Characteristics of tidal action sedimentary system and distribution of favorable sand bodies of Silurian in Tazhong area, Tarim basin, NW China

The 3rd upper sub-member of the Silurian Kepingtage formation has developed marine clastic sediments and is an important petroleum exploration and development set in Tazhong area, Tarim basin, NW China, of which the sedimentary system and favorable reservoir distribution have been researched in detail based on the drilling, logging, seismic, experimental data and the theory of sequence stratigraphy. The results show that it was overlap and edge away layer by layer from northwest to southeast. On the background of marine transgression, the depositional systems of tidal flat, estuary and tidal reformation delta were developed and controlled by palaeogeomorphology, while different types of sand bodies and sedimentary formations were developed owing to the difference of types and energies of main action water bodies. In the sedimentary system of tidal flat, the main types of sand bodies are subtidal tidal channels which show significantly banded distribution vertical to the coast with a complete three-tier structure. The sand bodies of tidal bars are common in the estuary sedimentary system and extend far parallel to the axis of the estuary with thin layers of mudstone. The sand bodies of underwater distributary channels are developed with upward-finning positive rhythm and large erosion surfaces in the tidal delta sedimentary system and distributed like a bird-foot shape. By above research, the depositional mode of tidal flat-estuary-delta in Tazhong area has been established and the distribution of favorable reservoirs has been predicted.