Reservoir Forming Conditions And Characteristics Of Coal Measure Tight Sandstone Gas In Kangning Area In East Margin Of Ordos Basin,China

The coal measure tight sandstone gas is rich in Kangning area in east margin of Ordos basin,the exploration area is broad,the geological factors are variable and the gas pool forming process is complex.Based on the dynamic changes of geological conditions in the process of coal measure tight sandstone gas accumulation,the paper mainly studies the sedimentary evolution process of coal-bearing gas reservoirs,coal-bearing source rocks and coal reservoir characteristics,and the physical property distribution law of multi-layer tight sandstone reservoirs,the control effect of sedimentary microfacies and reservoir physical properties on gas reservoirs,and the source-reservoir relationship of the sedimentary-diagenetic-tectonic comprehensive effect.And the characteristics of the enrichment and depositional model of the coal measure tight sandstone gas in the eastern margin are systematically dissected.This paper describes the evolution sequence of the marine-marine continental transitional-continental sedimentary environment in the tight sandstone reservoir,and the sedimentary evolution model under different phase control conditions is established.The tight sandstone of Taiyuan Formation is mainly formed in marine sedimentary microfacies of barrier bars,tidal channel,tidal sand dam and sand flat.The tight sandstone of Shanxi Formation is mainly formed in marine-continental transitional sedimentary microfacies of the distributary channel,the underwater distributary channel and mouthbars.The tight sandstone of the lower-upper Shihezi Formation is mainly formed in continental distributary channels,underwater distributary channels and mouthbars.The tight sandstone of the Shiqianfeng Formation is mainly formed in mid-channel bar microfacies and retention sediment of the braided river.The developmental characteristics of coal-bearing source rocks and coal reservoirs are systematically evaluated.And the potential and contribution of coalbed and shale to hydrocarbon generation are discussed.The abundance of organic matter in three sets of mudstone is mainly concentrated in the range of 1%-4%,and the hydrocarbon generation potential is moderate-excellent grade.Mudstone kerogen is mainlyⅡ₂,Ⅲtype,that is,organic matter type is mainly sapropelic-humic type and humic type,biased towards gas type.The hydrocarbon generation potential of the coal seam is obviously larger than that of the mudstone,and the hydrocarbon generation potential of the carbonaceous mudstone and the dark mudstone is similar.Based on the analysis of the physical properties of several sets of tight sandstone reservoirs,the reservoir classification and evaluation criteria were established.Through a large number of experimental data,the comprehensive studies of reservoir petrological characteristics,pore type characteristics,pore structure characteristics and physical properties,the optimal reservoir evaluation standard is established.Three types of dominant reservoirs were identified based on petrology,physical properties,pore structure,pore type,capillary pressure curve,sedimentary microfacies and productivity situation.The control effects of sedimentary microfacies and reservoir physical properties on the gas layer are explained in detail.Five kinds of sand body gas-bearing modes were put forward,that is gas-bearing in the box cycle,in the top of funnel-shaped cycle top,in the middle of compound cycle,in the bottom of bell-shaped cycle and in the internal of compound cycle.And then established a"micro-phase control reservoir,physical control possession"of the dense sandstone accumulation mechanism.The effects of sedimentary-diagenetic-tectonic on the coal source reservoir cap assemblage,reservoir physical properties and enrichment rules are summarized.Source-reservoir combination is divided into three types:source reservoir cover combination,near source reservoir cover combination and far source reservoir cover combination.And this paper presents a reservoir enrichment and accumulation coupling mode of"physical properties control possession in the source-physical properties and structure control possession of near source-structure control possession of far source"in the study area,which plays a direct role in exploration and development work.