Research On The Organic Geochemistry Of Black Shale In HuNan SangZhi Region

Taking the Niutitang formation shale of lower Cambrian system and the Longmaxi formation shale of lower Silurian in SangZhi block in northwest of Hunan as the research object,the paper gets the following conclusions.1.SangZhi block locates in the southeast of Sichuan-west of Hunan and Hubei.Its geotectonic background is in the central Yangzte plate,a superimposed structure with different structures interacted with each other.Structure in Sangzhi is relatively simple,which extend to Northwest of the "S".The formation in the study area presents that the northern rocks is older than the southern rocks.The target layer series Niutitang and Longmaxi black shales' TOC is higher than other shale layers,and their thickness and continuity also are better.the types of sedimentary facies in Niutitang formation are continental shelf and slope facies.and the type of sedimentary facies in Longmaxi formation is continental shelf2.The type of kerogen in the study area mainly is ? kerogen,followed by ?-? mixed kerogen and ? sapropelic and humic kerogen.The TOC of Niutitang formation is more than 3%.In the plane,TOC is gradually increased from southwest to northeast.In the section,TOC is decreased from the bottom up because the anaerobic environment was destroyed.The TOC of Longmaxi formation is about 3%.In the plane,TOC is gradually increased from south to north.In the section,TOC is decreased from the bottom up because the anaerobic environment was destroyed.The averaged Ro in Niutitang formation is 3.6%.In the plane,it shows an increasing trend from southwest to northeast.It is in the high mature to over mature stage,which is net gas stage.The averaged Ro in Longmaxi formation is 2.68%.In the plane,it shows an increasing trend from southwest to northeast.It is in the high mature to over mature stage,which is net gas stage.3.With analysis of organic geochemical column,the paper consider the black shales of Niutitang and Longmaxi formation in Sangzhi are better source rock.Based on the relation between Toc and S1/w(TOC),chloroform bitumen "A"/w(TOC),the paper conclude the lower limit of organic carbon content in Sangzhi area is about 0.5%.4.The averaged Langmuir volume of the black shale in Niutitang formation is 2.24m~3/t,and the averaged Langmuir pressure is 2.14MPa.In the plane,it shows an increasing trend from southwest to northeast.In the northeast of the study area,the adsorbed gas content is 2m~3/t.The averaged Langmuir volume of the black shale in Longmaxi formation is 1.13m~3/t,and the averaged Langmuir pressure is 3.22MPa.In the plane,it shows an increasing trend from southeast to northwest.In the northwest of the study area,the adsorbed gas content is over 1.8m~3/t.5.The main factors affecting the adsorption capacity of Paleozoic shale in Sangzhi include internal and external factors.Internal factors are TOC and clay minerals content.External factors are pressure,temperature,and moisture.