Research On Reservoir Micro-characteristic Of Yanchang Formation In Fuxian Exploration Area Of The Ordos Basin

Applied with outcrop observation, core description, geophysical logging interpretation, thin section determination, Scanning Electron Microscope, reservoir lithology and physical property analysis and other analytic machinery, the sedimentary facies and micro-characteristic of Yanchang Formation in Fuxian exploration area are studied deeply.Viewpoint and method of high resolution sequence stratigraphy are firstly applied in Fuxian exploration area, Yanchang Formation are divided four scale Cycles, such as one Long-long-term Sea Level Cycle , four Long-term Sea Level Cycles, nine Middle-term Sea Level Cycles, and twenty-four Short-term Sea Level Cycles, and are compared with traditional stratum partition. By the studying of the paleocurrent direction and the light and heavy minerals, it make sure that NE is the main direction of sediment provenance, the original rock are Wulashan group in uper Archeozoic and down Proterozoic Erdaowa group in Daqinshan region north of Ordos Basin. Subaqueous distributary channel in delta front microfacies and subaerial distributary channel in delta plain microfacies are identified ,which are the main reservoir sand bodies for oil and gas of Yanchang Formation in Fuxian exploration area, the distribution of sand bodies distributed from northeast to southwest are dominated by sedimentary facies .Feldspar-lithic fine-sandstone and feldspar fine-sandstone are mainly sandstone of Yanchang Formation in Fuxian exploration area, the content of matrix is low and the content of cement is high which are mainly calcite ,chlorite films, in the second place are hydromica , autogeny-quartz , autogeny-feldspar, reticulation clay, Kaolinite and laumontite etc. All the sandstones have entered A period of late diagenetic stage. The dominant diagenesis types in the area are compaction, cementation, replacement and dissolution, in which compaction and cementation are mainly factors to reduce sandstone physical property and dissolution effectively improved physical property. Chlorite films cementation facies, mud cementation facies, feldspar and quartz cementation facies, carbonate cementation facies and laumontite solution facies are the main diagenetic facies . The area with chlorite film cementation facies and laumontite solution facies possess better physical property and with carbonate cementation facies possess bad physical property that forming compact belts.Remnant intergranular porosity , intergranular dissolution porosity, intragrnular dissolution porosity, filling constituents dissolution porosity, authigenic mineral intercrystal porosity are main pore types. Pore texture can be classified as following: small pore and fine throat type, small pore and micro-fine throat type, small pore and tiny throat type, tiny fine pore and micro-fine throat type and tiny fine pore and microthroat type. Yanchang Formation is low-pore and low-permeability reservoir and heterogeneity of sandy reservoir is very serious, as a whole, Chang2 and Chang3 is the best, Chang6 and chang8 is the second and Chang7 is the worst. In Fuxian exploration area, all sorts of reservoir sensitivity are below medium, by which production are not influenced seriously, even permeability become higher after acidification by hydrochloric acid, resulting in physical property improved. Therefore, acidification can be an effective measure of exploitation in this area.Reservoir are mainly influenced by sedimentary facies, tectonics and diagenesis. The control function of sedimentary facies for reservoir shows that sandstone is fine, such plastic grains as feldspar and lithoclast content are high, determining the original physical property of sandstone is not good. The feeble multiphase tectonic activity and low heat flow value are determined by the background of steady craton sedimentary basin , which results the reservoir experienced longer and stronger compaction and cementation, later hydrocarbon maturation, feebler organic acid dissolution and undeveloped fissure. All these facters decide that the characteristic of the reservoir in this area is low- pore and low- permeability.Studying the parameter of pore and permeability comprehensively and consulting prevenient study results of evaluation of reservoir, the reservoir is classified four types and the classification and distribution of reservoir in oii-bearing beds of Yanchang Fonnation are studied respectively.By looking for sand body and higher pore and higher permeability area, combined with oil product characteristic and electromotive curve data, eleven advantageous blocks of oil are predicted of different oibearing beds of Yanchang Fonnation in Fuxian exploration area, which provide the credibility geology gist for further exploration and exploitation in this area.