The Sequence Stratigraphy And Sedimentary Facies Of The Taiyuan Formation In The Daniudi Gas Field Of The Ordos Basin

The Carboniferous Taiyuan Formation is one of the major exploration targets of the Daniudi gas field in the Ordos Basin. As natural gas exploration becomes more and more difficult, it is very important to understand the sequence stratigraphic structure, sedimentary facies, and reservoir rocks distribution of the Taiyuan Formation clearly. The key target of sequence stratigraphy is to construct isochronous lithologic and lithofacies framework within which the sedimentary system are studied, and the reservoir rocks distribution can be predicted efficiently.Based on the fundamental principles of sequence stratigraphy and sedimentology, and by studying outcrop, core, seismic data, well log, the isochronal framework of the Taiyuan Formation is established, and the sedimentary facies are studied, and then the reservoir rocks distribution are predicted. After the sequence boundary within the Taiyuan Formation is identified, the sequences and system tracts are analysed. Through sequence stratigraphic subdivision and correlation of key wells, the Taiyuan Formation is divided into two 3rd sequences, and each of the member Ct1 and member Ct2 is a 3rd sequence. Sequence I mainly develop TST and HST, and Sequence II develop LST, TST and HST. The sequence stratigraphic framework and model are also established. The LST of Sequence II develop the incised valley, and the discovery of the incised valley may be helpful to the further gas exploration.Based on core, well log, seismic data, outcrop, and thin sections, the sedimentary facies within the sequence stratigraphic framework of the Taiyuan Formation are studied. The TST of Sequence I develop barrier shoreline system which contain barrier island, tidal delta, tidal channel, tidal flat, and lagoon. The HST of Sequence I mainly develop swamped lagoon. The LST of Sequence II mainly develop braided stream, and the main sedimentary facies are channel bar. The TST of Sequence II mainly develop transgressive limestone and mudstone, and the HST of Sequence II mainly develop strand plain and offshore deposits. The reservoir rocks are mostly contained within the TST of Sequence I and the LST of Sequence II.Through the sedimentary study within the isochronous sequence stratigraphic framework of the Taiyuan Formation, the sedimentary facies and the assemblage characteristics of sandstone, mudstone, coalbed, and limestone are analysed. The natural gas accommodation model is also summarized. We slao find that the size and composition of the sandstone particles have a strong effect on the porosity and permeability. At last, the favorable districts for further gas exploration are pointed out.