The Paleogene Thermal Fluid Activities And Their Impact On Clastic Reservoir In Qikou Sag

The volcanic activities are very strong in Qikou and Beitang Sag since the Tertiary, so the volcanic rock is very developed in the sag, mainly with in shallow intrusions of diabase and other means output, and main composition of magma is CO2-rich volatile components. As early as the beginning of the 60s Dagang oil field had already started to study the volcanic reservoirs, After nearly half a century of exploration and development, they have found gs 7 well diabase oil reservoir, Zhang 7 contact metamorphic oil reservoir and kou 22 Well diabase volcanic oil reservoir in the region. Magmatic activities in this area can be seen have a very close relationship with the oil and gas accumulation. According to the use of petrography, geochemistry of volcanics, fluid inclusion and organic geochemical techniques, we mainly discussed the regional magmatic activities influence mechanisms and contributions on the reservoir physical properties, especially the deep reservoir physical properties.The Tertiary volcanic rocks of Qikou region is mainly a set of basalt - diabase series of basic volcanic and intrusive rocks. Horizontally, the Tertiary volcanic rocks is mainly in the junction of South Dagang buried hill tectonic belt and Zhang Dong fault belt , east of sanmu buried hill tectonic belt. Longitudinal direction, they are mainly distributed in 5 layer series, incuding Kongdian group, Shahejie group, Dongying group, Guantao group, Minghuangzhen group deposition etc.Through the study on geochemistry of volcanics, the volcanic rocks of the region show similar characteristics with Cenozoic volcanic rocks in the the eastern of our country, which are mainly enriched in lithophile elements and high field strength elements, not loss of Nb, Ta and other elements, show a clear OIB characteristics, while enrichment of Pb, showing interior rift basalts features. Mantle properties of Beitang sag may changed during the period of Es3-Es1, transforming from enriched mantle to depleted mantle. The chemical composition of volcanic rocks performs particularly, with the passage of time (Es3→Es1) , degree of alkaline of Tertiary volcanic rocks in the study area are more and more high, chemical composition is more and more rich in Na, poor in K.The rocks of the region is mainly composed by terrigenous clastic rock and Tertiary volcanic rocks, the particle size of terrigenous clastic rock is relatively coarse, manily with fine sandstone and medium sandstone. Diagenesis mainly contains compaction, pressure solution, cementation, replacement, alteration and dissolution. The sequence of diagenesises is: microcrystalline calcite→early quartz overgrowth→sparry calcite→authigenic sericite, authigenic muscovite, later quartz overgrowth→authigenic chlorite, alkali feldspar overgrowth→pore filling calcite. Diagenetic stage is maily at the A period of medium diagenesis. In Qikou Sag, the depth of transformation of diagenetic stage form the early diagenesis to medium diagenesis is 3351mBoth the shallow basic magmatic activity (<3500m) and deep thermal activity (> 3500m) from the upper mantle which is rich in CO2 fluid both have significantly improved the physical properties of the reservoir, but their impact mechanism has a great difference. The shallow magmatic hydrothermal activity is mainly caused by the intrusion of Tertiary mafic magma, the content of smectite and kaolinite at the layer where igneous rock body in place are higher than its adjacent layers. Deep thermal fluids is a major supercritical fluid, which is produced by partial melting of magma coming from lower crust or even the upper mantle. This supercritical thermal fluid has not only very high heat, but also better connectivity, which greatly increased the formation temperature of this area, and caused hydrothermal warming effect, formed large areas of abnormal high pressure zone, improved the deep reservoir physical properties. At the same time, the chemical composition of this thermal fluids is not only rich in halogen element, Fe, Si, Cu, Pb, Au, W and other elements, but also rich in CO2, H2O and other volatile components, all of which have important influence for the production of secondary porosity and improving the deep reservoir properties.