准噶尔盆地吉木萨尔凹陷芦草沟组页岩油滞留聚集机理及资源潜力探讨

Residual accumulation and resource assessment of shale oil from the Permian Lucaogou Formation in Jimusar Sag

近些年来,北美地区海相页岩气的成功开发及致密油、页岩油的勘探突破,带动了全球在烃源岩层内寻找油气的热潮。准噶尔盆地吉木萨尔凹陷二叠系芦草沟组为一套半深湖—深湖相烃源岩,显示良好的页岩油勘探前景。基于岩心描述、薄片观察、地球化学（TOC、R_O、Rock-Eval等测定）、XRD、压汞、核磁共振等实验数据及资料,研究表明：①芦草沟组烃源岩厚度大,有机质丰度高,主要处于低熟—成熟阶段,为一套优质烃源岩;②页岩油储集空间类型为微裂缝和基质孔隙两大类,前者以纹层理（缝）为主,后者以粒间溶孔为主,大小一般为100～1 000nm。其中纳米级孔喉占孔喉总体约98%,是页岩油储集空间的主体。依据芦草沟组页岩油含量（S1）与TOC、R_O关系及页岩油（即滞留烃量）富集因素分析,综合研究认为芦草沟组中R_O值为0.7%～1.0%、TOC≥2.0%的烃源岩段是寻找页岩油的最有利层段,页岩油整体上具有＂有机质大量吸附,纳米级孔喉大量聚集,微裂缝（纹层缝）有效汇聚＂滞留聚集特征。基于页岩油评价的关键参数及核磁共振等实验结果,采用小面元体积法,初步估算凹陷内芦草沟组页岩油地质资源总量约为25.5×10^8t,（理论）可采资源量约为4.16×10^8t,技术可采资源量约为0.40×10^8t,其富集中心位于吉30井、吉174井、吉251井、吉32井等附近。这些认识对该地区页岩油勘探开发具有重要的指导意义。

In recent years,successful development of marine shale gas and rapid exploration of tight and shale oil in North America had driven petroleum exploration and development into the source rocks in the world.The Permian Lucaogou Formation in Jimusar Sag,Junggar Basin has been recognized as a series of semi-deep lake to deep lake source rocks,showing good prospect of shale oil exploration.Based on detaileddescription of cores,slice observation,organic geochemical analyses,mercury injection and nuclear magnetic resonance of the Lucaogou Formation,it is concluded as follows：（1）Source rocks of the Lucaogou Formation show large thickness,high TOC and low maturity to maturity;（2）The shale reservoir space mainly included microstructural fractures of lamination bedding and matrix pores.The latter mainly consists of dissolved intra-particle pores,which were generally 100-1 000 nm.The nano-size pore-throats are the main reservoir space with a ratio of 98% in the total space.Based on analyses of relationship among S_1 content,TOCand ROof source rocks from the Lucaogou Formation and enrichment condition discussion of shale oil,it is considered that sources rocks with ROranging from 0.7%to 1.0%and TOC≥2.0%are the favorable sections for shale oil and the residual hydrocarbon accumulation of shale oil has some characteristics,such as＂adsorption of organic materials,store in nano-size pore throats and flow in the micro-fractures＂.Key assessment parameters of shale oil and nuclear magnetic resonance analyses by the small patch method were used to preliminarily calculate the resources.Shale oil in Jimusar Sag have great potentiality with inplace resources of 2.55 billion tons,（theoretically）recoverable resources of 0.42 billion tons and technically recoverable resources of 0.04 billion tons,which are richly distributed around Well 30,Well 174,Well 251 and Well 32.These above understandings have important implication for shale oil exploration in Jimusar Sag.