Sequence Stratigraphy, Sedimentary Facies And Reservoir Characteristics Of Shiniulan Formation In Southeast Area Of Sichuan Basin

This thesis focuses on the Shiniulan formation carbonate reservoir in the Southeast Area of Sichuan Basin, under the guidance of the Carbonate Sequence Stratigraphy, Reservoir Sedimentology, Reservoir Geology, and by means of the combined methods of indoor & outdoor and macroscopy & microscopy, stratigraphic sequence, sedimentary facies, diagenesis and reservoir characteristics of Shiniulan Formation are studied emphatically. As a result, the characteristics of stratigraphic sequence and sedimentary facies in Shiniulan Formation are found out, and the main diagenesis, its effect on reservoir and reservoir characteristics are made clear.Firstly, identification on key sequence boundaries of each outcrop and drilling core is presented at first, to classify sequence stratigraphy; then, on the basis of sequence stratigraphic classification of all outcrops and drilling cores, the characteristics of sequences and tracts are analyzed; at last, the Shiniulan Formation sequence stratigraphic framework is established, so contrast of sequences and tracts cross platform-shelf is also achieved. The Shiniulan Formation in the Southeast area of Sichuan Basin is divided into four 3rd-order sequences, each sequence includes transgressive systems tract and high systems tract.Secondly, based on the data of drilling cores, outcrops and microsection, and by establishing the sedimentary facies columnar section of typical sections, sedimentary facies of the objective interval are analyzed; depositional model is also established; then, sedimentary facies types and characteristics are confirmed; at last, using tract as basic unit, the distribution of different sedimentary facies throughout different periods is mapped. The main sedimentary facies types include restricted platform facies, open platform facies, shoal facies of platform margin, platform ramp facies and continental shelf facies. The distribution and development rule of Shiniulan shoal patch is analyzed. The Shiniulan shoal patch develops in two places, the platform margin and the internal platform. The platform margin shoal develops in the high system tract of the upper 3rd-order sequences, and it transforms from progradation to retrogradation due to the eustatic sea level change and carbonate production rate.Thirdly, on the basis of sedimentary facies, combining the methods of petrology and geochemistry with a large number of microsection data, both pattern and characteristics of the main diagenesis are illustrated in detail and their effect on reservoir is analyzed; and then, both diagenetic sequence and stages are also classified. The conclusions as follow: The Shiniulan reservoir experiences relatively simple diagenetic evolution in its burial history,intense compaction and cementation have destructed almost all primary pores and part secondary pores. As a result, Shiniulan carbonate rock in the studied area becomes a kind of tight reservoir. The reservoir capacity in Shiniulan Formation decreases a lot after four diagenetic stages including syndiagenetic stage, eogenetic stage, postdiagenetic stage and tectonic stage.Lastly, based on the data of microsection, porosity, permeability and mercury penetration, the reservoir interval,reservoir spaces,physical property and pore configuration are analyzed; then, the types of reservoir are also verified. The lithological types of reservoir in Shiniulan formation are diverse, including marlite, knollenkalk, microcrystalline limestone, grain micrite and dolomite. The main reservoir spaces of Shiniulan carbonate rock are cracks, corrosion pores along the cracks and intergranular dissolution pores, but they are all filled by bitumen now. Generally, the Shiniulan reservoir is characterized to be tight with low matrix porosity, the average is 1.58%, and about 73% of which belows 1%; above 50% of the sample permeability belows 0.2 millidarcy. The large pores generated previously are mostly filled by organic matter and calcite, left some micropore only. So the physical property of Shiniulan carbonate is very poor, and it only develops some fractured reservoir.