Organic geochemistry and reservoir characterization of the organic matter-rich calcilutite in the Shulu Sag, Bohai Bay Basin, North China
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- 作者：Xianzheng Zhao ; Qing Li ; Zaixing Jiang ; Ruifeng Zhang ; Haipeng Li
- 关键词：Pore type ; Tight oil ; Lacustrine carbonates ; Eocene ; Bohai Bay Basin
- 刊名：Marine and Petroleum Geology
- 出版年：March, 2014
- 年：2014
- 卷：51
- 期：Complete
- 页码：239-255
- 全文大小：8447 K
文摘
Although extensive studies have been conducted on unconventional mudstone (shales) reservoirs in recent years, little work has been performed on unconventional tight organic matter-rich, fine-grained carbonate reservoirs. The Shulu Sag is located in the southwestern corner of the Jizhong Depression in the Bohai Bay Basin and filled with 400-1000聽m of Eocene lacustrine organic matter-rich carbonates. The study of the organic matter-rich calcilutite in the Shulu Sag will provide a good opportunity to improve our knowledge of unconventional tight oil in North China. The dominant minerals of calcilutite rocks in the Shulu Sag are carbonates (including calcite and dolomite), with an average of 61.5聽wt.%. The carbonate particles are predominantly in the clay to silt size range. Three lithofacies were identified: laminated calcilutite, massive calcilutite, and calcisiltite-calcilutite. The calcilutite rocks (including all the three lithofacies) in the third unit of the Shahejie Formation in the Eocene (Es3) have total organic carbon (TOC) values ranging from 0.12 to 7.97聽wt.%, with an average of 1.66聽wt.%. Most of the analyzed samples have good, very good or excellent hydrocarbon potential. The organic matter in the Shulu samples is predominantly of Type I to Type II kerogen, with minor amounts of Type III kerogen. The temperature of maximum yield of pyrolysate (Tmax) values range from 424 to 452聽掳C (with an average of 444聽掳C) indicating most of samples are thermally mature with respect to oil generation. The calcilutite samples have the free hydrocarbons (S1) values from 0.03 to 2.32聽mg HC/g rock, with an average of 0.5聽mg HC/g rock, the hydrocarbons cracked from kerogen (S2) yield values in the range of 0.08-57.08聽mg HC/g rock, with an average of 9.06聽mg HC/g rock, and hydrogen index (HI) values in the range of 55-749聽mg HC/g TOC, with an average of 464聽mg HC/g TOC. The organic-rich calcilutite of the Shulu Sag has very good source rock generative potential and have obtained thermal maturity levels equivalent to the oil window. The pores in the Shulu calcilutite are of various types and sizes and were divided into three types: (1) pores within organic matter, (2) interparticle pores between detrital or authigenic particles, and (3) intraparticle pores within detrital grains or crystals. Fractures in the Shulu calcilutite are parallel to bedding, high angle, and vertical, having a significant effect on hydrocarbon migration and production. The organic matter and dolomite contents are the main factors that control calcilutite reservoir quality in the Shulu Sag.