The Reservoir Diagenesis And Microscopic Characteristics Research Of Putaohua Oil Layer In The Region Of Talaha-Changjiaweizi

The main part of Talaha-Changjiaweizi region is located on the middle of Qijia-Gulong Depression which is the second structure unit of Songliao basin,the area is about 1663 km2, the target of this research is Putaohua Oil Layer, which is a part of the First Member of the Yaojia formation of Upper Crataceous. The lithologies in this area mainly consist of gray, celadon mudstone, gray silty mudstone, pelitic siltstone, siltstone. Putaohua oil layer has a good regional cap rock, a good oil source rock of Qingshankou Formation.Putaohua Oil Layer equipped rich oil and gas, and has a good foreground of exploration, which was preliminary forcasted that estimated petroleum reserves will be over a hundred million ton. But, because of the interbed of thin sandstone and thin mudstone, it is imprecise to identify the layer using seismic data, which makes lithology and sedimentary facis of reservoir indefinite, and therefore the study of properties and influence factor of reservoir has an effect to the further exploration and exploitation.On the basis of detail surveying regional geological background and petroleum geological condictions of study area, by methods of the following combined studies including core observation, thin-section analysis, granularity analysis and so on. Three sedimentary facies including delta, lacustrine and lacustrine bottom are recognized, and more seven sedimentary subfacies and thirteen sedimentary microfacied. The main reservoir sand types are distributary channel under water sedimentary sand, estuary dam sedimentary sand, sheet sand sedimentary sand, braided channel sedimentary sand and turbidite sedimentary sand.Using the methods such as thin-section identify, casting thin-section observation, scanning electron microscopy, cathodeluminescence microscopic analysis, describing reservoir characteristic of Putaohua Oil Layer subtly. The studied area's sandstone is mainly composed with feldspathic litharenite and litharenite. The interstitial materials are mainly clay minerals and carbonate cement. Compositional maturity and texture maturity of the rock is lower. The diagenesis reservoir sandstone mainly underwent comprise compaction, pressolution, cementation, metasomatism, corrosion,dissolution and clay minerals transformation. The common clay minerals in this area are illite, chlorites, kaolinite , illite and smectite mixed lays. The clay minerals transformation is mainly in the second rapid stage.The reservoir was in the A2 sub-stages of mid-diagenesis period,The diagenetic sequence of cement and authigenic mineral was glauconite, pyrite, crystallite calcite,adhesion calcite,secondary quartz,illite, chlorites, albitization, cement filling calcite, ankerite.diagenetic fluids experience early alkaline fluid stage, acid fluid stage and return to late alkaline fluid stage.And Glauconite, pyrite, crystallite calcite, some quartze corrosion and adhesion calcite were the diagenetic sequence in alkaline environment in early age; The incursion of oil and gas made the pore fluid acidic, corrosion of feldspars was coming, kaolinite and secondary enlargement of quartze was generated; The dissolution of carbonates and feldspars, adding to the smectite transformation, the concentration of basic ion was increasing,which made the pore fluid alkaline, The precipitation of calcite and dolomite, albitization was generated,the partial dissolution of some quartze grain even authigenic quartz were appeared.At the depth of 1600-2100 meters, as a result of maturation of organic matter,a great deal of acidic fluid had been generated,diagenesis environment was kept in acidity,the corrosion , dissolution of feldspars and calcite, intergranular dissolution porosity and intragranular dissolution porosity came into being, the secondary pore zone was generated. Below 2100 meters, due to the corrosion , dissolution of feldspars and calcite,a great deal of basic ion, uch as Fe2+, Mg2+ ,K+ had been dissociated out, react with kaolinite to generate lots of chlorites. the content of kaolinite had been cut down, but the content of chlorites had been added to about 40%, they had a relationship of restricting each other; At the same time, due to the conversion of Smectite to illite,the content of illite was increased gradually, clay minerals during transformation caused physical property of the reservoir bad. With the increasing of the buried depth, the arenite of the reservoir had been cementated again, the late carbonates filled the early dissolution pores, which caused the reservoir porosity depressed, secondary enlargement of feldspar was very common;Due to the great buried depth and the compaction,some mineral grain came apart at the seams.There are eight pore types in Putaohua Oil Layer reservior which are common intergranule pore, narrowing intergranule pore, erosion enlarge intergranule pore, erosion pore in the interstitial filling materials, erosion intragranular pore, casting erosion pore, fracture pore, and pore among clay minerial. Thereinto, erosion enlarge intergranule pore(70%) and erosion intragranular pore(20%)give a priority to the pore. The types of throat mainly include shrinking part of variable fracture and flaky or bend flaky throat, sometimes tubal throat can be seen. The average of throat diametral is 0.218-3.577μm, and throat can be divided into the following two types under the standard, thin throat and imperceptible throat. It is mainly made up of imperceptible throat. By studying the capillary pressure curve, analyse the reservoirs rock's microscopic pore structure quantitatively and qualitatively, it is confirmed that pore throat radius disperse more widely, permeability is better, and the bigger pore throat make a main contribution towards permeability. Porosity and permeability are interrelated, and microscopic pore structure determine the permeability rate.By means of core displacement test, combined with permeability ratio curve characteristic and analysed, anhydrous displacement efficiency average value is 27.23%; When water content 98%, recovery ratio is 35.53% in average; The final recovery ratio is only 39.83% in average.It shows that, in this area, recovery ratio is lower, and the water/oil displacement characteristics is worse.On the basis of above studies, we discuss the main factors which influent reservoir characteristics. Two important factors give the control to the reservoir, which are sedimentation and diagenesis. On sedimentary, material composition, granularity size, matrix content and sedimentary sandstone types control the reservoir properties. The beneficial reservoir is such a reservoir which is high in arkose and clastic, wide in granularity, low in matrix content, distributaries channel under water sandstone and braided channel sedimentary sandstone. On diagenesis, compaction, agglutination, meta-somatism, dissolution.is a main control action for to reservoir properties. Dissolution can alter reservoir; otherwise, compaction and agglutination destroy the reservoir. So, the beneficial reservoir is short of compactation and agglutination and good development in dissolution. The affecting factors for reservoir vadose characteristics contain microscopic pore structure and reservoir sensitivity.By means of large number of real and basic geological documents and core analysis and testing data, the microscopic and macroscopic characteristics of the reservoirs have been researched in detail, thus it has provided basic geological evidence for advantageous target region optimization, the above studied results possess much more important theoretical significance and practical value for forther exploration and exploitation.