Study On The Quality Of Reserviors Of Yanchang Formation In Fuxian, North Shanxi Province

In Mesozoic in Fuxian, North Shanxi province, the sedimentary fades varied frequently, the reservoirs had involved distribution strong heterogeneity and poor physical quality, and the tectonic traps almost didn't exist. So, to find the property of rocks in which reservoirs formatted easier comparatively and the strata traps are the primary work to do.This paper begins with the diagenesis, pore structure and physical quality, and studies on the reservoirs systematically, evaluates the quality of them, and comes to forecasts combinated with the sedimentary studies earlier.1. The reservoirs of the Yanchang formation almost are fine feldspathic sandstone, feldspathic debris sandstone, rock fragment feldspathic sandstone, and little quartzose sandstone. The structural maturity of sandstones is middle to poor and the componential maturity is low.2. There are five types of diagenesis in the study area: compaction(mechanical compaction and chemical corrosion), politic cementation, calcareous cementation, siliceous cementation& feldspathic cementation and corrosion.3. The type of diagenesis is different in different strata, and the diagenetic differentiation of chang 8 member is the strongest.4. The diagenesis has gone through many stages. Compaction come the first, then all kinds of cementation take place, and corrosion end. The succession of cementation is also clear, the first is politic cementation, then siliceous cementation, and the last is calcareous cementation. And, the politic cementation exists during all the diagenetic stages with different occurrence. One is pore edged, and the other is pore filled.5. The organic thermal evolution indicates that R₀ of the Yanchang formation is between 0.51-1.26%. Chang 1 member to chang 6 member is mature period, chang 7 member to chang 8 member is mature-high mature period, and chang 9 member to chang 10 member is high mature period. Combinated with scanning electron microscope, thin sections and so on, this paper deduces that the Yanchang formation had ever come up to A-B stage of late-diagenesis.6. The main types of pore are corrosion pore between grains, residual pore between grains and corrosion pore in grains. The average diameter of pore is 53.47 μ m, the average throat width is 15.76 μ m, the average coordination number is 1.12, and the average ratio of pore and throat is 1.44.7. Based on the mercury testing and physical quality (porosity, infiltration rate) analysis, by the classification standard, chang 8 member belongs to fine pore tiny throat type (IV V type),chang 6 member belongs to small pore fine throat type and fine pore tiny throat type (III-IV type), and chang 2 member belongs to fine pore tiny throat type and tiny pore tiny throat type (III-IV type).8. This paper establishes the template of depth-porosity and depth-infiltration rate, and finds they are negative related. The correlation analysis of grain size and porosity in identical depth shows good positive relation. Comparison between different sedimentary facies of identical depth presents that distributary channel has best physical quality, cch and mouth bar is next to it, and cvs and sch is poorest.9. Among many factors affecting reserving capability, the dominating factors are diagenesis, sedimentation and tectonism.10. The main types of reservoirs in study area are delta-type and turbidite-type. And Chang 8 member and chang 6 member are potential good reservoirs.