准噶尔盆地玛湖凹陷二叠系—三叠系构造层序格架与沉积叠合演化.

Mahu sag is an important hydrocarbon-rich sag and a large stratigraphic lithologic reservoir exploration field in the northwestern Junggar Basin, forming a large stratigraphic lithologic reservoir with multiple layers. In order to find out the distribution law of oil and gas in this area and provide geological basis for the next exploration deployment, based on core observation and comprehensive analysis of seismic, logging and other data, the structural sequence analysis method was applied to study the main oil and gas reservoir series from Permian to Triassic. The results show that there are many large stratigraphic unconformity surfaces from Permian to Triassic in Mahu sag, which can be divided into Lower Permian, Middle Permian, Upper Permian-Triassic and other structural sequences. From Permian to Triassic, it experiences three major evolution stages of fault depression, depression and large depression slope, forming the superposition of three major structural sequences. The Lower Permian is a dustpan structural sequence formed under the extensional tectonic background; the northern stratum is thick, and the southern stratum is thin; it is deposited under the dustpan structure background of deep north and shallow south; the depression area is widely distributed fine-grained mixed rock, which is constructed of high-quality hydrocarbon source rock, and gradually becomes sandstone and conglomerate towards the slope area. The Middle Permian is a structural sequence with thick central and thin peripheral margins under the tectonic background of depression; the basin margin fan delta is developed, which is characterized by large basin, shallow water, limited basin margin fan body, and interbedded sediment of sand and mud in the basin. In Upper Permian-Triassic, Mahu area is located in the northwest slope area of Junggar large depression basin; under the background of shallow water, gentle slope and lacustrine transgression, the large retrogressive fan delta deposits are formed, and the sand bodies are vertically superimposed and horizontally distributed. The vertical superposition of the three major structural sequences forms the multi-layer distribution of stratum-lithologic or structure-lithological reservoirs in the area. [ABSTRACT FROM AUTHOR]