四川盆地震旦系灯影组深层碳酸盐岩储层沥青赋存形态及其油气藏示踪作用

Occurrence morphology of bitumen in Dengying Formation deep and ultra-deep carbonate reservoirs of the Sichuan Basin and its indicating significance to oil and gas reservoirs

四川盆地上震旦统灯影组钻井及其周缘露头剖面均可以见到丰富的沥青。作为古油藏裂解形成的产物,碳酸盐岩储层中沥青的赋存形态和分布特征等有助于揭示(古)油气藏保存、运移等关键信息。为了给四川盆地和我国西部盆地的深层—超深层油气勘探提供参考依据,基于灯影组四段岩心薄片观察、扫描电镜—能谱元素分析、流体包裹体有机地球化学分析等方法,系统研究了四川盆地高石1井等深层—超深层碳酸盐岩储层沥青赋存形态特征,揭示了其与油气成藏关键性事件的耦合性。研究结果表明,灯影组四段深层—超深层储层固体沥青具有两类赋存形态特征,第一类为储层沥青呈环边状附着于孔隙洞壁上或呈黏连枝状赋存于孔隙中间(如川深1井、高石1井),该类沥青有较明显的原地热解形成的收缩缝和残余孔隙,结合流体包裹体与埋藏热史等,能够有效示踪古油藏热裂解为碳质沥青后,古气藏保存至今;第二类为储层沥青呈颗粒状、条带状散乱的分布于孔隙内新生矿物晶体晶内、晶间(如马深1井、五探1井),并且沥青碎裂边界明显,它们揭示古油藏热裂解为碳质沥青后,古气藏泄压、气逸散,新生流体矿物进入储层堵塞孔隙的过程。结论认为,深层—超深层碳酸盐岩储层沥青赋存形态和分布特征能够有效示踪古油藏和气藏的成藏调整过程。

Abundant bitumen can be discovered in the wells of Upper Sinian Dengying Formation in the Sichuan Basin and their peripheral outcrop sections.As the cracking product of a paleo-oil reservoir,the occurrence morphologies and distribution characteristics of bitumen in carbonate reservoirs can indicate the preservation,migration and other key information of(paleo-)oil and gas reservoirs.In order to provide reference and basis for the deep and ultra-deep oil and gas exploration in the Sichuan Basin and the basins in western China,this paper systematically studies the occurrence morphological characteristics of bitumen in deep and ultra-deep carbonate reservoirs in the wells Gaoshi 1 of the Sichuan Basin by carrying out thin section observation,scanning electron microscope–energy spectrum analysis and fluid inclusion organic geochemical analysis on the cores of the fourth Member of Dengying Formation(Deng 4 Member).In addition,the coupling relationship between the occurrence morphology of bitumen and the key event of hydrocarbon accumulation is revealed.And the following research results are obtained.First,the solid bitumen in the Deng 4 Member deep and ultra-deep reservoir has two types of occurrence morphology.The first type of bitumen adheres to pore walls in the shape of a rim or exits in pores in the form of sticky branch(e.g.Wells Chuanshen 1 and Gaoshi 1).There are more obvious contraction joints and residual pores generated by in-situ thermal cracking in this type of bitumen.And combined with fluid inclusion and burial thermal history,it can effectively indicate that a paleo-gas reservoir has been preserved so far since the paleo-oil reservoir was thermally cracked into carbonaceous bitumen.The second type of bitumen is distributed at intra-and inter-neogenic mineral crystals in pores disorderly in the shape of grain and band(e.g.Wells Mashen 1 and Wutan 1)and it has obvious breaking edges.It reveals that after a paleo-oil reservoir was thermally cracked into carbonaceous bitumen,the paleo-gas reservoir suffered blowdown and gas escape and neogenic fluid minerals moved into reservoirs to fill in pores.In conclusion,the occurrence morphologies and distribution characteristics of bitumen in deep and ultra-deep carbonate reservoirs can effective indicate the hydrocarbon accumulation and evolution process of paleo-oil and gas reservoirs.