| The eastern margin of Ordos Basin is the area where coalbed methane was developed earlier in China with a history of more than 20 years.The Wu Bu mining area is a part of the Jin Xi flexural fold belt in Ordos Basin in terms of regional tectonic location.The overall strata strike near north and south,dip west,and the main body is monoclinal structural form.Coal are developed in Ben Xi formation of upper Carboniferous and Tai Yuan formation and Shan Xi formation of lower Permian.The extensive development of carboniferous-Permian coal measure strata,the material composition and sequence structure characteristics of coal measure strata determine the basic geological conditions for the formation of large and medium-sized coalbed methane fields in Wu Bu mining area.Drawing on the exploration experience of neighboring areas,the research is carried out by comprehensive methods such as data investigation,field exploration,experimental testing,numerical simulation and engineering analysis.The geological conditions of coalbed methane reservoir formation are analyzed,and the key scientific problems of coalbed methane sweet spot prediction are systematically studied.Based on the study of regional tectonic background and fault system,this paper clarified the sequence framework of the Upper Paleozoic and the composition of the late Paleozoic coal measure strata in Wu Bu mining area,analyzed the sedimentary evolution characteristics of the section containing coal,and made clear the basic resource conditions of the source rocks.Based on geological background and coal accumulation of source rock,controlled by the geological condition analysis of geological conditions of the coalbed methane,controlled by the five factors to complete the coalbed methane rich integrated geological conditions,it is divided into the rich integrated combination characteristic,and on this basis the prediction of complete CBM dessert area,combined with the innovation of downhole laser Raman test method complete CBM dessert area evaluation.The main achievements and conclusions are as follows:(1)The regional structures represented by the Western Shan Xi flexural fold belt and the Wu Bu Fu Gu fault belt have laid the foundation for later structural gas control of coalbed methane,and the regional sediment-uplift characteristics have laid the foundation for large-scale coal formation and coalbed methane reservoir formation.(2)Clarify Wu Bu mining area on the late Paleozoic carboniferous Ben Xi group,Tai Yuan group of lower Permian,the Shan Xi group of lower Permian stratigraphic sequence and composition,and the sequence stratigraphy of the basic unit,to identify regional unconformity surface and weathering crust,tectonic regime transition surface,under the surface of discontinuity of sedimentary facies,channel section and scour surface,condensation of the regional distribution and flooding surfaces such as the the sea floor.(3)The sedimentary characteristics of the main sedimentary microfacies of the Upper Paleozoic in Wu Bu and its adjacent areas are summarized,and the coal seam and its overlying and underlying sedimentary horizon are discussed in detail.The Middle Permian Shi Hezi formation and the Upper Permian Shi Qianfeng formation are mainly lacustrine and fluvial facies.The Lower Permian Shan Xi formation and lower Shi Hezi formation are delta facies.Ben Xi formation of upper Carboniferous and Tai Yuan formation of Lower Permian are shore facies,lagoon facies and shallow Marine facies.(4)Coal formation and distribution of hydrocarbon source rock is controlled by sedimentary,characterized by wide regional distribution of coal seam,the sedimentary facies in vertical and horizontal orderly combination control structure,namely the sedimentary facies and space combination directly controlled the formation and distribution of CBM reservoir,combination advantage of sedimentary facies is the necessary condition to control the gas reservoir formation.(5)Coalbed methane reservoir formation is controlled by resource conditions,gas bearing capacity,recoverable capacity,reservoir structure and hydrogeology.The coalbed methane reservoir controlled by multiple factors is divided into two types of reservoir formation combinations:inner source type and near source type.The coalbed methane in the source coalbed methane reservoir shows dynamic transformation of adsorption state and free state within and between layers.The free gas and adsorbed gas in the near source coalbed methane reservoir will be connected with the overlying sandstone for escape migration through the dredging channel,and they belong to the same origin and co-generation with the adjacent sandstone gas,and they are always in the dynamic transformation,migration and accumulation dynamic equilibrium state.(6)The resource conditions of the upper Paleozoic coal measure source rocks in Wu Bu mining area are comprehensively evaluated,and it is believed that the Wu Bu mining area has the basic geological conditions for forming large and medium-sized coalbed methane fields.The predicted coalbed methane resources are 167.33×10~8m~3,and the reserve abundance is 1.80×10~8m~3/km~2.(7)The prediction model of coalbed methane sweet spot was established by mathematical method,and three sweet spot spots were delineated in T1 coal seam of Ben Xi formation and S1 coal seam of Shan Xi formation.And through the innovation of downhole laser Raman validation test method of coalbed methane content,combined with forecast and verify the test results for dessert area forming condition analysis,the geological conditions of the coalbed methane study serve dessert area prediction,using dessert area evaluation and dessert area formation analysis roots forming geological conditions,complete the closed-loop research. |
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