A significant breakthrough has been made for the first time in the exploration of oil and gas reserves in the footwall of Manas structural belt at the southern margin of Junggar Basin. Well FT1 obtained high-yield oil and gas flow during oil testing in the Cretaceous Donggou Formation. The drilling and testing results of Well FT1

reveal as follows. (1)The condensate oil is derived from Cretaceous and Jurassic source rocks

while the natural gas is sourced from the highly mature Jurassic source rocks. The front belt of Manas thrust nappe is located within the effective hydrocarbon supply area of these two sets of source rocks. (2)The Cretaceous Donggou Formation develops large-scale

high-quality reservoirs. Braid river sand bodies in shallow water are stacked in multiple stages along the vertical profile

with a cumulative thickness of nearly 400 meters. Additionally

for the reservoir at a depth below 6 000 meters

the average porosity is 13.5 %

and the average permeability is 22 mD. Therefore

the footwall of Manas structural belt provides favorable reservoir conditions for high and stable hydrocarbon production. (3)The study establishes a complex overlapping structural model of deep thrust and shallow detachment at the northern foothills of Tianshan Mountains. The front belt

developed in the footwall of the large reverse fault on the structural flank

features large-scale in-situ structural traps with a shallower burial depth compared to the lower combination

offering significant potential for expanded exploration. (4)The front belt provides favorable accumulation conditions

characterized by "source rocks connected through thrust faults and lateral hydrocarbon sealing formed by overthrusts". Deep thrust faults connect with source rocks

facilitating the upward hydrocarbon migration

while overthrusts provide lateral sealing

thus forming a three-dimensional hydrocarbon accumulation pattern in the middle and lower combinations. The exploration breakthrough of Well FT1 has led to the discovery of a new exploration layers in the middle combination of the front belt of Horgos-Manas-Tugulu anticline group in the southern margin of Junggar Basin

confirming the natural gas resource potential of 100 billion cubic meters in the middle combination at the footwall of Manas structural belt. This breakthrough has changed the current exploratio

n status focusing on the lower combination while neglecting the middle and upper combinations

thus expanding the exploration horizons and domains for deep and ultra-deep oil and gas exploitation in the northern foothills of Tianshan Mountains. The favorable exploration targets for the middle combination in the front belt of southern margin of Junggar Basin are located in the footwall of overthrusts in major structures such as Manas

Tugulu

and Horgos. Five similar targets in the front belt have been preliminarily identified

covering an area of 320 km

2

with the estimated natural gas resources of 4 000×10

8

m

3

.