Pre-Cretaceous Palaeogeomorphologic Feature and its Significance to Oil and Gas in Hinterland Area of Junggar Basin

Abstract

The structural setting of Jurassic and lower Cretaceous in the hinterland area of Junggar basin is simple, underdeveloped in anticlinal traps, the petroleum accumulation has distal and secondary characteristics, complicated hydrocarbon distribution pattern makes the exploration there very difficult. Structural reservoirs predominated in the oil and gas fields discovered in early stages, and only 2 high yield nonstructural oil reservoirs – X21 and X31 were discovered on the southeastern slope of Jidong nose arch. No breakthrough has been made in either Jurassic or lower Cretaceous in the hinterland area over the past 10 years. Based on dissection on X31 reservoir, this paper ascertains once more the pay zone age, determines the reservoir type as stratigraphic one, and believes that the trap origin is related to the residual pre-Cretaceous palaeo-salient. This paper suggests paying attention to Jurassic and lower Cretaceous stratigraphic hydrocarbon reservoirs in the exploration of the hinterland area, especially focusing on fine depiction of pre-Cretaceous palaeogeomorphology and analysis on its controlling role in stratigraphic hydrocarbon reservoirs. Based on the “fill a gap” principle, the Qingshuihe Formation Member I thickness image is adopted to reflect the pre-Cretaceous palaeogeomorphology of the study area, whose basic features are as follows: 1 near NW – SE palaeo-trough is retained by 2 uplifted areas, different width of slope areas occur between the palaeo-trough and the palaeohighs, and 1 apparent topographic slope break zone developed in south central part. Comprehensive analysis suggests that stratigraphic traps are developed in the palaeo-salient of slope area and the slope break zone where the petroleum accumulation conditions are favorable, which are the favorable places for stratigraphic hydrocarbon reservoir exploration.