Abstract: The Triassic Lower Oil Formation in Akeyasu of Tahe Oilfield is a nice thick reservoir-cap combination featuring in upper mud and lower sand, where shallow braided river delta and shore-shallow lacustrine sediments developed. The braided channel and mid channel of the delta plain intrafacies and the debouch bar of the front intrafacies constitute the main sand body of the Formation. Practical exploration indicated that thick massive channel sand body and debouch bar were main carriers of underground aquifer, oil and gas was mainly generated from the thin mid-channel sand body on the top and constituted local low-amplitude secondary oil and gas reservoirs characterized by upper oil and lower water. Investigating the cause showed that firstly oil and gas that migrated along the fault mainly accumulated in the channel sand body of Upper and Lower Oil Formations on the top, and the Lower Oil Formation had lower filling degree. Secondly, oil and gas was easily migrated and transported and difficult to be accumulated, due to the development of channel sand bodies of strong connectivity in Lower Oil Formation. Oil and gas could only be accumulated in mid-channel pinchout sand body that developed in low-amplitude structures, in addition, the distance of migration and transportation was so long that only low-amplitude structural-lithologic oil and gas reservoirs developed. Therefore, to determine the distribution range of mid-channel sand body and its superimposition relations to low-amplitude structures, and to make clear the time-space matching relation between channel sand and faults were critical to further exploration in Triassic Lower Oil Formation of Akeyasu

Key words: Tahe Oilfield, Akeyasu, Lower Oil Formation, sedimentary characteristics, oil and gas accumulation