Sedimentary Sequence And Favorable Reservoir Prediction In Tazhong Uplift, Tarim Basin

The Lower Paleozoic marine carbonate rocks of Tarim Basin has great propects for oil and gas exploration, and the Lianglitage Formation of Tazhong area is the most important reservoir. Sediment features, sequences and facies associated with them and the principal control factors of effective reservoir are urgent problems to be sovled.Based on 3D seismic data, well logging data and plenty of well core and thin-sections, with the use of methods of carbonate sequence stratigraphy, carbonate sedimentology, seismic sedimentology, this study focuses on the sedimentary feature of Lianglitage Formation, and facies models within sequence framework, especially the distribution patterns of organic reef and carbonate sand bank(reef-bank). Also the main factors of reef-bank reservoir are researched, at last the favorable reservoir are predicted.Lianglitage Formation is recongnized as one 2nd order sequence using the comprehensive analysis of seismic and well logging data, with the karst unconformity at the bottom and the drawing unconformity on the top. It can be further devided into three 3rd sequences. Sequence O3l-1 and O3l-2 are complete sequences comprised of highstand and transgressive system tract, on the contrast, sequence O3l-3 only contains the latter. Based on well logging data and well core, 4~6 4th sequences in each 3rd sequence can be recognised.Use the casting thin section, the lithofacies are detailed studied, which can be devided into 15 types, and 3 lithofacies associations. The general characteristic is shallowing-upward cycle. Combining the analysis of seismic sedimentology, carbonate platform can be devided into 2 facies areas, 4 facies and 11 subfacies. Lianglitage Formation along the Tazhong No.1 fault zone shows multicycle feature with reef-bank.Reef-bank is the most favorable facies for oil reservoir and usually well developed in highstand system tract, and controled by Tazhong No.1 fault zone according to sequence and facies profiles established by wells. The reservoir space types of reef-bank are various and well studied. 3rd sequence boundaries and high frequency cycles interfaces play vital role in reservoir improvement, and karstification related to tectonic uplift also helps increase porosity and permeability.Main lithological and stratigraphical traps were generalized, and on this basis seval favorable exploration zones are indicated such as platform margin reef-bank and platform interior bank with penecontemporaneous karst complex, and high uplift karst zone.