Sequence Stratigraphy Of Upper Devonian-Carboniferous In Tarim Basin

The basic geologic research in Tarim basin which is full of abundant hydrocarbon resource and multi oil generative assemblage and reservoir strata now can't meet the need of exploration and development. Taking Tarim basin upper Devonian - carboniferous as research target and based on classic theory of sequence stratigraphy and predecessor research result, this paper takes advantage of outcrop data, seismic data, drilling data and core data in and around Tarim basin and advanced technical measure and means and establishes sequence strata depositional model of craton basin in the base of sequence stratigraphy comprehensive research and figures out distribution laws and evolution feature of sedimentary system and facies in sequence framework, then analysis and evaluates source -reservoir-cap rock assemblage and propose favorable exploration area.Based on comprehensive sequence stratigraphy research integrated seismic data, outcrop data, drilling-logging data with core data, for the first time ,six standard third order sequences can be identified in upper Devonian and Carboniferous in total Tarim basin. The Donghe sandstone presents one integrated third order sequence (D₃sq), and the sequence boundary isâ… type. Five third order sequences can be identified in Carboniferous, which are Csq1, Csq2, Csq3, Csq4-, Csq5. Csq1 and Csq4 are integrated third order sequences that the sequence boundaries areâ… type. Csq2 and Csq3 areâ…¡sequence including Transgressive systems tract and Highstand systems tract. Csq5 isâ…¡type sequence, which presents Transgressive systems tract only, Highstand systems tract having been erode mostly. The division scheme is correspond with Vail classical sequence stratigraphy models.During deposition of Donghe sandstone, the Paleogeographic physiognomy presents a generalized incised channel which indicates NEE-SWW direction. Integrated with around stratigraphy and sedimentary analysis, this channel is a great strait opening in two ends and connecting with ocean , which is clipped by north and south uplift. The sedimentary environment and lithology facies of Donghe sandstone change very complexly, and the facies can't be explained by simply shore facies. The facies of Donghe sandstone include wave shore, tidal shore, estuary (or delta controlled by tidal), fan delta and shelf at least.After study of sedimentary facies of Carboniferous, it can be concluded that clastic facies consisting of tidal facies, lagoon facies, Fluvial facies, alluvial fan facies and fan delta and carbonate facies including evaporation platform, restrict platform, open platform and ford of platform margin. Totally, Transgressive systems tract mainly develop carbonatite deposition, such as bioclastic limestone interval, standard carbonate interval and Xiaohaizi carbonate interval. But Highstand systems tract mainly presents clastic tidal and fan delta. This sedimentary facies distribution model reflects that coming and going of sea water controls the ratio of clastic rock and carbonate rock.The physical property of Donghe sandstone interval changes greatly on plane. The physical property of Donghe sandstone interval in Tazhong area is better than in Tabei area. The reason for those is that the Donghe sandstone interval in Tabei area is cemented by carbonate seriously. Physical property of the same area change greatly vertically too. Reservoir physical property presented in Highstand systems tract is better than in Transgressive systems tract, and controlling of sedimentary system to reservoir presents obviously.The reservoir types of Carboniferous include clastics rock and carbonate rock. Clastic rock reservoir mainly distributes in Pebbled sandstone interval in Bachu formation and Sand shale interval in Kalashayi formation. Physical property of Sand shale interval is better than Pebbled sandstone interval obviously. That is physical property of fan delta is better than fluvial and alluvial fan. The physical property of dolomite and calcareous dolomite deposited in evaporate platform facies and calcsparite grainstone deposited in open platform facies and platform edge ford facies in carbonatite reservoir is better.There are three main associations of reservoir and cap rock in the sequences framework. The first one association is Sand shale interval in Carboniferous and Xiaohaizi calcareous rock which is better one. The second association is bioclastic limestone interval and middle-up mudstone interval which is poor one. The third association is Pebbled sandstone interval, Donghe sandstone interval and down mudstone interval which is better one. Good source rock present in Transgressive systems tract of Csq2 and Csq4, and there are two distributions zones for good source rock. The first one is well Hetian 1-well Ma 4 zone, the second one is the west area of south west Tarim basin.Whether clastic reservoir in Donghe sandstone interval and Carboniferous or carbonate reservoir in Carboniferous, the well area of Tazhongl8-Tazhong40-Tazhong4 are very favorable exploration area. The physical properties of this area are good, and trap types are various. Dolomite deposited in evaporation platform in Bachu area is also favorable reservoir. On the whole, oil source and migration pathway are key factors for development of giant oilfield.