The Study On Sedimentary Organic Facies Of Permo-Carboniferous Coal And Associate Rocks In Dongpu Sag

Sedimentary organic racies or Carboniterous-Permian coal and associate rocks in Dongpu Sag are studied by way of the analysis of organic petrology and combining organic geochemical experiments with previous achievements.It is concluded that the potential of oil and gas generation is related to different sedimentary organic facies in the study area.The main conclusions are as follows:1.According to the analysis of organic petrology and organic geochemistry of coal-bearing rock series in different regions and layers in the Dongpu Sag,the hydrocarbon source rocks of Carboniferous-Permian coal-bearing rock series are mainly distributed in Taiyuan Formation and Shanxi Formation.The types of organic macerals are rich and the macerals is mainly vitrinite(vitrinite content>55%).In the vitrinite the rich fluorescent desmocollinite B is an important feature of the organic matter of the coal-bearing series in the study area.It is illustrated that the desmocollinite B is rich lipid components by Micro-FTIR.In Taiyuan Formation and Shanxi Formation,the content of hydrogen-rich components such as desmocollinite B,exinite and sapropelite in source rocks of Taiyuan Formation is higher than Shanxi Formation,and the type of organic matter in Taiyuan Formation is also better than Shanxi Formation,and the TOC、S1+S2、IH are all higher in Taiyuan Formation.But the content of inertinite group in Shanxi Formation is higher than in Taiyuan Formation,and the hydrocarbon generation potential of source rocks in Shanxi Formation is relatively low.The hydrogen-rich content in the Qingzuji area is significantly higher than other areas.The types of carbonaceous mudstone and coal rock organic matter are mainly Ⅱ2 and dark mudstone is mainly type Ⅲ with a few type Ⅱ2.Because of the high thermal evolution extent in the Machang area,the organic macerals is mainly the inertinite,leading to the low hydrocarbon generation potential.2.Based on the quantitative analysis of organic macerals、four-terminal element rule and organic geochemistry and sedimentary facies,coal-bearing rock series of the Carboniferous-Permian in Dongpu Sag are divided into six sedimentary organic facies:①dry inertinite humic organic face;②shallow water-covered vitrinite humic organic face;③water-covered exinite humic organic face;④water-covered containing sapropelite humic organic face;⑤deep water sapropelite humic organic face;⑥open lake sapropelite organic face.Dry inertinite humic organic face’s organic macerals are mainly rich inertinite and vitrinite with poor hydrogen-rich composition.The content of inertinite is generally>30%and mainly fusinite and inert debris,in the fusinite pyrofusinite is ofen found in some areas.Dry inertinite humic organic face is mainly distributed in the Machang area,IH<50mg/g·TOC,S1+S2<25mg/g;The macerals components of shallow water-covered vitrinite humic organic face are mainly vitrinite which content is more than 70%,the carbonaceous mudstone and coal rock contain lots of desmocollinite B.This face is widely distributed in Taiyuan and Shanxi Formation and also is the most widely distributed sedimentary organic face in Dongpu Sag,IH is between 50-150mg/g·TOC,S1+S2 is between 50～100mg/g;The macerals components of water-covered exinite humic organic face is characterized by high exinite content(>30%),exinite mostly are microsporinite and resinite which are distributed in desmocollinite B.This face has smaller distribution range,mainly distributed in the upper of Taiyuan Formation.IH is between 100-200mg/g·TOC,S1+S2 is between 50～150mg/g;The macerals components of water-covered containing sapropelite humic organic face are mainly hydrogen-rich components,the content of exinite is more than 20%,and the sapropelite is mainly bituminite formed by lower organisms or plants,its content is less than 10%.This face is mainly distributed in the Wenliu and Qingzuji areas.IH is between 150-200mg/g·TOC,S1+S2 is between 100～200mg/g;The content of exinite(>20%)and sapropelite(>10%)are higher in deep water sapropelite humic organic face,the exinite group are mainly cutinite and microsporinite,and the sapropelite are mainly alginite and bituminite.This face is less distributed in Dongpu sag,mainly distributed in parts of Qingzuji area.IH is between 200-250mg/g·TOC,and S1+S2 is 150～200mg/g;The macerals components of open lake sapropelite organic face is mainly characterized by alginite and bituminite,and hydrogen-rich content is mostly>30%.This face is only distributed in the carbonaceous mudstone of the Taiyuan Formation in well Qinggu-2 meanwhile the average hydrogen-rich content can reach 37.54%in well Qinggu-2,IH>250 mg/g·TOC,and S1+S2>200 mg/g.3.The sedimentary organic facies of the Carboniferous-Permian coal-bearing rock series in Dongpu Sag are mainly dominated by shallow water-covered vitrinite humic organic face and dry inertinite humic organic face,which accounts for about 70%of the total facies,and also contain a certain amount of hydrogen-rich organic facies which are mainly the water-covered containing sapropelite humic organic face(accounting for 16%)and the water-covered exinite humic face(accounting for 7.5%).On the one hand,the proportion of shallow water-covered vitrinite humic organic face and dry inertinite humic organic face of the Shanxi Formation are higher than that of the Taiyuan Formation,while the proportion of the hydrogen-rich organic facies is smaller than that of the Taiyuan Formation.On the other hand,the hydrogen-rich organic facies are very abundant in Qingzuji area,while the dry inertinite humic organic face is mainly distributed in Machang area.The results of hydrocarbon source rocks thermal simulation experiments show that shallow water-covered vitrinite humic organic face has high gas generation potentiality,and also generatesa few oil-because there is rich desmocollinite B;Dry inertinite humic organic face has the lowest potential of hydrocarbon generation potentiality that Only a small amount of gas could be generated;The hydrogen-rich organic facies not only have oil generation potentiality but also gas generation potentiality,and their typies of organic matter is equivalent to the hydrocarbon generation potentiality of the type Ⅱ1-Ⅱ2,and the type of hydrocarbon generation depends mainly on the organic maturity.Based on the analysis of the distribution and hydrocarbon generation potentiality of the organic faces of coal-bearing rock series in the Upper Paleozoic of the Dongpu Sag indicate that the hydrocarbon generation potentiality of coal-bearing rock series in the study area depends on the sedimentary organic facies.Hydrocarbon generation potential of Taiyuan Formation is higher than that of Shanxi Formation due to its richer hydrogen-rich organic facies.The highest hydrocarbon generation potential is in Qingzuji area of Dongpu Sag.