| 其他摘要 | The Dongying Depression is a part of the Bohaiwan rift basin. Different sizes of igneous rocks interbedded with sandstones and shales are found in its Tertiary, especially in the major hydrocarbon source rocks (ES3). Large quantities of oil are accumulated in the igneous rocks in basalt-source rocks and gabbro-source rocks. The oil-pool formation and distribution is not understood well, so that the exploration meets many difficulties. This dissertation discusses the genetic mechanism of hydrocarbon in the igneous-source rock assemblages, in that include volcanic minerals, transitional metal elements, and organic matter. Therefore are special geological and geochemical conditions in the assemblages during long-term burial history. The transitional metal elements and some of the volcanic minerals are able to accelerate hydrocarbon generation in the source rocks by catalysis. And organic acids from the source rocks are able to dissolve some basic minerals and the transitional metal elements in igneous rocks, which result in more reservoir spaces in the igneous rocks. Therefore, two different models of oil accumulation in basalt and gabbro developing areas are postulated, which will help oil exploration in the areas. Meanwhile, the dissertation also makes better understanding for oil origins and accumulations in the igneous rock developing areas in other rift basins. By analyses of the geological and geophysical data of the Dongying Depression, the author recognized that the igneous rocks were distributed close to the marginal faults of the Binxian High, the Guangrao High, and the Luxi Uplift in Tertiary. Volcanic activities appeared in the I (Ek-Ed) and II (N-Q) two cycles, which consisted of the I i(Ek), 12 (Es4), I 2(Es3), I 4(Es2), I 5(Esi),IIi(Ng) andII2(Nm) seven sub-cycles. All the igneous rocks can be divided into basalts and gabbrps, and are believed as alkali-subalkaline olivine basalt, trachyte and basalatite. The author suggests that igneous rocks in the Binnan, Gaoqing, and Chunxi areas are from same magma source in the mantle. The Chunxi basaltic rocks are formed by the mantle magma mixed with more crust materials. The basaltic rocks in the Binnan and Gaoqing areas are produced from the mantle magma with less mixed crust materials. Furthermore, the Binnan and Gaoqing area are relatively closer to the magma source area, so that repeated eruptions and many volcanoes are formed in the. deposition environment of hydrocarbon source rocks. Volcanic and thermal-water activities are beneficial to organic matter deposition and excellent source rock formation, because they make the lake-water warmer, and provides a lot of salts, minerals, and nutriments (such as N or P-containing materials) for the lake organisms, which leads to sedimentation of organic matter, carbonate and oil shale. Meanwhile, the transition elements (such as Ni, Co, V, Ti) and some volcanic minerals are spread in the source rocks, which will be catalyses to the hydrocarbon generation from organic matter. In long time burials, there are interactions between the volcanic materials (including the transitional metal elements and minerals) and organic matter in the source rocks. The author conducted a series of thermal stimulations on the source rocks with the Ni and Co catalysts, and represented that the hydrocarbon generation from the oil shales begins at 120 ℃, about 100 ℃ lower than the generation without the catalysts, and the quantity of the generated hydrocarbons are several times more than those without catalysts when stimulating temperature are in 200~280°C. Therefore, this paper concludes that the source rocks around basalts or gabbros generate much more oil and gas at much lower burial depths in a rift basin comparing with the source rocks far away from igneous rocks or not companying with volcanic rocks and thermal-water activities. Also in the burial the basalts and gabbros were dissolved obviously by organic acids from the source rocks, so that their pores and cracks were enlarged and become into good reservoir rocks. At same times, large quantity of hydrogen were released from dissolving of olivine, which come into the source rocks acting as hydrogenation to the hydrocarbon generation of the organic matter in the source rocks. In the early period of Ed, ES3 source rocks in the Lijin sag generated oils which migrated into the Binnan basalts through faults. The source rocks around the basalts generated oils by catalysis of the transition elements and volcanic minerals. These two kinds of oils accumulated in the dissolved pores of the basalts and carbonate breccias, so that oil pools were formed in the basalt-source rock assembly. In addition to oil generation in Lijin, the Niuzhuang sag also generated oil which accumulated in the Chunxi reserviors. At the end of Ed (24.1 ± 0.4Ma), basaltic magma invaded into the ES3 source rocks at the Chunxi area, which led to breaking of original oil-pools. After the magma cooling, oil from source rocks of the Lijin, Boxing and Chunxi areas migrated again into the cracks of the gabbros and the metamorphic rocks. Therefore, oil accumulation formed in the gabbro-source rock assemblage. Four creative viewpoints represent in the dissertation, which including (1) two igneous-source rock assemblages being postulated in the rift basin, and volcanic and thermal-water activities being beneficial to deposition of exllent source rocks in lacustrine environments; (2) transitional metals from volcanos being good catalysts to the hydrocarbon generation from organic matter, which was proved by thermal stimulations; (3) organic acids from the source rocks dissolving some minerals and extracting transitional metals from the igneous rocks, which is important mechanism of igneous reservoir formation; (4) two different oil-pool models builded for the igneous rock developing areas. |
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