普光气田及邻区碳酸盐储层沥青的分子地球化学研究

Molecular geochemistry of solid bitumen-bearing carbonate reservoir rocks from the Puguang Gas Field and nearby areas

从普光气田及邻近地区二叠系和下三叠统15个含沥青碳酸盐储集岩样品分步提取了自由态油气组分和油气包裹体组分,并且应用限定体系(金管)热解实验获取了固体沥青热解组分。各组分进一步做色谱和色谱-质谱分析获取了生物标志物组成。分析结果表明,从油气包裹体组分、自由态油气组分至固体沥青热解组分,伽马蜡烷/C31升藿烷比值依次增高。同时油气包裹体组分C23三环萜烷/(C23三环萜烷+C30藿烷)、C21/(C21+ΣC29)甾烷、C27重排甾烷/(C27重排甾烷+C27规则甾烷)、20S/(20R+20S)C29甾烷和αββ/(ααα+αββ)C29甾烷等成熟度指标与自由态组分相近,而明显高于固体沥青热解组分。根据分子指标,可以推断古油藏的原油来源于不同的烃源岩,早期充注的原油来源于下志留统烃源岩,具有较低的伽马蜡烷含量和较高的成熟度;晚期充注的原油来源于上二叠统烃源岩,具有较高的伽马蜡烷含量和较低的成熟度。固体沥青主要为晚期充注、来源于上二叠统烃源岩的原油裂解生气的产物。

Free and inclusion oils were recovered by sequential extraction from 15 solid bitumen-bearing carbonate reservoir rocks in the Puguang Gas Field and nearby areas, and then pyrolysates of the solid bitumens from these samples were obtained via confined pyrolysis experiments （gold capsules）. All three components of each sample were further analyzed by GC and GC-MS for the biomarker compositions. The analytical results demonstrate that the ratio of gammacerane/C31 homohopanes is highest in solid bitumen pyrolysates, followed by free oils and inclusion oils. In addition, the molecular maturity parameters, such as ratios of C23 tricyclic terpane/（C23 tricyclic terpane ＋ C30 hopane）, C21/（C21 ＋ ΣC29） steranes, C27 diasteranes/（C27 diasteranes ＋ C27 regular steranes）, 20S/（20R＋20S） C29 steranes and αββ/（ααα＋αββ） C29 steranes of the inclusion oils are similar to those of the free oils, but substantially higher than those of the pyrolysates of solid bitumens. Based on various molecular parameters, it is suggested that the oils of paleo oil reservoirs probably had different sources. The early charged oils were derived from the Lower Devonian source rocks and had lower gammacerane contents and higher maturity, while the late charaged oils were derived from the Upper Permian source rocks and showed higher gammacerane contents and lower maturity. The solid bitumens were mainly generated from the cracking of the late charged oils.