Study On Paleostructure Characteristics And Its Evolution In Bachu-Maigaiti Area

Bachu arch-Markit slope is located in the central-western Tarim Basin and covers two II-grade tectonic units. The tectonic framework of Bachu area presented as“west-east differentiation and north-south dissimilitude”. The uplift developed faults with three orientations. On the longitudinal section, the deep fault systems are more developed than the shallow fault systems. The west fault systems are more developed than the east fault systems from the plane view. The NW faults piled up on the NW and NWW faults, and incised the NW faults. They formed later than NW ones. On the whole, the tectonic framework has the characteristic of“the early action was more intense than the late action and the degree of inversion is strong in the west but weak in the east”. Maigaiti slope is a regional monocline.The area underwent multistage tectonic movements forming a certain number of fault zone and unconformities. Faults in Bachu-Maigaiti area active in Hercynian and Himalayan period, significantly more pressure shear fracture. Some key faults, especially, Serikbuya fault, tumuxiuke fault and gudongshan faults were formed in middle of Caledonian movement, and became of important element which influence deposition and erosion in bachu-maigaiti region, and took a rather significant role in the later movement. The study showed that there exist eight unconformities in total development from Sinian to Quaternary. The important is the tops of Ordovician and Lower-Middle Devonian and the bottom of Mesozoic and Pliocence series, which could controll the types and distribution of reservoirs to a certain extent.Based on the work of previous people and the feature of abundant earthquake data, This article used back-stripping technology and formation architecture extension method to recovery the denudation quantity for every important unconformity, and reconstruct the paleostructure in lower-middle Ordovician in bachu-maigaiti area. we find out the tectonic framework is west higher while east lower in lower-middle Ordovician in bachu-maigaiti region, this is different from the now framework which is east higher west lower (bachu is a arch and maigaiti is a slope). The area was a north poured slope, southwest high and northeast low in Caledonian period. In the late Hercynian period, today’s Bachu arch begun to take shape, and Maigaiti slope occurred up side down. In Indosinian and Yenshan period, Bachu arch ulteriorly uplifted and abraded. In middle and late Himalayan period, Bachu arch ulteriorly uplifted and final fell into a pattern, at the same time, Maigaiti slope became today’s precipitous to the south.Most of native reservoirs, formed In Caledonian to late Hercynian period, were later modified with varying degrees of damage. The formation of the secondary reservoir in Indosinian and subsequent phases, were later modified of the lower damage. In Himalayas period, the Mesozoic and Cenozoic of bachu-maigaiti area were regional south-dipping, so that early reservoirs suffered reconstruction, oil and gas re-differentiation, adjust, and shallow oil and gas migration from south to north, forming new reservoirs.