Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production

IF 4.2 3区 工程技术 Q2 ENERGY & FUELS
Guangyin Cai , Yifan Gu , Dongjun Song , Yuqiang Jiang , Yonghong Fu , Ying Liu , Fan Zhang , Jiaxun Lu , Zhen Qiu
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Abstract

Pore structure characteristics, gas content, and micro-scale gas occurrence mechanisms were investigated in the Shan23 sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images, low-temperature N2/CO2 adsorption and high-pressure mercury intrusion, methane isothermal adsorption experiments, and CH4-saturated nuclear magnetic resonance (NMR). Two distinct shale types were identified: organic pore-rich shale (Type OP) and microfracture-rich shale (Type M). The Type OP shale exhibited relatively well-developed organic matter pores, while the Type M shale was primarily characterized by a high degree of microfracture development. An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas, free gas, and total gas content under high temperature and pressure conditions. There were four main research findings. (1) Marine-continental transitional shale exhibited substantial total gas content in situ, ranging from 2.58 to 5.73 cm3/g, with an average of 4.35 cm3/g. The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption, followed by multilayer adsorption in clay pores. (2) The changes in adsorbed and free pore volumes can be divided into four stages. Pores of <5 nm exclusively contain adsorbed gas, while those of 5–20 nm have a high proportion of adsorbed gas alongside free gas. Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas, while pores of >100 nm and microfractures are almost predominantly free gas. (3) The proportion of adsorbed gas in Type OP shale exceeds that in Type M, reaching 66 %. (4) Methane adsorbed in Type OP shale demonstrates greater desorption capability, suggesting a potential for enhanced stable production, which finds support in existing production well data. However, it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development. These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.
鄂尔多斯盆地山23亚段海陆过渡页岩气赋存特征及其对页岩气生产的启示
利用扫描电镜、低温N2/CO2吸附和高压压汞、甲烷等温吸附实验和饱和ch4核磁共振等技术手段,对鄂尔多斯盆地东南缘山23亚段海陆过渡页岩孔隙结构特征、含气量及微尺度含气机制进行了研究。识别出两种不同的页岩类型:富有机质孔隙页岩(OP型)和富微裂缝页岩(M型)。OP型页岩有机质孔隙发育较好,M型页岩微裂缝发育程度较高。提出了一种结合破碎样品的甲烷等温吸附和塞样的ch4饱和核磁共振相结合的实验方法,以测定高温高压条件下的吸附气、游离气和总气含量。主要有四个研究结果。(1)海陆过渡页岩原位总含气量较大,为2.58 ~ 5.73 cm3/g,平均为4.35 cm3/g。吸附气主要通过微孔充注和多层吸附进入有机质孔隙,其次是粘土孔隙的多层吸附。(2)吸附孔体积和自由孔体积的变化可分为4个阶段。5 nm的孔隙只含有吸附气体,而5 - 20 nm的孔隙则含有大量吸附气体和游离气体。20 ~ 100 nm孔隙中自由气体比例较高,吸附气体较少,而100 nm孔隙和微裂缝中几乎以自由气体为主。(3) OP型页岩中吸附气的比例超过M型页岩,达到66%。(4) OP型页岩中吸附的甲烷具有更强的解吸能力,表明具有提高稳定产量的潜力,现有生产井数据也支持了这一观点。然而,必须强调的是,两种类型的高含气层段都为勘探开发提供了宝贵的机会。这些数据可以支持未来的模型验证,并增强勘探和开发海陆过渡页岩气的信心。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Natural Gas Industry B
Natural Gas Industry B Earth and Planetary Sciences-Geology
CiteScore
5.80
自引率
6.10%
发文量
46
审稿时长
79 days
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