The Research Of Reservoir Characteristics Of Upper Triassic Xujiahe Formation In The Northeast Area Of Sichuan Basin

Based on the theory of Sedimentology and Reservoir Geology, a large number of relevant literature, the wild outcrop observation data and relevant indoor analysis test data, we systematically discuss reservoir characteristics and diagenesis of Xujiahe Formation of Upper Triassic in the northeast Sichuan Basin. And we finally expound various controlling factors of reservoirs and establish the reservoir formation and evolution mode.There are five reservoir rock types, including lithic quartz sandstone, feldspar lithic sandstone, carbonate lithic snastone, silicon lithic sandstone and glutenite. The composition maturity of lithic quartz sandstone is medium low or medium high, the structure maturity of lithic quartz sandstone is high or medium high; The composition maturity of feldspar lithic sandstone is low, the structure maturity of feldspar lithic sandstone is medium; The composition maturity of carbonate lithic snastone is low, the structure maturity of carbonate lithic snastone is medium high; The composition maturity of silicon lithic sandstone is low, the structure maturity of silicon lithic sandstone is low. The feature of clastic components is rich debris and poor feldspar, interstitial content is mostly carbonate, siliceous and clay minerals, and rock debris is mainly siliceous debris, carbonate debris and variable quartz sandstone debris.According to reservoir transformation effect, we divide diagenesis type into two types of destructive and constructive. Destructive diagenesis are compaction effect, pressure dissolve function, siliceous cementation, carbonate cementation and hole tacking filling role. Constructive diagenesis are ring edge chlorite cementation, altered function, dissolition, water action, table generating rock function and rupture role. Through a lot of core observation, chip appraisal, scanning electron microscope and X-ray diffraction, we divide various diagenesis facies. And Mud-siliceous-kaolinite diagenesis facies, mud-ring edge chlorite-illite diagenesis facies are the best. Mud-siliceous- calcite diagenesis facies, siliceous cementation diagenesis facies, calcium cementation diagenesis facies and real crush diagenesis facies are the worst.Reservoir of Xujiahe formation is mainly distributed in two sections of the second member and the fourth member of Xujiahe Formation. The feature of reservoir is low permeability and low porosity. Porosity distribution is 0.61-6.88%, average is 2.46%, main distribution interval is 0-4%. Permeability distribution is 0.0012-26.0086×10^-3μm²,average is 0.2944×10^-3μm²,main distribution interval is 0.01-0.1×10^-3μm². Reservoir type mainly belongs to porous-fracture type. According to the cause, reservoir space type is divided into remaining primary grained pore, secondary pore, hole and crack. And secondary pore can be divided into grained dissolution pore, grained microporous pore, in-grain dissolution pore, in-grain microporous pore, molding pore and oversized dissolution pore. The reservoir type of this area is mostly remaining primary grained pore, in-grain dissolution pore, in-grain microporous pore, molding pore and oversized dissolution pore, which is more for small microporous, low faces rate.This paper summarizes two important controlling factors of physical properties of the reservoir: sedimentation and diagenesis. Sedimentation of reservoir essentially effects reservoir rock type and structure component features. The type and intensity of latter rock diagenesis is controlled by the characteristics of rock. Diagenesis effects the evolution and pore throat structure characteristics of reservoir space. And diagenesis ultimately determines the stand or fall of physical properties and the distribution of the present reservoir.Through the previous research achievements and extensive testing analyzing data, we believe diagenetic stage is in high evolution level, overall in B period of middle diagenesis-C period of late diagenesis. Denudation in the late period of early diagenetic and early period of middle diagenetic, cataclasis in the late period of middle diagenetic play a important role in reservoir improvement.