Hydrocarbon Generation Characteristics Of The Lower Paleozoic Organic-rich Shale In Northern Daba Mountain

The discovery of the Fuling shale gas field in western Chongqing and the Weirong shale gas field in southern Sichuan marked a breakthrough in the exploration of the Lower Paleozoic dark shale in the Sichuan Basin.The geological survey and evaluation of the Lower Paleozoic shale gas in the periphery of the basin,including the North Daba Mountain,has also received attention.Drilling results on the southern margin of the North Daba Mountain found that the mass volume of the shale in the Lower Cambrian Lujiaping Formation was 0.045m3/t-24 m3/t.At the same time,the geological survey also found oil seedlings and bitumen spots in the area,indicating that the Lower Paleozoic of the Northern Daba Mountain has oil and gas potential.Therefore,it is urgent to study the hydrocarbon generation characteristics of organic-rich shale in the Lower Paleozoic Lujiaping Formation and Banjiuguan Formation in the North Daba Mountain.The results of the study will be used for the exploration and deployment of shale gas in the basin margin area including the North Daba Mountain.It is of great significance.This thesis is guided by source rock evaluation and oil and gas accumulation theory.Based on the full investigation of previous research results,X-ray diffraction,kerogen microscopic component analysis,organic carbon content test,and saturated and andaromatic hydrocarbon mass spectrometry-chromatography are analyzed.In-depth study of the organic matter abundance,types and sources of organic matter,and organic matter maturity of organic-rich shale in the Lujiaping Formation and Banjiuguan Formation in the North Dabashan area,based on this,combined with the mineralogy characteristics of rock samples,storage space characteristics and structural preservation conditions predict possible shale gas accumulation modes and favorable prospects for shale gas exploration.The paper mainly draws the following conclusions:(1)The TOC values of organic shale samples in the Lower Cambrian Lujiaping Formation are between 0.182%-9.063%with the average value of 3.21%which belongs to good source rock;The TOC values of 43 samples of organic shale in the Lower Silurian Banjiuguan Formation are between 0.038%-2.941%with the average value is 0.691%which belongs to poor source rocks.However,31.25%of the samples TOC more than 1%which belong to medium source rocks.(2)The organic matter micro-components of the Paleozoic organic shale samples in the Northern Daba Mountain contain a high proportion of saprophytic mud and crustal groups.The TI value of the Lujiaping Formation is 51,75-77,75,and the organic matter type is ?;the TI value of the Banjiuguan Formation is 59-85.5,and the organic matter type is mainly ?-?type.The biomarker combination analysis of saturated hydrocarbons and aromatic hydrocarbons shows that the organic matter parent materials of the two groups of samples are mainly derived from marine low-grade organisms,with medium-high salinity in the reduction deposition environment.(3)The Ro and Tmax values of the Lower Paleozoic Lujiaping Formation in the North Daba Mountain are 1.36%-2.56%and 418?-530? with the average of 1.863%and 460 ?;The Ro and Tmax values the Banjiuguan Formation are 1.47%-2.12%and 381?-539?,with the average of 1.773%and 483.5?.Both groups of shale samples entered the stage of high maturity to too mature.(4)The average content of brittle minerals in the Lujiaping Formation of Northern Daba Mountain is 84.57%and the average content of clay minerals is 10.54%;the average content of clay minerals in the Banjiuguan Formation is 47.5%,and the average content of brittle minerals is 50.37%.The content of medium and high brittle minerals and the development of a large number of micropores and mineral matrix pores of the two sets of samples indicate that they have the potential to form free gas reservoirs.The high content of clay minerals in the Banjiuguan Formation indicates that this group also has the potential to form adsorption gas reservoirs.potential.(5)Comprehensive consideration of the dark mudstone thickness distribution and structural conditions,it can be selected as a shale gas remote scenic spot in Maoba Town to Taoyuan area and Huangu Town to Shuangpingzi area in Ziyang County with relatively gentle topography,relatively slow strata.