| The Dongying Depression is one of fault-sag lacustrine basins with enriched petroleum resources. During the last40-year petroleum exploration, the investigating targets became to potential oil pools reserved within lithological interfaces from the structural reservoirs. However, due to the difficulties for the petroleum prediction on this kind of oil-pools, it constrained these potential reservoirs’exploration and evaluation in the future. As for the complexities of oil-gas reserving process, the hydrocarbon migration is merely one step in its process of inorganic fluid from the argillaceous source rock to the reserving sandstone. The pore fluid resulted from the argillaceous source rock affected heavily on the reserving sandstone on its diagenesis of minerals, which could control partially its formation and assemblage essentially. This research targets a fluid effect in the argillaceous-sandstone source rock system based on the investigation of mineral diagenesis from the source rocks of Upper Unit in the fourth Member (ES43) and the Lower Unit in the third Member (ES3) of Shahejie Formation in Dongying Depression.The first, comparisons on the diagenetic mineral and bulk-rock geochemical features have been made from the core samples of Units ES43and ES31in Dongying Depression. The diagenetic carbonate minerals in Unit ES43developed characteristically with highly contents of high-Mg calcite and ferrous dolomite; its clay minerals enriched with chlorite, and abundant of pyrite as well, which indicate a depositing environment of salinity with enriched element sulfur. Whereas, the carbonate minerals in the Unit ES31contain mainly mineral calcite; and its clay include minerals of illite, illite-kaolinite mixture, and kaolinite with few of pyrite, which means an environmental condition with low concentrations of salinity and sulfur. Geochemical data reveal that the source rock of ES4shows relatively high concentrations in elements of Mg, Ca, Fe, Ba, Sr, and heavy isotopic compositions of carbon and oxygen as well. These could deduce that the diagenitic fluid expelled from the source rock of Unit ES43with the same geochemical characters.The second, this research analyzed the type of minerals, its assemblage and it spatial distribution of Unit ES31. The geochemical compositions of carbonate minerals in this Unit changed identifiably in different regions. The cement minerals contain mainly ferrodolomite with high content of element Sr near the fault Niu18-Niu20and southward nearby. In the northern side of Niu18-Niu20, it changed to be high content of ferroan calcite and calcite minerals with few of ferrodolomite; however, it developed merely in calcite in the eastern area of Dongying Depression. Significantly, the cemented clay-mineral composition displayed also changing distributions in different areas. In the Fault Niu18-Niu20and its southern side nearby, the cemented clay minerals are composited mainly of illite, kaolinite, chlorite, and chlorite-smectite mixture occasionally yielding with abundant minerals of chlorite and chlorite-smectite mixture elsewhere (e.g.,3244m depth in the Well N43); In the northern side of Fault Niu18-Niu20, it changes to be high content of illite and kaolinite minerals, but with sparse of chloritand chlorite-smectite; but it yielded merely the minerals of illite and kaolinite in the eastern area of Dongying Depression.The third, this research recognized two relationships involving in the synergistic diagenesis between argillaceous and sandstone rocks under analysis of diagenetic minerals in this area. In the sandstone reservoir in the Fault Niu18-Niu20and nearby, the sandstone cements containing mainly with the minerals of ferrodolomite, chlorite, and chlorite-smectite mixture are result of the salinity fluid input with enriched elements of Ca, Mg, and Fe, which excluded from the Unit ES43with similar geochemical compositions. Whereas, the sandstone cements in the northern side of Fault Niu18-Niu20, which enriched with ferroan calcite but without chlorite and chlorite-smectite mixture, reflect the influences from the diagenetic fluid input of source rock in Unit ES31. Meanwhile, the relatively high content of element Sr in this sandstone cement means that it is still under the fluid effects from the Unit ES43. In the eastern side of Dongying Depression, the sandstone cement characteristically with high mineral contains of calcite, kaolinite and illite was the results of diagenetic fluid input from the source rock of Unit ES31. These conclusions are consistent with the results from researches of source rocks in this area before.The fourth, this research discussed further the spatial relationships and its dynamic drive between the source rock and sandstone reservoir. The analysis on the inclusion textures in the sandstone cements reveals that high salinity and captured temperature occurred near the Fault Niu18-Niu20, which supported very well the evidence of high-pressure occurrence observed in this area before. This relative high pressure might be the driving force for the diagenetic fluid migration around. In the eastern side of the Dongying Depression, the analyses of sandstone inclusion texture found no evidence for the anomaly of high-pressure occurrence even from the exploration data before. We excluded that the driving force should migrated by the lateral system within rocks and by the channel connections in the fault belts. The migrating channel system of the diagenetic fluid varied by different connecting systems in this area. It generally transported by the pore system and/or the microlaminar system in normal pressure condition; however, it could migrate by the macro and/or micro-crack systems in the fault belt and rocks. The fault belt of Niu18-Niu20was a primary migrating channel for the diagenetic fluid transportation and release, which perfectly cut deeply downward through the source-rock beds of Unit ES31and ES34. Furthermore, this research observed also that abundant micro-crack system developed in the argillaceous source rock, which mostly filled by the sparry calcite; however, the remaining unfilled cracks should significantly to be connecting channel system for the diagenetic fluid migration. |
PDF Full Text Request