乍得西南部中新生代火山作用与盆地演化

Located in the Central and West African, Chad, which is not well geological explored, is characterized by Mesozoic- Cenozoic intra-continental rift basins. The boreholes exposed that, during Mesozoic-Cenozoic times, volcanic activities were intense in these basins, but study on volcanic rocks is very weak, especially on those embedded in rift basins, and so far systematic and detailed work has still no carried out. Based on the project of China National Oil and Gas Exploration and Development Corporation, “The analysis of reservoir condition and the evaluation of exploration targets of seven basins in block H in Chad”, and the cooperative project between Institute of Geology and Geophysics, CAS and CNPC International (Chad) Co. Ltd., “Chronology and geochemistry studies on Mesozoic-Cenozoic volcanic rocks from southwestern Chad Basins”, systematic geochronology, geochemistry and Sr-Nd-Pb isotopic geochemistry studies on volcanic rocks from southwestern Chad basins have been done in the thesis for the first time. Detailed geochronological study using whole-rock K-Ar and Ar-Ar methods shows the mainly eruption ages of these volcanic rocks are Late Cretaceous- Paleogene. Volcanic rocks in the well Nere-1 and Figuier-1 from Doba basin are products of the Late Cretaceous which majority of the K-Ar (Ar-Ar) ages fall in the interval 95-75 Ma, whereas volcanic rocks in the well Ronier-1 from Bongor Basin and the Well Acacia-1 from Lake Chad Basin formed in the Paleogene which the ages concentrated in 66-52Ma. Two main periods of volcanic activity can be recognized in the study area, namely, the Late Cretaceous period and the Paleogene period. Volcanic activities have a general trend of south to north migration, but this may be only a local expression, and farther future studies should be carried on. Petrology study exhibits these volcanic rocks from southwestern Chad basins are mainly tholeiitic basalt. Major- and trace elements as well as Sr-Nd-Pb isotopic geochemistry studies show that the late Cretaceous and the Paleogene basalts have a definitely genetic relationship, and magmas which the basalts in southwestern Chad basins derived from were produced by fractional crystallization of olivine and clinopyroxene and had not do suffered from crustal contamination. These basalts are prominently enriched light rare earth elements (LREE), large-ion lithophile elements (LILE) and high field strength elements (HFSE) and depleted compatible elements. They have positive Ba, Pb, Sr, Nb, Ta, Zr, Hf anomalies and negative Th, U, P,Y anomalies. It is possible that the basalts from southwestern Chad basins mainly formed by mixing of depleted mantle (DM) and enriched mantle (EMⅡ) sources. The late Cretaceous basalts have higher (87Sr/86Sr)i ratios than the Paleogene basalts’, whereas have lower (143Nd/144Nd)i ratios than the latter, showing a significant temporal evolution. The mantle sources of the Late Cretaceous basalts may have more enriched mantle(EMⅡ) compositions, whereas those of the Paleogene basalts are relatively more asthenospheric mantle (DM) components. The mantle components with temporal change observed in basalts from Chad basins were probably correlated with the asthenospheric mantle upwelling and lithospheric thinning in Central and Western Africa since Mesozoic. Mesozoic- Cenozoic Volcanism in Chad basins probably is a product of intra- plate extensional stress regime, corresponded to the tectonic setting of the whole West and Central African during Cretaceous. Volcanism is closely correlated with rifting. As time passed from early period to late, the basaltic magma of Chad basins, characterized with shallower genetic depth, higher density and smaller viscosity, probably indicates the gradual strengthening evolution of the rifting. In the initial rife stage, volcanic activities are absent in the study area. Volcanic activities are basiccally corresponded with the strong extensional period of Chad basins, and the eruption of basalts was slightly lagged behind the extensional period. In the post-rift stage (30-0Ma), these basins shifted to the thermal sag phase, volcanic activities in the study area significantly decreased and then terminated.

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

Microgravity Smoldering Combustion Of Flexible Polyurethane Foam With Central Ignition

Smoldering constitutes a significant fire risk both in normal gravity and in microgravity. This space experiment has been conducted aboard the China Recoverable Satellite SJ-8 to investigate smoldering characteristics of flexible polyurethane foam with central ignition in a forced flow of oxidizer. This configuration resulted in a combination of opposed and forward flow smolder. The microgravity experiment is rather unique in that it was performed at constant pressure, and with a relatively high ambient oxygen concentration (35% by volume). The smoldering characteristics are inferred from measurements of temperature histories at several locations along the foam sample. Particularly important is the discovery that there is a transition from smoldering to flaming near the sample end in the opposed smoldering. This transition seems to be caused by strong acceleration of the smoldering reaction. The observed transition serves to initiate a vigorous forward-propagating oxidation reaction in the char left behind by the smoldering reaction. The secondary char oxidation reaction propagates through the sample and consumes most of the remaining char. In forward flow smoldering, the oxidizer depletion by the upstream opposed smolder prevents an exothermic oxidation reaction from being established in the foam until this preceding reaction is completed. Once fresh oxidizer flows in the sample, the existing conditions are sufficient for a self-sustained forward smoldering reaction to take place.