Reservoir Characteristics And Main Controlling Factors Of The Lower Member Of Shahejie Formation In The Central Part Of Shulu Sag

As the great breakthrough of tight oil exploration in Huabei Oilfield, rudstone and marlstone tight reservoir in the 3rd Member of Shahejie Formation of Shulu Sag in southern Jizhong Depression has been paid more and more attention. The reservoir characteristics and main control factors are analyzed thoroughly with large amounts of data, including X ray diffraction, core observation, rock slices identification, SEM, stable isotope, capillary pressure data, petrophysical data, as well as interpretation of well logs. On this basis, we summarizes a set of reservoir classification standard, and made a comprehensive classification and assessment accordingly.The types of sedimentary facies were mainly lake facies, subaqueous fans and fan-shaped delta. According to the lithologic association, sedimentary structure sedimentation rhythm, rock fabric characteristics and electrical characteristics, we summarized eight sedimentary microfacies. Then, the sedimentary facies pattern was made to explain the causes of reservoir body:conglomerate and sandstone are the main cause of mixed sedimentation but laminated marlstone is the main cause of autochthonous sedimentation. However, massive marlstone has two genesis mechanism:mixed sedimentation and autochthonous sedimentation.The lithology of reservoir is particular:it is carbonatite in mineral composition, but it has typical structural features of clastic rocks. So, in this paper, we analyzed characteristics of clastic component and matrix component in detail, combined with structural characteristics, and summed up the nine kinds of rock types. By means of the casting thin sections and scanning electron microscope, we found that the reservoir space of target layer is mainly micropore and micro fractures. Physical property test results show that the reservoir in the lower part of the 3rd member of Shahejie Formation in the central of Shulu Sag is tight reservoir generally. The pore throat structure of reservoir can be divided in three types by analyzing the capillary pressure curve morphology and distribution of pore throat:fine pore medium throat structure, fine pore fine throat structure and fine pore micro throat structure.Through studying four characters of reservoir, we establishment the lithology, oil gas identification graph and the mathematical formulas between interval acoustic transit time and porosity, which provisde important evidence for reservoir classification and evaluation. By setting up the mathematical model with isotope, we get the paleotemperature and buried depth of the calcite in fractures. And then, the period of fractures was determined according to the burial history map. The results show that the fractures in target layer mainly formed in the 1th Member of Shahejie and 2nd Member of Dongying. Besides, the forming period of fractures is earlier than the expelling hydrocarbon period, which indicates that the fractures were effectiveness as hydrocarbon pore volume or migration path. Diagenesis in of target layer is various, including compaction, cementation, dissolution, metasomatism, and filling and transformation of clay mineral. Then, this thesis summarizes the characteristics of diagenetic sequence and pore evolution characteristics based on rock structure, authigenic mineral and pores types and distribution.Influenced by sedimentary microfacies, mineral components, lithofacies type, fracture, organic matter, diagenes, etc, the physical property of reservoir presents a certain regularity with those control factors. The effects of sedimentary microfacies show that the reservoir in interbedded mixed deposition and braided channel have better physical property. In addition, dolomite had evident effects on reservoir physical property:the higher content of dolomite, the better of the reservoir physical. For the lithofacies type, there also exist some effect on reservoir properties. The reservoir properties of laminated marlstone and clast-supported terrigenous rudstones are the best. Furthermore, abundant organic matter and lots of fractures are also benefit the properties. Pore evolution shows that diagenesis also has a controlling effect on reservoir properties. Compaction, late cementation and filling and transformation of clay minerals and advanced cementation on reservoir had a devastating effect. Conversely, early cementation and dissolution were helpful.On the basis of reservoir space type, porosity, electrical characteristic, permeability and pore throat structure, this paper create a set of standards for the classification of the target layer in the study area. According to it, the reservoir in target layer is divided into ?,?, ? types. Finally, the control factors of high quality reservoir are analyzed synthetically and we concluded that the zone is rich of organic matter and fractures is the priority area in hydrocarbon exploration and development.