Research On The Relationship Between Abnormal Pressure And Gas Accumulation In Upper Paleozoic Of Northen Ordos Basin

The abnormal pressure in Petroliferous basin is an universal important geological phenomenon. It is indicated through more and more studies that abnormal overpressure had close relation with hydrocarbon migration and accumulation, which is paid much more attention by geologists. Aiming at the characteristics of universal low abnormal pressure, tight reservoirs, simple tectonics, dispersed gassy beds, complicated mechanism of gas accumulation in upper Paleozoic of Ordos Basin, the distribution pattern of formation pressure in the areas of Tabamiao, Hangjinqi, Sugelimiao and Yulin area etc. is analyzed through the research of pressure data from more than 200 wells in the areas, the rule of hydrocarbon pooling in the compartments is also analyzed, and hydrocarbon migration-accumulation and pooling models are established.Main cognitions and research results are as follows:(1) through quantitative calculation of pressure and synthetical analyse It is indicate through quantitative calculation of pressure and synthetical analyse that: â‘ under-compaction is the main factor of high pressure on non-source rocks in the compartments at present; â‘¡hydrocarbon generation is the main factor forming ancient high pressure in the source rocks; â‘¢hydrothermal condition has dualism; â‘£geotemperature falling in tectonic uplift-denudation and the later period and sandstone "springback" are the main factors resulting ancient high pressure dropping in the reservoirs.At present, the pressure compartment is a coexistence system of alternate high and low pressure in upper Paleozoic. It is discovered through the research that there is a better regularity between the acoustic wave traveltime, electrical resistivity of the sandstone and burial depth. The segmentations vertically reflect that different stages, such as the normal, the constructive and destructive diagenesis periods. Pressure compartment protected effectively the development of secondary porosity in the sandstones. At the time of hydrocarbon pooling process, acidic water is very favorable to the development of secondary porosity in the sandstones in the pressure compartment.(2) Three key phases of pressure and hydrocarbon pooling are put forward through the detailed analysis about sedimentary burial history, hydrocarbon-generating history, diagenesis history, geothermal history and combining with the synthetic analysis on compacting characteristic of the sandstone and mudstone, reconstruction history of pressure origin and evolution, inclusion analysis, denuded thickness et. al. The importance of tectonic uplift to gas pooling in upper...