Reservoir-Quality Evaluation Of Chang 6 Oil Accumulation And Geology Research On Enlarging Boundary In Jingan Oilfield

The article mainly analyzes the chang 6 reservoir in the upper Triassic in Ordos Basin. By tectonics, sequence stratigraphy, sedimentology and diagenesis, poly-statistics, and so on. It touches many professional fields, composing of 7 chapters and 23 sections.After analyzing of the whole situation, granularity is smaller. The lithology of chang 6 oil-bearing is a set of felspar sandstone. Little of them are rock-scraps felspar sandstone. According to the analysis of petrology, we find that Chang 6 oil-bearing is consisted with middle size sandstone and fine sub-sand. Chang 6 sandstone belongs to system of lacustrine deltas and mostly influenced by river. From evolution of sedimentary, chang 6 sandstones is a process of growing, development, fast development and shrinkage term. Among them, chang 621 and 612 sandstone is in fast development period, forming many oil-gas gatherings. Due to study area lie in the front part of deltas, so the factors of sedimentology are simple. According to analysis of sedimentology, we think the most benefit environment to reservoir is under-water branch and river mouth bars microfacies, which often form thick sand bodies of high porosity of permeability. They are skeletal sand bodies in system of delta and places of most reservoir distribution. The diagenetic processes that govern reservoir properties include the extent of compaction, cementation and dissolution of grains. We recognize that at the early diagenesis phase, mechanical and chemical compaction is very strong, which reduced the original porosity. Cementation is an important factor to reservoir, including carbonate, clay and laumontite cementation, etc. Cementation filled the room among grains and jammed the path between grains are another factors making sandstone compacted and very low permeable. At the late diagenesis phase, the dissolution of frame grains, especially the dissolution of felspar and laumontite, is the key to form secondary porosity. They changed the porosity characteristics of sandstone, engendering new benefit storing beds consisted with secondary porosity. We can find that the dissolution of laumontite can improve the oil-bearing beds' lower porosity and permeability, which are the best places for oil and gas store. In a word, the diagenetic study of reservoir property show that mechanical compaction and cementation is two important diagenetic controlling-factors, which make oil-bearing physical property bad and porosity down in reservoir. Dissolution is one of most important diagenetic controlling-factors making oil-bearing physical property well and forming better reservoir. At last, we pose 5 rules to value reservoir and found a mathematics model by poly-statistics. After proposing the study wells by the model, we classify all reservoirs and predict new benefit places.