Study On Gas Accumulation Conditions Of Ordovician Majiagou Group In Northeastern Ordos Basin

Ordos Basin in the Neopaleozoic from the 1989 found Jingbian gas field, Jingbian gas field continues to expand the scale with in-depth exploration, not only weathered shell type gas reserves increased significantly and in a new layer system(combination of dolomite type) has also made a breakthrough. Shows the Neopaleozoic gas reservoir types has a good exploration prospect.On the basis of summarizing the previous research results, this paper analyzes the basic geological conditions of the study area, combined with the existing exploration results into the law of reservoir formation, and to evaluate the favorable area of reservoir formation. Of hydrocarbon source rock, reservoir conditions, cover, as well as traps, migration and preservation research. Analysis the main controlling factors and accumulation model, to predict the favorable area for reservoir area within the scope of natural gas accumulation. The following main results were obtained through the study:(1) On the study of hydrocarbon source rocks were analyzed respectively in the study of Neopaleozoic hydrocarbon source rocks and Paleozoic Majiagou group hydrocarbon source rock found in the study area is a mixed source for hydrocarbon(2) The reservoir in layers of rock types and sedimentary environment and reservoir petrophysical property and pore types of research, found that the study area mainly developed two types of reservoirs: the combination of weathering crust solution hole reservoir; another is combination of beach facies dolomite reservoir.(3) There are two types of cap rock in the study area. One is in Neopaleozoic of Benxi Formation at the bottom of the bauxitic mudstone caprock and Taiyuan Formation mudstone caprock is Ordovician weathering crust of the direct caprock; another is lower Paleozoic Ordovician Majiagou insider type cover layer, mainly including dense cap carbonate and evaporite seal layer as the use of local cover layer to reservoir.(4) A comprehensive analysis was carried out on the reservoir cap assemblage and trap types in the study area, and it was pointed out that the reservoir cap assemblage types were divided into the weathering crust of the ancient karst type reservoir cap and the assemblages reservoir cap. Besides, the type of trap is divided into a deeper level, the lithologic traps in the area are divided into the lens type lithologic traps and the upper inclined lithologic traps.(5) Through accumulation of comprehensive analysis on the area of natural gas to determine the area into a main controlling factors for good "source storage grooming and reservoir”. The model of the reservoir: mixed source for hydrocarbon(Neopaleozoic coal source rocks for hydrocarbon based), palaeohigh control reservoir, vertical to the carrier(unconformity surface, ancient groove) and lateral migration and long distance transport.