xishanyao Formation, that were accumulated in Hutubihehe Formation. (4) Model of the hydrocarbon migration, accumulation, reservoir formation of the study area are categorized as three types starting from the hydrocarbon source areas, focusing on the faults and unconformity and aiming at reservoirs: ① Model of accumulation and formation of reservoir through faults or unconformities along the "beam" outside source; ②Model of migration, accumulation and reservoir formation through on-slope near source;③Model of migration, accumulation and reservoir formation of marginal mid-shallow burial biogas-intermediate gas. (5) Pinchout, overlap and lithologic traps are developed in transitional zones between Western Well Pen-1 sag and Luliang uplift. Many faulted blocks and faulted nose-like traps are associated with large structures on Sangequan uplift. Above traps will be new prospecting areas for further hydrocarbon exploration in future.

苏丹被动裂谷盆地的油气成藏机理和成藏模式

The research area of this paper covers the maximum exploration projects of CNPC, including Blocks 1/2/4 and Block 6 of the Muglad basin and the Melut basin in Bocks 3/7 in Sudan. Based on the study of the evolution history of the Central African Shear Zone (CASZ), structural styles and filling characteristics of the rift basins, it is put forward that the rift basins in Sudan are typical passive rift basins undergoing the strike-slip, extension, compression and inversion since the Cretaceous. The three-stage rift basins overlapped obliquely. The extension and rifting during the Early Cretaceous is 50-70% of the total extension. The features of the passive rift basins decided that there is a single sedimentary cycle and one set of active source rocks within the middle. Influenced by the three-stage rifting and low thermal gradient, hydrocarbon generation and charging took place very late, and the oil pool formation mechanism is very unique from the Lower Cretaceous rift sequences to the Paleogene. The reservoir-seal assemblages are very complicated in time and space. The sealing capacity of cap rocks was controlled by the CASZ. In general the oils become heavier towards the CASZ and lighter far away. The oil biodegradation is the reason causing the high total acid number. The determination of effective reservoir depth ensures that all discovered fields up to now are high-production fields. The propagation and growth of boundary faults in the rift basins can be divided into a simple fault propagation pattern and a fault growth-linkage pattern. It is firstly found that the linkage of boundary fault segments controls the formation of petroleum systems. Three methods have been established to outline petroleum systems. And a new classification scheme of rift-type petroleum system has been put forward: pre-rift, syn-rift (including passive and active) and post-rift petroleum systems. This scheme will be very important for the further exploration of rift basins. This paper firstly established the formation models of oil pools for the passive rift basins in Sudan: the coupling of accommodation zones and main plays for the formation of giant fields. The overlapping of late rifting broke the anticlines to be several fault-blocks. This process determined that anti-fault blocks are the main traptypes in the cretaceous sequences and anticlines in the Paleogene. This can explain why the traptypes are different between the Muglad and Mefut basins, and will provide theoretic guidance for the exploration strategy. The established formation mechanism and models in this paper have had great potential guidance and promotion for the exploration in Sudan, and resulted in significant economic and social benefit. A giant field of 500 million tons oil in place was found 2003. The cost in Blocks 3/7 is only 0.25

油藏数值模拟中的网格粗化和细化技术研究

The grid is a foundation of reservoir description and reservoir simulation. The scale of grid size is vital influence for the precision of reservoir simulation the gridding of reservoir parameters require reasonable interpolation method with computing quickly and accurately. The improved distant weighted interpolation method has many properties, such as logical data points selection, exact interpolation, less calculation and simply programming, and its application can improve the precision of reservoir description and reservoir simulation. The Fractal geologic statistics describes scientifically the distribution law of various geological properties in reservoir. The Fractal interpolation method is applied in grid interpolation of reservoir parameters, and the result more accorded with the geological property and configuration of reservoir, and improved the rationality and quality of interpolation calculation. Incorporating the improved distant weighted interpolation method with Fractal interpolation method during mathematical model of grid-upscaling and grid-downscaling, the softwares of GROUGH(grid-upscaling) and GFINE (grid-downscaling) were developed aiming at the questions of grid-upscaling and grid-downscaling in reservoir description and reservoir simulation. The softwares of GROUGH and GFINE initial applied in the research of fined and large-scale reservoir simulation. It obtained fined distribution of remaining oil applying grid-upscaling and grid-downscaling technique in fined reservoir simulation of Es21-2 Shengtuo oilfield, and provided strongly and scientific basis for integral and comprehensive adjustment. It's a giant tertiary oil recovery pilot area in the alkaline/surfactant/polymer flooding pilot area of west district of Gudao oilfield, and first realized fined reservoir simulation of chemical flooding using grid-upscaling and grid-downscaling technique. It has wide applied foreground and significant research value aiming at the technique of grid-upscaling and grid-downscaling in reservoir description and reservoir simulation.