Research On Tectonic Stress Fields Of Hydrocarbon Reservoir In Buried Hills

Currently, the development pace of petroleum industry in China is far from meeting the needs of high velocity of national economy. China has to pay foreign currency to the amount of tens of billion Yuan to import petroleum every year. Hence the petroleum industry of China confronts new challenge. In view of the fact that petroleum reservoir in the buried hills is widely located, which characterizes enriching hydrocarbon, high yield, thick oil layers, large amount of production in a single drilling etc. The predominant cost-effective property has been proved by the practice of hydrocarbon exploration in the Eastern China of late years. Therefore, the second time of pioneering efforts in petroleum industry of China should take Tertiary hydrocarbon reservoir, especially the reservoir in buried hills as a break-through point.However the study on buried hills is not sufficient and many hard problems remain to be solved, particularly in reservoir studies. Fractures in hydrocarbon reservoir of buried hills are the most important reserving space. Especially in the buried hills that are based on the metamorphic or volcanic rocks, tectonic fractures are the principal reserving space for hydrocarbon. Consequently, predication of fracturing belts becomes the key point in the study on the reservoir of buried hills. However, because of the irregularity that the fractures appear both horizontally and vertically, neither the area and height of traps nor the hydrocarbon reserves is easy to determine. Meanwhile the drilling setting is also hard to arrange. Under this situation, introducing new fracture exploration methods for comprehensive research is imperative.Although the formation of fractures is subject to multiple factors such as lithological characters and attitudes etc., the distribution of tectonic stress fields plays an important role. Tectonic stress fields control all levels of events during the evolution of tectonic geology and this kind of function acts through the geological process. In regard to hydrocarbon reserves, tectonic stress fields play an essential role not only in hydrocarbon-generation of organic matter but also in the formation of reservoir fractures in buried hills. Consequently, the inversion of paleo-tectonic stress fields is a key technique for research of hydrocarbon reservoir in buried hills.This paper in the first time chooses the displacement amount of faults in the buried hills as boundary conditions arid adopts the finite element method to inverse paleo-tectonic stress fields. Through the research practice in Chengbei 30 Buried Hill, Buried Hill Zone in Damintun Depression and Hainan-Yuedong Buried Hill, a set of effective exploration schemes have been developed. Based on the features of each study area, different research schemes are used to inverse the distribution of paleo-tectonic stress fields. In terms of the inversion results, together with other geologic, logging and seismic data, this thesis has made geological assessment for each area. In the study to the buried hills in Hainan-Yuedong, this thesis emphasizes the control of paleo-tectonic stress field over development zones of fractures and identifies weathering crust on the top of buried hills and the tectonic fracture zones. The distribution pattern of zone is also estimated in line with the distribution of paleo-tectonic stress fields. In the study to Chengbei 30 Buried Hill, the feature of hydrocarbon accumulation is appraised through reconstructing paleo-tectonic stress fields in the buried hills and favorable trap zones are marked. Moreover, in the study to Damingtun Depression, by adopting finite element inversion method to study paleo-tectonic stress fields, the tectonic evolution history in the depression is deduced. On this basis, favorable blocks are divided and the hydrocarbon migration mode is also predicated. Several petroleum companies have adopted the achievement of this thesis and their exploration practice shows the research conclusion of this thesis is correct.In the thesis, the control function of paleo-tectonic stress fields over the hydrocarbon reservoir in the buried hills is summed up through the study to the above-mentioned areas. Firstly, the paleo-tectonic stress provides enough energy for organic matter to turn into hydrocarbon, and becomes an important factor during the hydrocarbon-forming process. Secondly, the path of hydrocarbon migration is always along the least resisted one; namely migration from high pressure area to low pressure area, and finally accumulate to form reservoir: in the low pressure traps. Therefore, the distribution of paleo-tectonic stress fields possesses important action. Thirdly, the reserving space of hydrocarbon in the buried hills is chiefly in the form of fractures. Moreover, tectonic fracture itself is not only excellent storage space, but also facilitate the development of corroded fissure. Therefore, the distribution of paleo-tectonic stress fields is one of key technology of petroleum exploration in the hydrocarbon field of buried hills.The research of this thesis relied on entrusted scientific projects, so the research itself is the main body of the scientific project and also tested by the exploration practice. The exploration result reveals that the finite element method, in the study of reversion to fossil-tectonic stress fields, is applicable and correct.