Abstract:

Dachiganjing structural belt in the east margin of the Sichuan Basin which is com-posed of reversed linear high anticlines and hidden linear low anticlines under the reversed wing is a successful example in trapping gas in the main structure and the hidden structure under the circumstances that the high anticlines have been denuded partially and subjected to karst immersion on the shallower part.The main gas-bearing beds are Carboniferous soluble-pore dolomites and karst fissure limestones of the Permian Yangxin Series,the lat-er will be the main exploration target in after years The gas pools are mainly controlled by structural trap and gas-water differentiation distributed above-2500m in the main strucutre and above-4100m in the hidden structure.Scatters seriously the gas in the gas-bearing dolomites and limestones of the first member of Triassic Jialingjiang Formationdue to water immerion.The distribution of gas pools is dominated by“Water-immerion window”,structural trap and gas-water gravity differentiation,so gas is primarily preserved in the south plunging end of the main structure.The main difficulty for pre-exploration is hard to identify the structures formed by steep dipping beds through the seis-mic prospecting,thus the localities of exploration wells are almost always inaccurate.Ifwe could set the well localities on high positions to the best of one's ability,the efficiencyof success would be able to raise.Since the hidden low anticline which is closely related to the reverse of steep wing was formed late,the gas has less scatter and abundant reserve,it will be one of the main areas for gas exploration.Water of hydration differs from gra-vity water in physical properties,so their preservati on conditions and moving regular itiesare different.It is undoubtedly in appropriate to lump together the two when analyse the pressure field and gas-water relationship.As gas-producing fracture is a kind of linear medium,the“balance drilling”theory is not suitable for fracture gas pools.If we could prepare a kind of well-controlled device of high property and sufficient safety and developgas-obtaining technique from gush,we would be able to make a new breakthrough in the exploration of fracture-type gas pools.