Sedimentary and Reservoir Characteristics of Early Paleozoic in the Southern North China
|School||China University of Petroleum|
|Keywords||North China Southern Lower Paleozoic Carbonate Lithofacies pale geography reservoir|
Based on the theory of litho-stratigraphy and biostratigraphy, using regional stratigraphic section and well data, the southern North China’s reunification of Paleozoic strata correlation is realized, thus the Lower Paleozoic stratigraphic correlation framework is established. Based on the summary of spatial distribution of the Paleozoic strata, using clastic lithology statistical methods judge carbonate sedimentary environment, the early Paleozoic carbonate platform depositional environment is restored.The Lower Paleozoic strata in southern North China are mainly carbonate platform deposits in the shallow water. Main carbonate rock types are micrite, argillaceous limestone, oolitic limestone, biostatic limestone and dolomite, dolarenite, argillaceous dolomite. While, in some areas stromatolite and wormkalk are developed. Other rock types such as silicalite, shale and glutenite also can be seen. Common sedimentary structures are horizontal bedding, wavy bedding, parallel bedding, birds eye structures and stromatolite structure, ect. Development of six major types of sedimentary facies: tidal flat, restricted platform, open platform, shore shallow, shallow platform, shallow water and other types.The main evolution is: clastic littoral environment - mixed product ramp-type carbonate platform - the gentle slope of carbonate platform. The first time the earliest cambrian transgression reached the area south-east, near the ancient land area Luliang clastic tidal flat deposits, the second phase of the cambrian and turned the area mainly carbonate rocks. Late cambrian, there was a slight uplift of the crust, the sea level dropped, which caused extensive tidal flat deposits, in the central region missing upper cambrian strata, Into the Ordovician, the southern margin of the ancient continental uplift Xionger Variety, missing in southern lower ordovician strata, the western part of the Ordos very low and landing, but no debris deposition. Majiagou occurred the second large-scale transgression, to start a water carbonate rocks, rock single, southern margin of the tank connected with the Qinling. Pingliang, eastern crustal uplift, the sea retreated, forming the north land, only in the western border of this area, there Pingliang Sea, shows gravity flow deposition. The main types of reservoir porosity are fracture and dissolution pores. The main factors that affect the carbonate reservoir capability are litho logical characteristics and filling cementation, compaction and pressure solution, dolomitization, and dissolution diagenesis and tectonic stress, among which tectonic stress and diagenetic dissolution are the decisive factors for the final appearance of the reservoir.Lower Paleozoic carbonate reservoir types can divided into four types: karst reservoir; and recrystallization related dolomite reservoir; and structural related fractured reservoir; grain stone reservoir. The most important type is karst reservoir, the following are dolomite reservoir and fractured reservoir, while, grain stone reservoir is not that good. In the vertical aspect, the most favorable reservoir is in the Ordovician carbonate rocks, the following in the Cambrian dolomite. While, the Middle Cambrian Zhangxia group reservoir is not that good, reservoirs in other strata are worse. The weathering crust reservoirs formation in this area are caused by Supergene stage karst and porous dolomite reservoirs are controlled by litho logy. The combination of dolomite reservoirs and ancient karst reservoir at well Taican3 and its western areas, as well as Longxian at the southwestern margin of the Ordos and Liquan are better, which are favorable reservoir development area.