The Analysis Of Shale Gas Accumulation Conditions In The Upper Paleozoic Ordos Basin

Ordos Basin is located in the west of Huabei platform.Its basement rock is Archaeozoic and lower Proterozoic metamorphics.Ordos Basin is a multicyclic craton basin with simple structure and monolithic fluctuation and has abundant coal and oil and-gas.In order to evaluate the accumulation potential of shale gas in this area,Based on the analysis of observations and samplings of outcrops and cores,the text of geochemical parameters,physical parameters,chip identification,scanning electron microscope and X-ray diffraction.Using theories of sedimentology,geochemistry and unconventional geology,we probed into the accumulation conditions of organic-rich shale,such as sedimentary facies,thickness and distribution,organic matter type and content,and maturity and porosity.And then,accumulation potential of shale gas in C-P formation was predicted by the gas surveying.The finding shows that Ordos Basin Upper Paleozoic C-P shale is distributed in the swamp,delta,barrier island,lagoon and tidal flat.Swamp and delta phase is more important because the former contributes to the hydrocarbon generation and the latter provides an ideal depositional environment which is favorable to the carbonaceous shale and dark shale with thick layer.Marine-continental transitional organic-rich shale distributes widely in the Upper Paleozoic Ordos Basin.Their TOC is high,generally from 0.65 to 29.18%,with an average of more than 2.1%,organic matter type is mainly humic,and maturity is at the stage of massive gas generation which is from 1.0 to 3.0%.All these features help to generate shale gas.The average effective porosity of shale concentrates around 4%and permeability concentrates in the range of 0.01 to 1×10-3?m2,and it is belong to ultra-low porosity and ultra-low permeability reservoir.Marine-continental transitional organic-rich shale contains multiple types of pores and cracks,including dissolved pores,intergranular pores,expulsion residual pores in organic matter,etc.Moreover,cracks include diagenetic fractures and structural fractures.All in all,these pores and cracks are preparing not only for shale gas reservoir space but also for the shale gas output migration pathways.According to the comprehensive information,Summed up marine-continental transitional shale gas accumulation model in the Ordos Basin.Shanxi formation through Shenmu-Suide-Yanchang in the east,Taiyuan formation through Wushenqi-Hangjiqi-Dongsheng-Shenmu and Etuokeqi-Yanchi in the north,and Benxi formation through Jingbian-Hengshan-Yulin-Shenmu in the northeast are favorable areas of C-P marine-continental transitional shale gas resources in Ordos Basin.Preliminarily forecast that the Upper Paleozoic C-P shale gas geological resources of Shanxi formation are up to 2.1 trillion 11m3 and shale gas of Taiyuan formation geological resources are up to 3.2 trillion m3.