The Coupling Relationship Between Differential Structural Evolution And Hydrocarbon Charging History In The Ordovician Of Tahe Oilfiled, Tarim Basin

Tarim basin is a huge superimposed basin in northwestern China which experiences multi-stage tectonics and is of great potential of hydrocarbon resources. Tahe oilfiled located at the structural slope of the Akekule uplift with complex petroleum accumulation history. The paleostructure ridge in Tahe oilfield experienced multi-stage migration and caused the distribution characteristics of karstic reservoir of Ordovician carbonate and hydrocarbon accumulation history were diversity in different areas in Tahe oilfield.Based on theories about tectonics, sedimentology, lithology, petroleum geology and reservoir geochemistry, this paper comprehensively uses data of geology, drilling, geophysics and geochemistry, takes fluid inclusion technique as the primary method and paleo-fluid evolution as breakthrough. Through the study of fluid inclusions from different areas of Ordovician carbonate confirm the hydrocarbon filling history and time. Combiling with the paleostrucure characteristic and evolution process to analysis how the migration of paleostructure ridge controls the development of karstic reservoir of Ordovician carbonate and the process of hydrocarbon migration and accumulation in Aiding, Yuqi and Tahe areas. According to the dissection typical petroleum reservoirs, it incorporateds result of adamantine index and migration tracing from petroleum inclusions and analyses controlling factors of reservoir conservation and accumulation. Finally, it preliminarily illustrates the hydrocarbon migration and accumulation models and their enrichment rules.For this study fluid inclusion petrography, microthermometry, transmitted light and micro fluorescence observation methods were employed to systematically obtain information on fluorescent colours of hydrocarbon inclusions, homogenization temperatures of oil inclusions and their coeval aqueous inclusions. The results indicate two to three events of oil charging and one gas charging event for the Ordovician carbonate reservoirs. The oil charging events have been reconstructed at433.3-420.2Ma and18.8-6.8Ma in Aiding area and463.2-452Ma, 132-94.9Ma and22-7.9Ma in Yuqi area, while the oil charging events in Tahe main area at449-411.3Ma and22.5-4.8Ma, gas charging event most likely occurred at the last event.The differential structural evolution characteristic in Akekule uplift shows that the paleostructure ridge in Tahe oilfield experienced multi-stage migration. And the paleokarstic reservoir and hydrocarbon filling history are different in Tahe oil field due to the paleostructure ridge transport. In the middle Caledonian period, the Aiding area was located at the high point of paleostructure ridge, and the Yuqi area and Tahe main area were located at the slope to basin area of paleostructure ridge, so the Aiding area was the paleokarst development area in the middle Caledonian. In the early hercynian period, the paleostructure ridge high point transfered to the Yuqi area, and the Aiding area and Tahe main area were at the slope part of the paleostructure ridge, so the Yuqi and Tahe areas were the main paleokarst development areas. In the late hercynian period, the paleostructure ridge continue migrated to the Tahe main area, the Aiding area was at the slope to basin area and Yuqi area was at the slope area of the paleostructure ridge. In the Indosinian-Yanshanian to Himalayan period, the paleostructure ridge did not change any more, and the Tahe main area was still at the structural high point, the Aiding and Yuqi area were at the slope of the paleostructure ridge.Source-petroleum correlation analysis and hydrocarbon generation and expelling history and the Q650/500factors indicate that petroleum in Tahe oilfield is originated from Cambrian-Lower Ordovician source rocks. By comprehensive analysis of global structure evolution, sedimentary system, migration tracing from petroleum inclusions, petroleum conduit system in Tahe oilfield is mainly composed of faults, unconformities, structure fracture and has different assembled relationship in different area.According to the dissection typical petroleum reservoirs, it incorporateds result of adamantine index and conservation condition from petroleum inclusions, which reveal that the Aiding block experienced the oil charging process in the middle Caledonian period, structure destruction and oil reservoir reconstruction in the early Hercynian period, and then underwent recharging and adjusted in the Himalayan period. The Ordovician reservoir in the Yuqi area experienced the oil charging process in the middle to late Caledonian period, primary damage in the early Hercynian, destruction and adjustment in the late Hercynian, weak recharging in the Indosinian-Yanshanian, oil and gas recharging and reconstruction in the Himalayan period. The Tahe main area experienced a long charging time from middle Caledonian to the early Hercynian, oil reservoir destruction and reconstruction in the early Hercynian period, hydrocarbon charging intermission in the Indosinian-Yanshanian, hydrocarbon recharging in the Himalayan. So the hydrocarbon charging time is early in the Aiding to Yuqi area, but the duration time is not long. The Ordovician oil and gas reservoir formed at the middle-late Caledonian suffered fresh water leaching and biodegration in the early Hercynian for the structural uplift. And then the normal oil reservoir changed into heavy oil reservoir, there were plenty residual bitumen. The oil charging time is late but the duration time is long in the main area of Tahe oil field, and the Ordovician reservoir reconstruction degree gradually decreased from north to south because the structural uplifting degree decreased from north to south. So we can conclude that the structure evolution and structure ridge migration control the oil and gas charging history and accumulation.Major innovation points of this paper are:(1) Using the microscopic evidence from fluid inclusion to reveal how the paleao structure ridge migration control the paleao karst reservoir distribution and oil and gas charging.(2) At both macro and micro angles, geologic integrated analysis and simulation experiment are combined to build hydrocarbon migration and accumulation models.