| The paper has studied on the reservoir petrography, diagenesis features of the Upper Es4 in Dongying depression and analyzed the heterogeneities of various features in different sedimentary facies zones and diagenetic evolution sequence using core, thin section, and analysis assay data combined with sedimentary facies and sand-body distribution. In the end, we acquired the following major awareness.The inner-fan of nearshore subaqueous fan and turbidite fan is composed of brecciafacies and conglomeratic sandstone facies; The mid-fan is mainly composed of conglomeratic sandstone facies, gravel-bearing sandstone facies and sandstone facies; The terminal fan is composed of sandstonefacies and mudstone facies. The study area is composed of feldspathic lithic sandstone and lithic arkose sandstone, and the rock constituents are similar in the eastern and western area.The sandstone of the Upper Es4 is characterized by crystallized rock, intermediate-acid magmatite, granitoid, limestone, dolomite, mudstone, gneiss. In the T121 wellblock of the eastern area, it is mainly composed of granitic gneiss and granite and metaquartzite, accompanied with fewer limestone. While in the T125 wellblock of the western area, it is composed of diate-acideffusive rock and metaquartzite; In the T127 wellblock, it is composed of limestone and dolomite accompanied with metaquartzite and fewer diate-acideffusive rock. In the T168 wellblock, it is composed of granitic gneiss and limestone with fewer diate-acidmagmatite.The reservoir of Upper Es4 in Shengtuo region is determined in the middle of diagenesis A stage and mid-diagenesis A1 in most area, a few in the middle diagenesis B stage. The reservoir has experienced the diagenetic environment with early alkaline—I-acid—late alkaline—II-acid from the shallower to the deeper. Carbonate cementation is extremely developed and characterized by heterogeneity. In the Upper Es4-cx,it has higher Carbonate cementation content than that in the Upper Es4-cs. Carbonate cementation is relative enriched in the the terminal fan and outer fan, which can reach 15-20%. In the mid-fan, it has a relative lower content, which is lower than 5%. In the Upper Es4-cs, it has a higher surface porosity than that in the Upper Es4-cx. The mid-fan has a higher siliceous cement content than the the terminal fansubphase.The sediments developed in main channel microfacies of middle fan subfacies in nearshore subaqueous fan have low content of calcium and matrix, and thus higher facial porosity, and the diagenetic evolution sequence shows features of early weak cementation and later strong dissolution. The sediments developed in middle fan subfacies of turbidite fan also have low content of calcium and matrix, however, the diagenetic evolution show features of early strong dissolution and later asphalt shrinkage with strong cementation. Sandstones with these two types of diagenetice volution sequence are most favorable for hydrocarbon accumulation. The glutenite bodies developed in near-foot middle fan subfacies, in spaces between channel of middle fan subfacies, and in rim fan subfacies have high content of matrix, and they show features of densification because of strong calcareous cementation and week dissolution.As oil-bearing grades come from high to low, the content of cementation becomes higher, such as intergranular space. In the meantime, the reduction of porosity due to compaction becomes lower while the reduction due to cementation becomes higher. These facts indicate that there is significant relationship between cementation and oil-bearing condition. Based on the amount of interstitial material, the glutenites can be divided into four kinds: strong dissolution oil-rich glutenite, strong compaction with distorted plastic clasts oil-free glutenite, and strong calcareous cementation oil-free glutenite. The first kind has relatively higher intergranular porosity volume. |
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