| Carbonatite of Ordovician is key region for oil-gas exploration in inter-platformbasin that is widely developed in Tarim Basin with rich oil-gas resources. This papertakes reef flat facies of Ordovician around platform in Tarim Basin as object of studyand makes systematical analysis of sequence stratigraphy, sedimentary system,sequence-lithofacies paleogeographic and oil-gas reservoir geology for offering newmaterial to oil-gas exploration in Tarim Basin, all of which are guided by theory ofsedimentology, sequence stratigraphy, tectonic geology and seismic stratigraphySix sequence boundary types (surface of unconformity, karstification, watereroding and flooding, lithology and lithofacies transforming, overlap strata andmaximum marine flooding)are identified in Ordovician of Tarim Basin with guidanceof vail’s typical theory in sequence stratigraphy, so there are two second-ordersequence（sSS1and SS2）and fourteen third-order sequence（sSQ1-SQ14）. Synchronicstratigraphic sequence framework is built on discussion of development and sequenceevolution character of second-order sequences. Sedimentary facies and seismic faciesare carried out in sequence framework for making the best of field profile, drillingcores, logging, seismic and regional data. This paper identifies three sedimentarysystems such as carbonate platform, shallow-water shelf and basin, and manysub-face and micro-face types, of which characters are researched respectively. On thebasis above, sequence-lithofacies paleogeographic map of Ordovician in Tarim Basinhas been made with taking tract of second-order sequence as unit.This paper searches movement and distribution regulars of reef flat body withdetailed description of factors that control reef flat facies development anddistribution around platform in Tarim Basin, all of which are based on sedimentarysystem and sequence stratigraphy analysis. Study showed that paleogeographicposition, paleoclimate, geotectonic and change of sea-level control development ofreef in Ordovician of Tarim Basin. So early Ordovician platform edge has onenessand inheritance, late Ordovician platform edge has multi-subbranches andsegmentation. During depositional time of Yijiangfang and Lianglitage in Middle-lateOrdovician, the distribution of reef flat facies around platform shrinks to interior platform. And reef flat facies have moved twice in Upper Ordovician. With movementof No.10riftzone, the first phase which develop near No.1riftzone on North slope hasmigrated to No.10riftzone. The two phase superpose together for slope break in eastof South slope has moved a small distance, while west moved a little.It is the first time to make systematical search on the differences at sediment andreservoir in Yijianfang and Lianglitage formation of middle and north Tarim Basinand Bachu area during evolution of reef flat facies of Ordovician around platform inTarim Basin. And the differences mainly display in four aspects at sediment, such ashorizon where developed, distribution, lithologic association and sedimentarymicrofacies.1.On aspect of horizon where developed, the meaningful development time ofreef around platform mainly in Yijianfang and Lianglitage period.2.On aspect of distribution, reef mainly develop in carbonate platform ofsouthern Tahe oilfield, Lunnan area and Bachu region during Yijianfang period, whilein Lianglitage period,reef mainly develop in southern Tahe and middle Tarim Basinrespectively.3.On aspects of lithologic association and sedimentary microfacies, gentle slopetype carbonate platform exist in southern Tabei and Bachu area during Yijianfangperiod, which mainly develop platform margin reef that have bond and baffle patchreef. And during Lianglitage sedimentary period, remote steepened on Southern Tabei,where widely covered reef flat facies. North slope of Tazhong is edge-mosaic typecarbonate platform, and reef flat facies are consist of grain banks and skeleton reefwith high energy, the horizon where have reef flat body is stable,while south slope ofTazhong develop reef flat facies widely.On reservoir aspect, there are lithology, space and physical property. Reef flatfacies reservoirs of Yijiangfang formation in Bachu area has similarity in south ofTahe oilfield, while during Lianglitage sedimentary time, reef flat facies reservoirs inSouth of Tahe oilfield and Tazhong area are different in space types and quality ofreservoir. Analysis showed that different genetic mechanism such as property ofplatform, growth rate of carbonate and tectonic background in southern Tahe andTazhong region is the reason for different characteristic of reservoirs.On aspect of reservoir-cap rock assemblage, granula limestone section inLianglitage formation and overlapped Sangtamu formation consist of goodreservoir-cap rock assemblage; Reef flat body with mud in Sangtamu formation andmarlite in Qiaerbake formation consist of good reservoir-cap rock assemblage, because platform of Yijianfang formation in southern Tabei has great distance toburied-hill with weak affection by tectonic movement in late stage; Reef flat bodyaround platform and mud in Carbonic consist of good reservoir-cap rock assemblage,because Qiaerbake formation and Sangtamu formation in Bachu area are corroded byCaledonian tectonic movement... |
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