Research On Geological Conditions Of Multi-energy Resources Enriched And Accumulation Systems In The Ordos Basin

The Ordos basin is featured by abundant multi-mineral resources, e.g. coal, oil/gas,uranium energy and others. However, it is still unknown for the formation of abundantmulti-type mineral resources in the same basin. Here we studied the aggregation conditionof four-kind minerals (e.g. coal, oil, gas, and uranium ore) showing different geologicalfeatures, proposed their mechanisms of the accumulation or mineralization, defined threetypes of the accumulation system, for example, Mesozoic oil/gas reservoir, Paleozoic deepbasin gas and Mesozoic uranium, and proposed their accumulation models. Thus somegreat progress was made in this study as follows.(1) Different types and different geological histories of depositional systems control themineral type distribution respectively. Paleozoic coal and coal seam gas in the whole basinis controlled by the regressive-low swamping; central oil and peripheral coal in Mesozoicis controlled by the north-south delta system development and to the central lake graduallyshranking; relatives coarse ore-controlling results in uranium distribution mainly on theedge of the basin.(2) Fluid potential studies on Triassic Chang6,7section have shown that the fluidpotential overall in the Early Cretaceous taking Jingbian-Wuqi-Qingyang line as theboundary; Late Cretaceous fluid potential significant reduction in Northeast Jingbian.Transition region formed at the end of the Triassic tight reservoir reservoir exploration anddiscovery are mainly distributed in the Early Cretaceous high potential to low potentialareas. So it verify the reliability of the fluid potential indicating the direction ofhydrocarbon migration and accumulation.(3) This study suggested the variation of the13C1isotope in Paleozoic reservoir revealsthe fractionation of the C isotope in the hydrocarbon expulsion and oil/gas migration ofPaleozoic source rocks, resulting in the decrease of δ13C1from the hydrocarbon-generatingcenter to margin. Therefore the decrease direction of δ13C1indicates the hydrocarbonmigration direction in the tight sandstone reservoir.(4) Based on the detailed analysis, the pressure-depth relationship controlled by capillaryforce in deep basin gas reservoir was proposed, displaying the pressure variation from thehydrostatic table to the interface of transition of gas-to-water and the pure gas reservoir,coinciding with pressure testing in the gas reservoir of Paleozoic deep basin in Ordos basin,which interprets the formation of the deep-basin gas reservoir.