For the water-soluble gas migration and release mode,the determining elements of gas reservoiring are the continuous migration of structural high,late uplift,and low relief structural and lithologic combination trap with good physical properties;
Gouxi structure is a stratigraphic-faulted nose, combination trap, which is bounded by reverse fault at the east side and by the wide Shenjiachang syncline at the west side, covers a large area and lately outcropped, indicating there existed good preservation conditions and a large gas source area, which made the trap becoming a favourable one for gas exploration.
the coalbed gas pools in shallow area are mainly of small to middle scaled structure trap gas pools,while in deep area they are mainly of larger scaled hydrodynamic and combination trap pools’ it is infered that the coal seam buried between 600 1500 m in the southwest of Liulin is the best region for further exploitation
Structural trap is the main exploration aim in the Xuanhan-Daxian area of the northeast of Sichuan Province,but the rate of success is very low. So,based on the reservoir prediction technique,the structural-lithologic complex trap exploration is gone into effect.
Exploration degree of the simple structural hydrocarbon reservoir is high, the rest resource is mainly reserved in the subtle trap of Silurian system, Devonian system, Carboniferous system, Triassic system, Jurassic system and Cretaceous system, so it is especially important to carry out the recognition and evaluation, of subtle trap such as the ultra-deeplayer & ultralow amplitude structure, the layer-lithologic trap, the structure-lithologic trap, and the composite trap in these systems.
The chief source rocks are Guadalupe(K 2 )marine shale and carbonate rocks,major reservoir rocks are the shore-riv er-delta quartzose sandstone of Upper Cretaceous to Oligocene,and regional cap rocks are Miocene Leon thick shale. The principal period for hydrocarbon migrat ion and accu-mulation occur after the Miocene. The traps are classified into t hree types:Tertiary trap group,Cretaceous trap group and composite trap group between Tertiary and Cretaceous in overthrust frontal belt.
Based on the classification of subtle traps in the world, they are divided into three types, namely lithologic-stratigraphic trap, hydrodynamic trap and composite trap. While lithologic-stratigraphic trap can be subdivided into three basic styles, including sedimentary trap, diagenetic trap and interface trap.
By use of this method,18 structural stratigraphic combination traps were found and 117 Carboniferous reservoir distribution areas were delimitated in many structures (or structural belts)as Datianchi structural belt,etc.
Based on the developmental features and spatial distribution characteristics of Carboniferous non-structural traps in the study area,it is believed that the overlap traps of Donghe Formation sandstone,lithologic traps of sandstones filling the eroded ravines and valleys in the central uplift and the combination traps in northern Arwati are relatively favorable exploration targets,of which the former two are the most favorable,thus priority should be given to them in exploration.
On the basis of a comprehensive analysis of combining the characteristics of the medium deep reservoir rocks with the reservoir formation history,it is proposed that the targets of prospecting the medium deep gas reservoirs should be the combination traps formed on the Yanshanian palaeostructural belt.