Experimental study on the influence of coal-based CO2 geological storage on roof fracture conductivity
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摘要: 煤基CO2地质封存是温室气体减排的重要方式，但也存在地下CO2泄露的安全风险。为了评估煤基CO2地质封存的安全性，采集沁水盆地南部胡底矿3号煤顶板泥质粉砂岩样品，模拟实验研究“CO2-H2O-岩”反应中柱状试样人工裂缝形貌、全岩矿物组成与CO2导流能力变化。结果表明：方解石脉溶蚀、次生矿物充填与外部有效应力共同影响试样裂缝导流能力。原始渗透率为0.016×10–3μm2的低渗试样，方解石脉溶蚀导致实验前期渗透率升高；随着反应进行，有效应力主导下裂缝闭合，渗透率呈“先升后降”变化趋势；原始渗透率为3.785×10–3μm2的高渗试样，H2CO3不断溶蚀裂缝壁面长石等矿物，并产生高岭石等次生矿物混合充填于裂缝中，使渗透率持续降低。煤基CO2地质封存过程中，较高的注入压力导致顶板产生人工裂缝；CO2注入施工结束后，次生矿物充填及有效应力增大使裂缝导流能力快速下降，因此，煤中封存CO2沿顶板裂缝长期泄露的风险较低。Abstract: Coal-based CO2 geological storage is an important way to reduce greenhouse gas emissions, but there is also a safety risk of underground CO2 leakage. In order to evaluate the safety of coal-based CO2 geological storage, the roof samples of No.3 coal seam in Hudi Coal Mine, southern Qinshui Basin were collected, and the changes of artificial fracture morphology, whole rock mineral composition and CO2 conductivity of columnar samples in "CO2-H2O-Rock" reaction were studied by simulation experiments. The results show that calcite vein dissolution, secondary mineral filling and external effective stress jointly affect the fracture conductivity. For the low permeability samples with original permeability of 0.016×10–3μm2, calcite vein dissolution leads to the increase of permeability in the early stage of the experiment. As the reaction proceeds, the fracture is closed under the guidance of effective stress, and the permeability increases first and then decreases. For the high permeability samples with original permeability of 3.785×10–3μm2, H2CO3 continuously dissolves feldspar and other minerals on the fracture wall, producing kaolinite and other secondary minerals to fill the fracture, so that the permeability continuous to decrease. In the process of CO2 geological storage, high injection pressure leads to artificial roof fracture. After the completion of CO2 injection construction, the fracture conductivity decreases rapidly due to the filling of secondary minerals and the increase of effective stress, therefore, the risk of long-term leakage of CO2 in coal along the roof fracture is relatively low.
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Keywords:
- CO2 geological storage /
- roof /
- fracture /
- conductivity /
- permeability
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图 2 “CO2-H2O-岩”反应中试样气测渗透率变化
Fig. 2 Permeability changes of samples in the process of CO2-H2O-Rock reaction
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图 3 实验前后试样全岩矿物组成对比
Fig. 3 Comparison of whole rock mineral composition before and after the experiment
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图 4 LY-1试样表面矿物宏微观形貌变化
Fig. 4 Macroscopic and microscopic changes of minerals on the surface of LY-1 sample
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