| Tarim basin is a huge superimposed basin in northwestern China which experiences multi-stage tectonics and is of great potential of hydrocarbon resources. Tazhong area is located in the middle of the central uplift belt, which is one of the three biggest palaeohigh; Yubei area is located in the eastern part of Maigaiti slope. Multisource, multistage tectonic movements and multiple recharging have caused the complex characteristics of Ordovician crude oil in these regions. Moreover, multiple recharging and reservoir adjustment have also caused the different accumulation mechanisms between the Tazhong and Yubei areas.In this study, Lianglitage Formation and Yingshan Formations of Ordovician in Tazhong and Yubei areas were selected. The study aimed to unveil the causes and mechanisms of oil and gas migration, and to set up different patterns for hydrocarbon accumulation in varied regions. The study took ancient fluid investigation as the original focus, and then expended it to generation, migration, time and space distribution of ancient fluid, and periods of hydrocarbon accumulating in different structural belts, by incorporating previous research results on well drilling, logging and formation evaluation, as well as burial history and thermal history analysis. Through a multi-disciplinary approach including petroleum geology, petroleum tectonics, reservoir geology, fluid mechanics, geochemistry, and hydrocarbon accumulation dynamics, a series of studies, such as SRXRF (Synchrotron Radiation X-ray Fluorescence) and fluid inclusion analysis (diagenesis observation, fluorescent observation, micro beam fluorescence spectrometry, homogenization temperature, freezing point test), have been conducted.The SRXRF (Synchrotron Radiation X-ray Fluorescence) is a light source with continuous tunable wavelengths from visible light to X-ray region, which has the advantages of high strength, good prospective laymen, polarization, continuously adjustable wavelength, short testing time, and no destruction caused to samples. This method has higher sensitivity and ability of detailed microanalysis, which other light source can’t meet. In this research, the elements were determined by measuring the characteristic X-ray energy of trace elements in crude oil; and their concentration were analyzed, quantitatively or semi-quantitatively, by calculating the area of characteristic X-ray spectrum. In this thesis, the relative concentrations of trace elements in 15 Ordovician crude oil samples of Yubei and Tazhong areas have been measured through SRXRF method. Based on these, the study have divided the crude oil samples into three categories: I, high V low Ni, rich in Ca, Zn, Mn trace elements, similar to marine crude oil; Ⅱ, low V high Ni, poor in Ca, Zn, Mn trace elements, rich in Fe trace element, similar to "continental" crude oil, possibly affected by the igneous activity; III, with the transition characteristics of the two above-mentioned types, this type of crude oil was possibly formed by mixing of types I and II oil. Moreover, the study also adopted the V, Ni ratio, V/ (V+Ni), which was used to indicate the oxidation and reduction condition of water body. V/(V+Ni)> 0.46 indicates the anoxic environment water; V/(V+Ni)<0.46 indicates the oxygen-rich environment water. Through the V/(V+Ni) analysis in crude oil samples of Ordovician of Tazhong and Yubei areas, V/(V+Ni)>0.46 could be found in oil samples from YB1-2X, YB1-3H wells in Yubei area and SX1, Shun7 wells in Tazhong area, indicating an anoxic environment. The results may correspond to Cambrian-lower Ordovician hydrocarbon source rocks; V/(V+Ni)<0.46 could be found in oil samples from YB1-4 well, indicating an oxygen-rich environment, corresponding to middle-upper ordovician hydrocarbon source rocks.Tazhong area is located in a special tectonic location:Manjiaer sag at the east, Awati sag at the west, Tabei uplift at the north, and Tazhong uplift at the south. It has very complicated accumulation conditions. Fractures orientation is majorly towards Northwest, which indicates that the development of fractures are closely related to Tazhong 1 fault zone formed during the middle Caledonian. Shunxi area is in tectonic low position, of which the near-surface karstification is not strong at I, III episodes of middle Caledonian and late Hercynian, the solution cave is undeveloped, and the reservoir condition is poor. The uplift continued to the end of the late Hercynian, and then deceased after the late stage of Hercynian. The current tectonics in Yubei area was affected by multiple tectonic movements, which mainly developed four sets of the fracture structure with different orientations. The eastern part of Yuzhong structural belt trends to the nearly EW direction, while the western part trends to NW direction. The overall of Yuzhong structural belt is an arc protruding southward; The Pishanbei 3 fault zone is in the NNW direction. The Yubei 1 well structural belt, Yubei 3 well structural belt and Yubei 3 well western structural belt are in NE direction. Yubei 1 well western structural belt, Yubei 1 well eastern structural belt (Madong structural belt), Yubei 3 well western structural belt and Yubei 4 well structural belt are NNE direction. The tectonic patterns in eastern Yubei area are more complex, while in the western part, the patterns are relatively simpler. Through the horizontal zoning research in structural patterns in Yubei area, it can be summarized that the main tectonic patterns of Yubei area include low, medium, and high angle thrust fault extension of fold, medium-high angle pressure shear structure, bidirectional thrust structure, thrust triangle structure, diapir, imbricate thrust structure, et.With the application of system analysis of fluid inclusion, combining with burial history and thermal history of each well, this study has confirmed that the Ordovician of both Shunxi and Yubei in Tazhong area develops three episodes two stages of oil and gas accumulation. For Shunxi area, the first stage was between 460.5 and 37.0Ma, and the second stage was 324.0 and 225.OMa, while for Yubei area, the first stag is between 275.0 and 240.OMa and the second stage is between 18.0 and 0.4Ma. Combining the research results of reservoir characterization, oil and source rock comparison, tectonic evolution, oil migration pathways, oil and gas recharge stages and periods, it indicates that Shunxi in Tazhong area mainly developed late Caledonian-early Hercynian and late Hercynian periods oil and gas accumulation; Yubei area mainly developed late Hercynian and late Himalayan periods oil and gas accumulation.This thesis has these innovation points indicated below:(1) The study has used SRXRF (synchrotron radiation X-ray fluorescence) technology to analyze trace elements in crude oil of the Ordovician Tazhong and Yubei areas, and combined results from fluorescent observation, the main peak wavelength of Fluorescence spectra of crude oil and oil fluid inclusions, to analyze the characteristics of different types of crude oil, and to preliminarily classify source of oil and gas.(2) The study has analyzed the accumulation processes of Ordovician in Tazhong and Yubei areas, investigated the causes of the differences of tectonic evolution and oil and gas accumulation periods, studied the differences in accumulation mechanism, and establish diversity pattern of hydrocarbon accumulation of Ordovician in Tazhong and Yubei areas. |
PDF Full Text Request