| On the basis of previous researches about the sedimentaryframework,through the analysis of The main sedimentary rock types andmicro-structural,the Author think that the overall study area is in theopen platform facies with Weaker hydrodynamic conditions and lack ofhigh-energy deposition. The Sedimentary facies can be further dividedbioclastic beach and intraplatform depression Asia (micro) phase.Thebioclastic beaches belong to the low-energy beach. The main diagenesisinclude micritization, submarine cementation, compactiona anddissolution,hydrothermal, tectonic disruption, in which the mostimportant Diagenesis to the formation of reservoir is hydrothermal.Beforehydrothermal activity, the rocks experienced diagenesis which mainly todestroy the pore and lack of favorable hydrothermal fluid migrationsecondary porosity generation. According to the classification and statistics of the middle Permiandolomite micro-structural features found that the dolomite in the studyarea lack of fabric-preserving textures, and characterized by coarsernon-planar anhedral to euhedral saddle-like dolomite crystals. Besides,the dolomitization of the rock was not complete, with development of alarge number of transitional rock types. In addition, the rock extensivelydeveloped irregular hydrothermal dolomite-breaking cracks, sheet geode,zebra-like structure dolomite and hydrothermal special rock fabric. Again,dolomite holes and cracks can also be found hydrothermal activity relatedto quartz, illite, fluorite, pyrite, barite, bitumen and other hydrothermalminerals. When the rock was completely dolomitized, the dolomite wasmassive output, with the waning of the dolomitization degree, dolomitewas output with lenticular, leopard porphyritic. At the same time,thecloser distance to fault or more intense tectonic activity, the higher thedegree of dolomitization.Dolomite are mainly located in the theLongmenshan ancient fault zone, and Emei–washan mountain fault nearzonal.The homogenization temperature range of dolomite exceeds thenormal temperature corresponding maximum depth of the Stratum,indicating that the dolomite was hydrothermal product. The δ13C value ofthe dolomite is similar with the δ13C value of the micrite,means thedolomitization fluid was normal sea water or other high-salinity fluid, moreover, lack of fresh water effect. In addition, the δ18O value of thedolomite was partialnegative.Crossplots of fluid-inclusionhomogenization temperature(Th) against oxygen isotopic signature formatrixreplaciveand void-filling saddle dolomite from outcrop of dolomiteshow that dolomite formed from water enriched to strongly enriched inδ18O compared with the estimated isotopic composition ofcontemporaneous seawater, this relationship is typical of hydrothermalsystems.Multiple samples within the dolomite is significantly enriched inradioactive strontium, indicates that the hydrothermal fluids was from thebasement.Again, Although diabase intrusives and basalt REE was bigdifference, but the distribution model has a certain similarity, whichimply the source of the hydrothermal have a contact with basalt volcanicactivity. According to the distribution characteristics of the hydrothermalsedimentary deposits and hydrothermal sedimentary siliceous rock stratain southern China, and the paleo-heat flow evolution inversion results ofSichuan Basin, the Author think that the middle Permian dolomiteemplacement was very soon after deposition of the host, Specifically,atthe end of the Middle Permian to late the early Permian, whichcorrespond to the intensified rifting activity and deep magma activitiesCaused by Emei taphrogenesis.The middle Permian reservoir space main include intergranular holes,intergranular dissolution pores, caverns, the hydrothermal breaking cracks. Reservoir types including cracks-dissolution vug dolomite reservoir,Cloud limestone crack-shaped reservoir, which cracks-dissolution vugdolomite reservoir was better. Contrast hydrothermal dolomite andunalteratified limestone macro-structure and physical analysis, found thatHydrothermal activity was critical to reservoir performance. Thehydrothermal fundamentally changed the rock structure, produced a seriesof dissolved pores, so as to constitute a high-quality dolomite reservoir.The limestone is a general lack of effective reservoir space without thehydrothermal transformation. The same time, the hydrothermaltransformation have some negative impact on the reservoir, due to theholes was varying degrees filled with the minerals precipitatded from thehydrothermal process. |
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