Abstract: The Lower Triassic Baikouquan Formation is one of the main reservoirs in the Xinjiang Oilfield. Using the basic principle of
base-level cycles of high-resolution sequence stratigraphy, we systematically analyze the evolution of all base-level cycles and
high-resolution sequence stratigraphic model in the Baikouquan Formation of the Ma 18 block based on core data of 4 wells, and
logging and well-logging data of 122 wells. Results show that one long-term, three medium-term and eighteen short-term base-level
cycles were classified. Fan-delta front subfacies change to pro-fan delta subfacies from bottom to top during the Baikouquan period.
Based on the analysis of single sand body within the base-level cycles, it is indicated that at the bottom of the Baikouquan Formation,
the ratio between the growth rate of the accommodation space and the sediment supply flux is far less than 1.0 (A/S ≤ 1). As such,
channel sand body distributes contiguously mainly on progradation, and the configuration is in the form of cut-overlay type. In contrast,
in the middle of the formation, with the rise of base-level, the ratio of A/S increases and the sand body is distributed by contact. At the
upper part, the lacustrine level rises, while dynamic of river is weak. The sand body retrogrades back, and far bar appears. Sand body is
distributed separately. Favorable reservoir sand bodies are formed by underwater distributary channel during the mid-early phase of
long-term cycle. The lacustrine mudstones formed by late lacustrine transgression provides good cap rocks for hydrocarbon traps.

Key words: high resolution sequence stratigraphy, base-level cycles, single sand body, Baikouquan formation, Ma18 block, Mahu Sag