断陷湖盆湖相页岩油形成有利条件及富集特征——以渤海湾盆地沧东凹陷孔店组二段为例

有别于北美海相页岩油气,中国湖相页岩油地质特征十分复杂,湖相页岩油是否具备形成的条件、如何寻找富集层段等问题亟待解决。为了探究湖相页岩油形成的有利条件与富集特征,以渤海湾盆地黄骅坳陷沧东凹陷孔店组二段为例,综合利用G108-8井、GD12井和GD14井3口取心井的635.8 m取心资料、12 000余块次分析化验资料及20口井的试油、试采资料,从页岩油形成的烃源岩、沉积组构及热演化等方面,对湖相页岩油成藏机理等进行了系统分析。研究结果发现：广泛分布多类型高丰度有机质、高脆性矿物组成、高密度纹层结构及中等热演化阶段是页岩油形成富集的主要条件;湖相页岩层系可划分为纹层状长英质页岩、纹层状混积质页岩、薄层状含灰白云质页岩及厚层状含灰白云质页岩4类组构相,处于中等热演化成熟阶段的纹层状长英质页岩、纹层状混积质页岩组构相为最优组构相类型;S₁^*/TOC值（以单位有机碳的含油量表示）平均大于135 mg/g、滞留烃含量大于阈值100 mg/g的超越效应明显,揭示了"优势组构相-滞留烃超越效应"的页岩油富集特征。采用这一新认识有效指导了页岩油勘探,研究区GD1702H井最高产油量达61 m³/d,自喷生产已超416 d,产量基本稳定在17 m³/d,GD1701H井、GD1702H井两口水平井累积产油量超1.4×10⁴t,证实了中国东部湖相页岩油具备工业性开发的良好潜力。

Favorable formation conditions and enrichment characteristics of lacustrine facies shale oil in faulted lake basin: a case study of Member 2 of Kongdian Formation in Cangdong sag,Bohai Bay Basin

Different from the North American marine facies shale oil, the China lacustrine facies shale oil presents very complex geological characteristics. It is urgently required to find out whether the geological conditions are suitable for the formation of lacustrine facies shale oil, and how to locate the enrichment zones of shale oil. This paper takes the Member 2 of Kongdian Formation of Cangdong sag in the Huanghua depression of Bohai Bay Basin as an example to explore the main controlling factors and enrichment characteristics of lacustrine facies shale oil. Comprehensively using the 635.8 m cores from Well G108-8, GD12 and GD14, analytical test data of more than 12 000 pieces of core samples, as well as well testing and pilot production data of 20 wells, the accumulation mechanism of lacustrine facies shale oil have been analyzed in terms of source rock, sedimentary texture and thermal evolution. The study shows that widely distributed, multi-type and high abundance organic matter, composition of highly brittle minerals, high-density laminaed structure and moderate thermal evolution are the main factors for shale oil formation and enrichment. The lacustrine shale strata are classified into four types of tectonic facies, i.e., laminated felsic shale, lamellar diamictic shale, thinly laminated limy dolomite shale and thick laminated limy dolomite shale. It has been confirmed that laminated felsic shale and lamellar diamictic shale in the moderate thermal evolution stage have the best tectonic facies, and the S₁^*/TOC is greater than 135 mg/g. This has revealed the shale oil enrichment characteristic of "favorable tectonic facies and transcendence effect of retained hydrocarbon". The new understanding can effectively guide shale oil exploration. Thus, Well GD1702H achieved the highest daily oil production of 61 m³; the natural flow well has been producing over 416 days, and the production is basically stabilized at 17 m³/d. Two horizontal wells, GD1701H and GD1702H, have a cumulative output exceeding 14 000 tons, proving that the lacustrine facies shale oil in the eastern China has a good potential for industrial development.