Characteristics Of Organic Matter Shale Deposit And Reservoir In The Lower Cambrian Niutitang Formation,Northeastern Chongqing

The Lower Cambrian Niutitang Formation in the northeastern part of Chongqing has good shale gas resource and great exploration potential.Based on the methods of field investigation and samping,drilling core observation,seismic data measurement and test analysis,the black organic shale deposits and reservoir characteristics of Niutitang Formation in Lower Cambrian were studied.The following results and knowledge have been obtained:1.The strata development characteristics of the Lower Cambrian Niutitang Formation in the northeastern part of Chongqing was clarified.Niutitang Formation is mainly distributed in Chengkou-Wuxi area.The lithology is mainly about gray black-black carbonaceous shale.The thickness of it varies greatly from 100 m to 600 m.The overlying strata is Mingxinsi Formation and the underlay strata is Dengying Formation.2.The sedimentary environment of organic shale in the Lower Cambrian Niutitang Formation of northeastern Chongqing was identified.The sedimentary environment of Niuyutang Formation is mainly continental shelf environment.From bottom to top,the environment changed from the deep water shed to the shallow water shed.Longitudinal,lithology from the bottom up in order to carbonaceous shale,siliceous shale,carbon and silty shale interbedded and silty shale.Horizontal,the strata in this place reflect as high strata of northwest and low strata of southeast.The water from northwest to southeast is gradually deepened,the environment changed from shallow water shed to deep water shed.3.The reservoir capability of organic shale in Niutitang Formation of the study area was analyzed.The black-rich organic shale in the Niutitang Formation is mainly concentrated in the lower section of the group.The content of brittle minerals in the black shale section is high,which is rich in brittle minerals,mainly quartz,feldspar and pyrite.Its content accounts for 41% 75% of the debris mineral content.The main pore types are intragranular pore,intergranular pore,fissure,organic pore,intercrystalline pore and interlayer pore of clay minerals.The average porosity is 2.42% and the distribution range is between 1.18% and 3.24%.Permeability is low,distributed in?0.0001⁰.01?×10^-3?m².The fracture development zone has a high value of permeability and the correlation between porosity and permeability is poor.4.The shale gas favorable development area of Niuotang Formation in the study area was divided.The type of organic matter contained in the black rich organic shale of Niuyutang Formation is mainly type I.The organic matter belongs to the over mature stage?general Ro> 2%?.The thickness is mainly distributed between 40¹20m.According to the latest shale gas evaluation standards,based on the analysis of the organic shale thickness,organic matter abundance,organic matter maturity and mineral composition and other aspects.Two lower Cambrian Niutitang Formation shale gas favorable area was selected,which are: Mingtong-Gaoguan area,Longtai-Zhongliang area.