烃源岩和储层中沥青形成演化实验模拟及其意义

Experimental simulation and significance on bitumen formation in source rock and reservoir

碳酸盐岩是否为有效烃源岩一直存在不同观点。从有机岩石学方法入手,以沥青为研究对象,开展了低成熟泥灰岩烃源岩生烃、饱和原油白云岩原油裂解的模拟实验,并对各模拟温度点的样品,以及四川盆地寒武系页岩、震旦系—寒武系碳酸盐岩样品进行了沥青鉴定、定量及反射率测定。结果表明,不同模拟阶段的泥灰岩中沥青含量呈现出由低至高再降低的趋势,高成熟早期为沥青形成高峰期;泥灰岩烃源岩、寒武系页岩烃源岩中沥青赋存方式受有机质发育程度及非均质性影响,主要呈分散状分布,但在烃源岩的微孔缝发育处,沥青则呈相对富集状或脉状,震旦系—寒武系泥质碳酸盐岩中检测到与烃源岩中赋存状态一致的沥青(原生沥青),是其生烃的有效证据之一;白云岩原油裂解实验中沥青含量由高至低变化,沥青充填在孔隙和粒间缝中,呈粒状、块状或脉状分布,是储层次生运移沥青;烃源岩中镜质体反射率与沥青反射率之间具有较好的相关性,可用等效镜质体反射率来反映烃源岩成熟度;同一温度下,储层沥青反射率明显高于烃源岩沥青反射率,利用储层沥青反射率来反映烃源岩成熟度时会出现比实际偏高的现象。

There have been different views about the effectiveness of carbonate hydrocarbon source rocks.Studies on bitumen by organic petrological method,and experiments simulation on hydrocarbon-generating of low matured marl hydrocarbon source rock and oil cracking in dolomite from saturated oil have been carried out.Identification,quantification and reflectance for bitumen have been reviewed on samples from every simulated temperature point and Cambrian shale,Sinian-Cambrian carbonate rocks in the Sichuan Basin.It turned out that bitumen contents emerged the trend from low to high and then decreased.The early stage of highly matured period is the stage of peak period for bitumen formation.The largely scattered distribution of bitumen in hydrocarbon source rocks of marl and Cambrian shale is impacted by the development degrees of organic matter and heterogeneity.But in the place where microporous joints developed,the content of bitumen is relative enrichment or in vein.Native bitumen consistent with the state of bitumen of hydrocarbon source rocks can be found in Sinian and Cambrian system argillaceous carbonate rocks,which is one of the effective evidence of its hydrocarbon generation.Bitumen content on dolomite changes from high to low in crude oil cracking experiment,pore and intergranular seams are filled with bitumen,which are granular,block or vein distributional reservoir.A good correlation exists between bitumen reflectance and vitrinite reflectance of source rock in the secondary migration of bitumen.Maturity of source rocks can be measured by equivalent vitrinite reflectance.Bitumen reflectance in reservoir is apparently higher than that of bitumen at the same temperature.Maturity of source rocks would be higher than the actual value when it is expressed by reservoir bitumen reflectance.