The Formation And The Distribution Of Lower-middle Ordovician Carbonate Reservoir In Eastern Tarim Basin Region

On the understanding of the lower-middle ordovician sedimentary pattern of Tangdongregion and the observation of rock core and cuttings to realize that the main types of rocks aremicrite, grain limesttone, algal boundstone, marl, mudstone, limy dolomite and dolomiticlimestone, dolomite, etc. According to the development of reservoir space in all kinds of rocks,reservoir space is summarized into three categories: Pores, holes and cracks. Combined withthe cause of reservoir space, which is divided into beach facies limestone dissolution poretype reservoir, limestone karst seam hole type reservoir, solution pore dolomite reservoirs anddolomite karst seam pore-cave reservoirs, and logging response characteristics of varioustypes of reservoir is established. While knowing the study of contribution characteristics instatistical analysis of the porosity and permeability of the rock in that area, at the same time,by using the measured porosity data, the logging data and the methods of linear regression,the general physical properties of reservoir was studied.As the formation of carbonate rock reservoir influenced by diagenesis, which was studiedin the mid-lower ordovician strata in the area. And according to the different influence ofdiagenesis on reservoir, the diagenesis are divided into two categories:1) playingconstructive role to the reservoir including dolomitization, dissolution, tectonic fracture effect,etc.;2) damage to the reservoirs including compaction, pressolution, cementation effect and itsmineral (such as pyrite, quartz), dissolved pore, cave and packing action of vacuole andfracture. Because of the complexity and its positive role on reservoir formation, thedolomitization and dissolution are focused on.According to dolomite crystal size, crystal morphology, crystal surface features,orthogonal polarizer light dissipation characteristics, cathode rays luminance, carbon andoxygen stable isotopes, rare earth and trace elements, X diffraction degree of order,thedolomite because of various composition can be divided into Syngenetic evaporation of thecause of pump powder-microcrystalline dolomite, syngenetic penetration reflux causespowder-mesocrystalline it dirty dolomite, shallow bury the powder-mesocrystalline causesthe euhedral dolomite, hydrothermal transformation genesis of coarse grain dolomite,hydrothermal genesis saddle dolomite. Phase syngenetic dolomitization into shallow burialdolomitization is a continuous process. From Syngenetic phase formation of dolomite toshallow buried under the conditions of formation of the dolomite, the oxygen isotopic is gradually reduced, the values and degree distribution gradually increased, Mn content ishigher and higher, but patterns of ree and normal Marine limestone are basically identical.the coarse grain dolomite and saddle dolomite is related to hydrothermal process. the dolomitefrom second phase of the hydrothermal process or direct form under the cathodoluminescenceis generally dark rose red or not; the third phase of the hydrothermal process main formingseam hole authigenic saddle dolomite, who is shiny red roses. Geochemistry shows that thesecond phase of the hydrothermal process has two different diagenetic fluid source, and therelated dolomites is divided into two categories: the coarse grain II1type dolomite with loweroxygen isotopic values, higher composition of Mn and Mn/Sr value, rare earth elementdistribution patterns with Ce anomaly characteristics; comparing the coarse grain type II2dolomite and the saddle dolomite in the second phase of the hydrothermal genesis to coarsegrain dolomite II1type, the oxygen isotope is relatively higher, Mn content and Mn/Sr valueslower. The rare earth element distribution pattern has obviously abnormal characteristics ofEu anomaly. While the shallow buried powder–mesocrystalline to the euhedral dolomite anddirty hydrothermal transformation genesis of dolomite has a great role in the formation ofhigh quality reservoirs.According to dissolution time, dissolution development object, dissolution ways, and therelationship between the product of the dissolution with other related diagenesis, thedissolution stage are considered including syngenetic atmospheric water dissolution, and midcaledonian act the ith unconformity surface atmospheric water karstification, associated withorganic acid dissolution, the late hydrothermal dissolution dissolution. Contemporaneousstage atmospheric water dissolution is controlled by the development of sea level change andbeach grainstone distribution; Atmospheric water karstification are controlled by a room settop of unconformity surface; Dissolution associated with organic acid have regional andhorizon limitations, whose main development is in that dolomite with intergranular hole filledwith asphalt; The development of late hydrothermal dissolution is mainly controlled by thefirst pore, holes and fracture development. While the late hydrothermal dissolution processdeveloped late, the reservoir space resulted from corrosion is scarcely filled, which has greatcontribution to the high quality reservoir formation.The middle-lower ordovician carbonate reservoir all developed in platform and theplatform-marginal facies zone; the limestone reservoir’s and dolomite’ storage coefficient arequiet similar； the eagle mountain group is the focus of the horizon for the development ofvarious reservoir, the Yijianfang formation takes the second place,and Penglaiba formationlowest...