Gas derived from the primary cracking of kerogen and the secondary cracking of oil has historically been the focus of petroleum geologists,given its importance as a gas source.The Wenchang A Depression within the Zhu ...Gas derived from the primary cracking of kerogen and the secondary cracking of oil has historically been the focus of petroleum geologists,given its importance as a gas source.The Wenchang A Depression within the Zhu Ⅲ Sub-basin is the largest gaseous hydrocarbon-rich depression in the Pearl River Mouth Basin(PRMB),and the sources of gaseous hydrocarbons in this depression are a research focus.Mudstones from the Eocene Wenchang Formation contain type Ⅰ and type Ⅱ organic matter and are oilprone,with TOC,S1+S2,and HI values mostly ranging from 1.42%to 3.12%,9.71 mg/g to 20.61 mg/g,and 410.71 mg/g TOC to 736.17 mg/g TOC,respectively.Data of gaseous hydrocarbon yields and carbon isotopic compositions show that the gaseous hydrocarbons generated from oil-prone mudstones are mainly derived from the secondary cracking of oil,and the plot of δ^(13)C_(2)-δ^(13)C_(3) versus ln(C_(2)/C_(3))effectively identified the gas source.To further assess the gas generation processes and the ratio of oil-cracking gas under geological conditions,we reconstructed the history of gaseous hydrocarbon generation in mudstones from the Wenchang Formation in the Wenchang A Depression.Results showed that gaseous hydrocarbon generation began at approximately 33 Ma,a maximum of 69%of total gaseous hydrocarbons(C_(1)-C_(5))was generated by oil cracking,and total heavy hydrocarbon gases(C_(2)-C_(5))were mainly generated from oil cracking(65%-81%).This study provides a deeper understanding of the characteristics of gas generated from oil-prone mudstones and is important for gas exploration in the Wenchang Depression.展开更多
Organic matter(OM)and minerals are major particle components of lacustrine shales.The influence of OM and minerals on pore space and structure in organic-rich oil-prone shales containing a large range of total organic...Organic matter(OM)and minerals are major particle components of lacustrine shales.The influence of OM and minerals on pore space and structure in organic-rich oil-prone shales containing a large range of total organic carbon(TOC)contents is poorly understood.In this study,we investigated the variation in pore space and structure of low mature lacustrine shales in the Songliao Basin(NE China),based on a study of the mineralogy,petrography,geochemistry,and geophysical properties of shales.Different pore types make markedly different contributions to the mineral surface area(MSA)and pore volume(PV)of the shales.There exists a negative correlation between MSA/PV and TOC in mesopores(r^(2)=0.75/0.65)and macropores(r^(2)=0.74/0.68),and a positive correlation in micropores(r^(2)=0.59/0.64),which are associated with the variation of mineral and TOC contents.A positive relationship between the throat/pore ratio and TOC(r^(2)=0.82)shows an increase in throat radius and decrease in pore radius with increasing TOC content.This relationship is supported by the reduction in mean pore diameter(MPD)for large pores and increase in MPD for small pores.These variations are related to the decreased pores by quartz plus feldspar(Q+F)content,increased throats by clay minerals,an d enhanced pore-fill by OM.We propose that the variation of OM and minerals is a key control on the pore space and structure of low mature organic-rich oil-prone shales.展开更多
基金supported by the Central Young College Teachers Fund Project of China(Grant No.3142020002)the Fundamental Research Funds for the Central Universities(Grant No.3142021004)+1 种基金the National Natural Science Foundation of China(Grant No.41673066 and No.42202291)the Construction of the Water Damage Model in the Xishan Coal Power Mining Area(Grant No.20230767).
文摘Gas derived from the primary cracking of kerogen and the secondary cracking of oil has historically been the focus of petroleum geologists,given its importance as a gas source.The Wenchang A Depression within the Zhu Ⅲ Sub-basin is the largest gaseous hydrocarbon-rich depression in the Pearl River Mouth Basin(PRMB),and the sources of gaseous hydrocarbons in this depression are a research focus.Mudstones from the Eocene Wenchang Formation contain type Ⅰ and type Ⅱ organic matter and are oilprone,with TOC,S1+S2,and HI values mostly ranging from 1.42%to 3.12%,9.71 mg/g to 20.61 mg/g,and 410.71 mg/g TOC to 736.17 mg/g TOC,respectively.Data of gaseous hydrocarbon yields and carbon isotopic compositions show that the gaseous hydrocarbons generated from oil-prone mudstones are mainly derived from the secondary cracking of oil,and the plot of δ^(13)C_(2)-δ^(13)C_(3) versus ln(C_(2)/C_(3))effectively identified the gas source.To further assess the gas generation processes and the ratio of oil-cracking gas under geological conditions,we reconstructed the history of gaseous hydrocarbon generation in mudstones from the Wenchang Formation in the Wenchang A Depression.Results showed that gaseous hydrocarbon generation began at approximately 33 Ma,a maximum of 69%of total gaseous hydrocarbons(C_(1)-C_(5))was generated by oil cracking,and total heavy hydrocarbon gases(C_(2)-C_(5))were mainly generated from oil cracking(65%-81%).This study provides a deeper understanding of the characteristics of gas generated from oil-prone mudstones and is important for gas exploration in the Wenchang Depression.
基金supported by the National Natural Science Foundation of China(Grant Nos.41772114,41402123)the CGS Research Fund of China(Grant Nos.J1901-33,J1803)the China Geological Survey(Grant No.DD20221817).
文摘Organic matter(OM)and minerals are major particle components of lacustrine shales.The influence of OM and minerals on pore space and structure in organic-rich oil-prone shales containing a large range of total organic carbon(TOC)contents is poorly understood.In this study,we investigated the variation in pore space and structure of low mature lacustrine shales in the Songliao Basin(NE China),based on a study of the mineralogy,petrography,geochemistry,and geophysical properties of shales.Different pore types make markedly different contributions to the mineral surface area(MSA)and pore volume(PV)of the shales.There exists a negative correlation between MSA/PV and TOC in mesopores(r^(2)=0.75/0.65)and macropores(r^(2)=0.74/0.68),and a positive correlation in micropores(r^(2)=0.59/0.64),which are associated with the variation of mineral and TOC contents.A positive relationship between the throat/pore ratio and TOC(r^(2)=0.82)shows an increase in throat radius and decrease in pore radius with increasing TOC content.This relationship is supported by the reduction in mean pore diameter(MPD)for large pores and increase in MPD for small pores.These variations are related to the decreased pores by quartz plus feldspar(Q+F)content,increased throats by clay minerals,an d enhanced pore-fill by OM.We propose that the variation of OM and minerals is a key control on the pore space and structure of low mature organic-rich oil-prone shales.
