陆相页岩油勘探“进源找油”探索与思考——以渤海湾盆地歧口凹陷沙一段为例

Probing and Thinking on“Exploring Petroleum Inside Source Kitchen”of Continental Shale Oil Exploration—A Case Study of the First Member of Shahejie Formation in Qikou Sag,Bohai Bay Basin,China

基于源岩油气理论和“进源找油”思想,创建提出了陆相页岩油“六定”思路(定背景、定源岩、定储层、定区带、定资源、定甜点)勘探流程,剖析其地质特征及与常规勘探流程的显著差异,并以渤海湾盆地歧口凹陷沙一段为例进行了论述。按“六定”思路地质评价认为,歧口凹陷在古近纪湖盆扩张和咸化环境下,半深湖—深湖、滨浅湖—湖湾相区分布广泛,发育了多个斜坡构造带,页岩油形成和聚集背景有利。沙一下亚段暗色泥岩、油页岩、富有机质页岩发育,厚度大,分布广,主体处于成熟生油阶段,生烃条件好。受内、外物源共同控制,沙一下亚段形成大面积分布的多期重力流沉积粉—细砂岩和泥—微晶白云岩储层,平均厚度为12.7~70.0 m,叠置发育,连片分布,整体呈低孔、特低—超低渗。沙一下亚段源储一体,发育4类源储配置,源储叠合区主要分布在凹陷中心、宽缓斜坡的中—低斜坡区和中斜坡区,纵向上浊积席状砂岩油层与白云岩油层叠置分布,并与高斜坡及裂缝带砂岩常规油藏横向连片。两类页岩油地质资源量合计中值为5.86×108 t,剩余资源占比大于60%,埋深适中,勘探潜力较大。沙一下亚段已有多口探井钻获工业油流,页岩油富集受构造、微相、成岩共同控制,发育致密砂岩、白云岩2类甜点体和4个甜点段,歧北低斜坡、歧南斜坡、板桥斜坡、歧北中斜坡是歧口凹陷近期勘探的有利甜点区。基于“进源找油”思想提出:需高度重视碳酸盐岩烃源岩生烃贡献和分布研究;应开拓一些“非常规思维”,探源岩(区)挖潜力、究储层找甜点、常规非常规结合立体综合勘探;要持续探索和重点攻关页岩油甜点区(段)识别和评价方法技术,解决选区评价面临的技术难题。

Based on the unconventional thought of“source rock oil and gas”theory and“exploration into source kitchen”,the exploration process of continental shale oil“six determinations”thinking(determining the background,defining source rocks,fixing reservoirs,ascertaining plays,confirming resources and finalizing sweet spots)was innovatively established,its geological characteristics and significant differences with the conventional exploration process were analyzed,and the oil exploration process of the lower first member of Shahejie Formation(E 2-3 s 1)in Qikou sag of Bohai Bay Basin was disscussed as an example.Background analysis shows that semi-deep lake to deep lake and shore-shallow lake to lake bay facies areas are widely distributed,and multiple slope structural belts are developed in the environment of Paleogene lake basin expansion and salinization in Qikou sag,so that shale oil formation and accumulating background are favorable.Source rock evaluation indicates that dark mudstone,oil shale and organic-rich shale are developed in the lower first member of Shahejie Formation with large thickness and wide distribution,and the main body is in mature oil generation stage,so the hydrocarbon generation conditions are good.Reservoir evaluation believes that the development of reservoirs in the lower first member of Shahejie Formation is controlled by both internal and external sources,forming a large area of silty-fine sandstone with multi-stage gravity flow sedimentation and mud-microcrystalline dolomite reservoirs(the thickness is 12.7-70.0 m),overlapping development and contiguous distribution,showing low porosity and ultra-low permeability.According to the shale oil play evaluation,the lower first member of Shahejie Formation characterized by“source-reservoir one body”with four types of configurations between source and reservoir.The superimposed areas of sources and reservoirs are mainly distributed in the middle-low slope area and middle slope area of the gentle depression.Vertically,the turbidite sheet sandstone reservoir and dolomite reservoir are overlapped and horizontally connected with the conventional sandstone reservoirs in high slope and fracture zone.The resource evaluation reveals that the total median value of the two types of shale oil geological resources is 5.86×108 t,the remaining resources account for more than 60%,the buried depth is moderate,and the exploration potential is large.According to the prediction of sweet spots,several exploration wells have drilled industrial oil flow,and shale oil enrichment is controlled by structure,microfacies and diagenesis.There are two types of sweet spot layers consisted of tight sandstone and dolomite,and four sweet spot sections.Qibei low slope,Qinan slope,Banqiao slope and Qibei middle slope in Qikou sag are favorable sweet spot areas for recent exploration.Three suggestions for“exploration into source kitchen”are put forward after further consideration deeply.Firstly,the research on the hydrocarbon-generating contribution and distribution of carbonate source rocks should be paid more attention to in order to find out the center and strata of main source rocks.Secondly,from the perspective of the extension and development of“source-reservoir one body”feature and“source control”theory in unconventional field,some“unconventional thinking”should be opened up such as exploring the source rock(area)to tap all potential,studying all kinds of reservoirs to search for all kinds of sweet spots,carrying out comprehensive exploration combined with the research of conventional and unconventional hydrocarbon reservoir.Thirdly,it is necessary to continue to probe and focus on the methods and technologies of identification and evaluation for shale oil sweet spot layers and sections,so as to solve the technical problems in the evaluation of selected areas.