Recent exploration results indicate that a significant exploration potential remains in the Dongying Depression of the Bohai Bay Basin and the undiscovered oil and gas are largely reservoired in subtle traps including...Recent exploration results indicate that a significant exploration potential remains in the Dongying Depression of the Bohai Bay Basin and the undiscovered oil and gas are largely reservoired in subtle traps including turbidite litholigcal traps of the Sha-3 Member. In order to effectively guide the exploration program targeting turbidites, this study will focus on the depositional models of the Sha-3 Member turbidites and oil/gas accumulation characteristics in these turbidites. Two corresponding relationships were found. One is that the East African Rift Valley provides a modern analog for the depositional systems in the Dongying Depression. The other is that the depositional models of line-sourced slope aprons, single point-source submarine fan and multiple source ramp turbidite, established for deep-sea turbidites, can be applied to interpret the depositional features of the turbidite fans of three different origins: slope turbidite aprons, lake floor turbidite fans and delta-fed turbidite fans in the Sha-3 Member. Updip sealing integrity is the key factor determining whether oil/gas accumulates or not in the slope aprons and lake floor fans. The factors controlling oil/gas migration and accumulation in the delta-fed turbidite fans are not very clear. Multiple factors rather than a single factor probably played significant roles in these processes.展开更多
The origin of dolomite in Shahejie Formation shale of Jiyang Depression in eastern China were studied by means of petrologic identification, compositional analysis by X-ray diffraction, stable carbon and oxygen isotop...The origin of dolomite in Shahejie Formation shale of Jiyang Depression in eastern China were studied by means of petrologic identification, compositional analysis by X-ray diffraction, stable carbon and oxygen isotopic composition, and trace element and rare earth element analyses. The results show that the development of dolomite is limited in the lacustrine organic rich shale of Shahejie Formation in the study area. Three kinds of dolomite minerals can be identified: primary dolomite(D1), penecontemporaneous dolomite(D2), and ankerite(Ak). D1 has the structure of primary spherical dolomite, high magnesium and high calcium, with order degree of 0.3-0.5, and is characterized by the intracrystalline corrosion and coexistence of secondary enlargement along the outer edge. D2 has the characteristics of secondary enlargement, order degree of 0.5-0.7, high magnesium, high calcium and containing a little iron and manganese elements. Ak is characterized by high order degree of 0.7-0.9, rhombic crystal, high magnesium, high calcium and high iron. The micritic calcite belongs to primary origin on the basis of the carbon and oxygen isotopic compositions and the fractionation characteristics of rare earth elements. According to the oxygen isotopic fractionation equation between paragenetic dolomite and calcite, it is calculated that the formation temperature of dolomite in the shale is between 36.76-45.83 ℃, belonging to lacustrine low-temperature dolomite. Based on the maturation and growth mechanism of primary and penecontemporaneous dolomite crystals, a dolomite diagenetic sequence and the dolomitization process are proposed, which is corresponding to the diagenetic environment of Shahejie Formation shale in the study area.展开更多
文摘Recent exploration results indicate that a significant exploration potential remains in the Dongying Depression of the Bohai Bay Basin and the undiscovered oil and gas are largely reservoired in subtle traps including turbidite litholigcal traps of the Sha-3 Member. In order to effectively guide the exploration program targeting turbidites, this study will focus on the depositional models of the Sha-3 Member turbidites and oil/gas accumulation characteristics in these turbidites. Two corresponding relationships were found. One is that the East African Rift Valley provides a modern analog for the depositional systems in the Dongying Depression. The other is that the depositional models of line-sourced slope aprons, single point-source submarine fan and multiple source ramp turbidite, established for deep-sea turbidites, can be applied to interpret the depositional features of the turbidite fans of three different origins: slope turbidite aprons, lake floor turbidite fans and delta-fed turbidite fans in the Sha-3 Member. Updip sealing integrity is the key factor determining whether oil/gas accumulates or not in the slope aprons and lake floor fans. The factors controlling oil/gas migration and accumulation in the delta-fed turbidite fans are not very clear. Multiple factors rather than a single factor probably played significant roles in these processes.
基金Supported by the National Natural Science Foundation of China(Grant Nos.42172153,41802172)Sinopec Key Laboratory Project(Grant No.KL21042)Shengli Oilfield Company Project(Grant No.YKS2101)。
文摘The origin of dolomite in Shahejie Formation shale of Jiyang Depression in eastern China were studied by means of petrologic identification, compositional analysis by X-ray diffraction, stable carbon and oxygen isotopic composition, and trace element and rare earth element analyses. The results show that the development of dolomite is limited in the lacustrine organic rich shale of Shahejie Formation in the study area. Three kinds of dolomite minerals can be identified: primary dolomite(D1), penecontemporaneous dolomite(D2), and ankerite(Ak). D1 has the structure of primary spherical dolomite, high magnesium and high calcium, with order degree of 0.3-0.5, and is characterized by the intracrystalline corrosion and coexistence of secondary enlargement along the outer edge. D2 has the characteristics of secondary enlargement, order degree of 0.5-0.7, high magnesium, high calcium and containing a little iron and manganese elements. Ak is characterized by high order degree of 0.7-0.9, rhombic crystal, high magnesium, high calcium and high iron. The micritic calcite belongs to primary origin on the basis of the carbon and oxygen isotopic compositions and the fractionation characteristics of rare earth elements. According to the oxygen isotopic fractionation equation between paragenetic dolomite and calcite, it is calculated that the formation temperature of dolomite in the shale is between 36.76-45.83 ℃, belonging to lacustrine low-temperature dolomite. Based on the maturation and growth mechanism of primary and penecontemporaneous dolomite crystals, a dolomite diagenetic sequence and the dolomitization process are proposed, which is corresponding to the diagenetic environment of Shahejie Formation shale in the study area.
