四川盆地东南地区林1井灯影组鞍形白云石成因及其意义

对四川盆地东南地区林1井上震旦统灯影组鞍形白云石的岩相学特征和碳、氧、锶同位素特征及流体包裹体成分与温度进行研究,认为它属热液成因。研究区热液活动在岩相学上表现为充填状鞍形白云石,发育鞍形白云石线状充填晶洞。鞍形白云石共生矿物包括石英、沥青等。鞍形白云石δ18O值和δ13C值异常偏负,87Sr/86Sr值异常偏高,与围岩差异明显。鞍形白云石原生流体包裹体均一温度为270～320℃,明显超过了该井最高埋藏温度;流体包裹体的气相部分以CO2、CH4和N2为主,液相部分以H2O和CO2为主。这些特征表明,形成鞍形白云石的流体来自于基底的热液,灯影组白云岩受热液溶蚀改造而发育热液改造型白云岩储层,并有过油气成藏过程。

Origin of Dengying Saddle Dolomite in Well Lin-1 in Southeastern Part of Sichuan Basin

Integrated analysis of petrography,isotopic geochemistry,fluid inclusions has shown that the Upper Sinian Dengying saddle dolomite from Well Lin-1 is relative with hydrothermal activity in origin.The saddle dolomite commonly coexists with quartz and bitumen.The saddle dolomite shows rather low values of δ18O(‰) and δ13C(‰) and very high values of 87Sr/86Sr,which is significantly different to those from the surrounding rock around Dengying Formation.Primary fluid inclusions in the saddle dolomite comprise of gaseous CO2,CH4 and N2 and liquidus H2O and CO2,Primary homogenization temperature of the inclusions is at 270-320℃,which is obviously higher than the maximum burial temperature of this area.It is suggested that the Dengying dolostone reservoir was altered by hydrothermal dissolution and hydrocarbon accumulation happened later in it.