Study On Sandstone Pathway System Of Middle & Lower Permian In Northeastern Ordos Basin

Migration and accumulation was controlled by dynamic condition and pathway. It was a hotspot that how to confirm the distribution of pathway within the dynamic of hydrocarbon accumulation.Sandstone bed on fluvial channel and delta front was the main pathway system of Permian in northeast Ordos basin. Integrated study on the sedimentary system and diagenesis, the sandstone pathway system was investigated. First, on study of sedimentary system, orientation of palaeo-current, characteristics of well-logging, the sedimentary facies was confirmed. Secondly, on basis of rate of sandstone in bed, thickness of sandstone, the distribution of sandstone body was mapped. By investigating of phenomenon of diagenesis, period of diagenesis was delimited, characteristics of diagenesis was described. And then, diagenesis sequence and development of porosity were rebuilt. Finally, integrated of pathway of sandstone bed and hydrocarbon dynamic system, the characteristics of hydrocarbon migration were analyzed.It indicated that debris material of Shanxi formation mainly derived from precambrian metamorphic rock on the north part of Ordos basin. The distribution of sedimentary system was controlled by two water systems. Alluvial fan, fluvial and delta were three mainly sedimentary systems in Shan'xi and lower Shihezi formation. Delta system was the domination sedimentary system on investigation. Sedimentary facies have extent from east to west, and they were distribution from north to south along fluvial channel respectively. The distribution of sandstone body was affect by the situation of fluvial channel, and it became thinner and finer gradually from north to south.The diagenesis of Permian sandstone was violence. Compaction, squeeze, and cementation were mainly types of diagenesis, which made the porosity of sandstone degradation severely. However, corrosion and crystal of kaolinite improved the condition of porosity. Otherwise, fracturing and jointing from tectonic activity had the same function.Study on diagenesis sequence shown that compaction was occur on phase of early diagenesis, and porosity degraded about 60%. Cementation of clay mineral was occur on the B phase of early diagenesis, and 5%~8% porosity degraded. Secondary enlargement of quartz took place from B phase of early diagenesis to B phase of later diagenesis, it made 1.9%~2.8% porosity vanished. Corroded crystal of feldspar and clastic debris by acid water made secondary porosity during the A phase of early diagenesis. At the same time, authigenes kaolinite was deposition. Corroded crystal of kaolinite is an important type of porous in Shan'xi formation.The key moment of pool-forming was early Cretaceous. Integrated study of distribution of sedimentary facies and diagenesis sequence, high porous belt was located from Jingbian to Yulin region in early Cretaceous. Result of development of porosity of Shan'xi formation indicated that the 2nd member was average 8%, and 7.3% in the 1st member. Integrated condition of porous and distribution of sandstone body, the most prospective region of porosity-sandstone pathway was located at north of Jingbian, south and northeastern ofHengshan and Mizhi reigion.