鄂尔多斯盆地东缘中—高煤阶煤储层微观孔隙—裂缝结构表征

Microscopic pore-fracture structure characterization of medium-high rank coal reservoirs from eastern margin of Ordos Basin

摘要

以鄂尔多斯盆地东缘本溪组8号煤层为研究对象，开展低压 CO₂ 吸附、低温 N₂ 吸附、高压压汞和微米 CT扫描等实验，对中—高煤阶煤储层的孔隙—裂缝结构进行全尺度表征，评价不同尺度的孔隙—裂缝结构特征，探讨变质程度对不同尺度孔隙—裂缝发育的影响。结果表明：研究区煤体积类型以微孔—裂缝双峰优势型为主，具有微孔与裂缝并存的双峰态特征，孔径主要集中在 0.3∼1.5 nm 之间和大于 1000  m 的范围内；微孔、介孔、宏孔和裂缝平均体积分别占总孔体积的 70.8%、16.0%、8.1% 和 5.1% 。微孔贡献 98.8% 的比表面积，是吸附气的主要赋存场所。中—高煤阶煤储层的孔隙—裂缝结构存在显著差异，随煤阶的升高，煤变质程度加深，微孔体积增加，裂缝体积呈先增加再降低后升高的变化规律，介孔和宏孔体积变化不明显；高煤阶煤储层中微孔体积占比更高，吸附性更强。该结果为鄂尔多斯盆地深层煤层气潜力评价及勘探开发提供支持。

Abstract

The development of deep coal reservoirs is the key approach to increasing reserves and production of coalbed methane. The Benxi Formation 8th coals in eastern margin of Ordos Basin were taken as the research object, based on the coal quality parameter test, experiments such as low pressure CO₂ adsorption, low temperature N₂ adsorption, high pressure mercury injection and micron CT scanning were carried out to characterize the pore-fracture structure of medium-high coal reservoirs with a full scale, the characteristics of pore-fracture structure at different scales were comprehensively evaluated, and the influence of metamorphism degree on the development of pore-fracture at different scales was also discussed. The results show that the coal volume type in the study area is mainly characterized by a dualpeak pattern of micropores and fractures, featuring the coexistence of micropores and fractures, and the pore size is mainly concentrated in the range of 0.3-1.5 nm and greater than 1000 m. The average volume of micropores, mesoporous pores, macropores and fractures accounted for 70.8%,16.0%,8.1% and 5.1% of the total pore volume, respectively. Micropores contribute 98.8% of specific surface area and are the main occurrence sites of adsorbed gas. There are significant differences in the pore-fracture structure of middle-high coal reservoirs. With the increase of coal rank, the metamorphism of coal rock was deepened, the volume of micropores increases steadily, and the volume of fractures increases first and then decreases and then increases, while the change of mesoporous and macro pores volume is not obvious. The coal reservoirs with higher coal rank has higher volume proportion of micropores and stronger adsorption. This result provides theoretical and data support for deep coalbed methane potential evaluation and exploration and development in Ordos Basin.

关键词

孔隙—裂缝 / 结构表征 / 煤储层 / 中—高煤阶 / 本溪组 / 鄂尔多斯盆地东缘

Key words

pore-fracture / structural characterization / coal reservoirs / middle-high coal rank / Benxi Formation / eastern margin of Ordos Basin

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基金资助

中国石化科技部项目(P24205)

重庆科技大学科研资助项目(ckrc20241208)