摘要
作者探讨了砂岩孔隙度非常低情况下气藏形成的若干问题。突出了晚期相对活动构造对孔渗条件起死回生的决定性意义。阐明低级别砂岩孔隙结构、毛管作用以及油气活动方式。研究了气在砂岩基质孔隙中活动的“似极限”和有效性、超致密砂岩演化史、普遍超高压、次生气藏等新问题。强调早期聚集和晚期改造的相辅作用。
The co-existence of both Upper Triassic organic-rich sediments and super-tight sand-stone is a very typical petroleum geological condition in Western Sichuan Basin.Theoil-generating peak period in the end of Middle Jurassic was just the time when originalporosity of the sandstone reduced and secondary porosity increased gradually.Favourable condition,combined with various traps formed earlier,formed the first upsurge of lateralmigration and accumulation.After continuous subsidence of more than 100 million yearsof the basin,the rocks were already getting super-tight (average Φ<7%),hydrocarbongenerating was slow down and turned to craking,and superpressure formed in sedimenta-ry rocks,thus resulting in the sluggishness of natural gas.Himalayan tectonic movementresulted in many new structural traps,and fractures connected pore spaces in the super-tight sandstone.This let to the second upsurge of both horizental and lateral migration andaccumulation.The porosity of supertight sandstone tended to be“pseudo-limit”of gas migration,thismade things more complicated for gas accumulation and recovery:1.Linear gas-poolgroups distributed along fracture system;2.Layer-like reservoirs formed by felty sand-stone with fracture system could be good anticlina gas pools with edge water drive,but thegas production would vary remarkably in different wells.However,this type of gas poolsare still the main targets for gas prospecting in West Sichuan.3.Porosity lower than the“pseudo-limit” (Φ≈2.5%,throat T≈10nm)is not valuable,but the gas would flow outfrom fracture belt suddenly into the wellbore and even make blowout sometime,then theproduction will decline rapidly.4.Gas fields with certain reserve might form in localplaces where better porosity of sandstone equivalent to the tight sandstone class (8%—15%) at the shallow formations or favourable facies and petrogenetics.The production ishigh when fissure developed in the sandstone;otherwise,it is low.This is another targetfor gas exploration.
出处
《石油与天然气地质》
EI
CAS
CSCD
北大核心
1993年第3期169-180,共12页
Oil & Gas Geology
