Reservoir Characteristics Of Changxing Formation Of Permian In Xuanhan, Northeast Sichuan

Based on previous studies, and combined with the palaeontological characteristic,tectonics data, observation of outcrops and drilling data etc, understandingsedimentary framework features of Changxing formation in Xuanhan area. It isknown that the sedimentary framework of Changxing formation take on “twoplatform-one trough-one continental shelf”.On the basis of sedimentary framework knowledge, using the principle andmethods of sequence stratigraphy, by the analysis of the observation outcrops, drillprofiles and logs characteristic, Changxing formation in Xuanhan area is divided intotwo third-order sequences; according to the cyclicity characteristics of rock types andlogs cyclicity features, Changxing formation in Xuanhan area is divided into seven oreight fourth-order sequences, sixteen or eighteen fifth-order sequences. Furthermore,framework of third-order sequence and high frequency sequence are established.According to facies index of petrological characteristics, the biologycombination, tectonics and well-logging etc, we classify carbonate sedimentary faciesof Changxing formation in the Xuanhan area. Combining with the sequencestratigraphic study, the relationship between sedimentary facies, sea-level changes andsequence system tract and the development and the evolution disciplinarian of thesedimentary facies and microfacies in the study area are recognized.By means of modern analytical technology of rock and mineral, combining withresearch of petrological characteristics and geochemistry characteristics, it is knownChangxing formation in Xuanhan area developed many kinds of diagenesis, such ascementation, dolomitization, compaction and pressure-solution, dissolution,tectonization and hydrothermalism. The dolomitization played an important role informing high quality reservoir formation, and dissolution is the key factor of thereservoir formation. The study area mainly develop four types of dolomite:dolomicrite, powder–medium crystalline anhedral dolomite, powder–mediumcrystalline idiotopic dolomite and hydatothermal dolomite.Respectively follow the evaporative pumping dolomitization mode, seepage refluxing dolomitization mode,burial dolomitization mode and hydrothermal dolomitization mode. The Changxingformation of study area mainly developed three stage’s dissolution, includingsyngenetic-atmospheric dissolution, mid-eogenetic dissolution and late-diageneticdissolution.According to outcrops and examination of thin-section of the study area,combined with well-loggings, the reservoir rock types, reservoir types, reservoir spacetype of the Changxing formation are summaried and recognized.Based On the core,logging and logging trace and logging tace identification marks of reservoir, the singlewell profile’s reservoir of Changxing formation is dissected. Combining with researchof sequence stratigraphy and sedimentary facies, it is known that the reservoir mainlydevelops in the highstand system tract of third-order sequence, and the transgressivesystem tract of the upper third-order sequence rarely develops. The reservoir developsin the middle-upper part of third-order sequence totally, but it is not limited to this,also found in the lower-middle part of third-order sequence. The reservoir mainlydevelops in the edge of platform, and major develop in biohermal facies, beach facies,tidal flat facies.By the analysis data of drilling core porosity and permeability, reservoirparameters are analysised by well-logging, it is revealed that reservoir physicalproperty of different sedimentary facies types exist differences, including the bestreservoir physical properties is biohermal facies, reservoir physical property of tidalflat facies and beach facies take second place. But, generally, the Changxingformation reservoir main developsⅡ and Ⅲclass in the study area.