不同阶煤超临界CO2驱替开采CH4试验研究

Experimental research on supercritical CO2 enhanced coalbed methane recovery in different rank coals

由于地质成因与孔裂隙结构的差异,不同阶煤的渗透性与驱替开采CH 4效果不同。为研究超临界CO 2在不同变质程度煤体中驱替开采CH 4的效果,利用尺寸为100 mm×100 mm×200 mm的原煤试件,在恒定的温压(50℃,25 MPa)条件下,以10 MPa超临界CO 2驱替压力对4种不同变质程度的煤(弱黏煤、气煤、1/3焦煤和无烟煤)展开试验研究,结果表明:①不同煤阶煤体的孔隙形态与发育程度有较大差异,弱黏煤孔隙类型以墨水瓶型为主,无烟煤孔隙为狭缝型,而气煤与1/3焦煤则为楔形或平行板孔;对比孔隙比表面积,无烟煤与弱黏煤相对较高,分别为259.6510,154.0669 m 2/g,而气煤与1/3焦煤较低,分别为71.2359,41.4201 m 2/g;②煤渗透率受成矿地质环境和构造活动等导致的煤体结构、变质程度、裂隙发育程度、煤岩组成等多种因素的影响,在相同的有效应力下,4种测试煤样渗透率随变质程度升高而逐渐降低,驱替过程中CO 2注入量也随变质程度升高而降低,在25 MPa围压、10 MPa注入压力条件下,弱黏煤、气煤、1/3焦煤和无烟煤的渗透率分别为4.58×10-18,2.75×10-18,0.91×10-18和0.05×10-18 m 2,驱替实验结束时,CO 2注入量分别为18.13,6.45,5.01和0.78 mol;③4种煤试件的CH 4产出率和CO 2储存量均表现为气煤>1/3焦煤>弱黏煤>无烟煤,孔隙以楔形或平行板孔为主、比表面积较低、渗透率中等的气煤与1/3焦煤驱替置换效果相对较好,反映了超临界CO 2驱替开采CH 4效果是不同变质程度煤孔隙形态、发育程度以及渗透率的综合表现。

Due to the difference in geological genesis and pore fissure structure,the permeability and the effect of enhanced coal bed methane recovery in different rank coals are variable.To study the effect of supercritical CO 2 enhanced CH 4 recovery in different rank coals,some experiments were conducted in weakly caking coal,gas coal,1/3 coking coal and anthracite,respectively.Four coal specimens in the dimensions of 100 mm×100 mm×200 mm were investigated at the temperature of 50℃and the confining stress of 25 MPa.Supercritical CO 2 injection pressure was maintained at 10.0 MPa.The experimental results showed:①The pores configuration and porosity are different for the four different rank coals.The main pore type in the weakly caking coal is ink-bottle pore,anthracite is narrow-slit pore,while the pore types of gas coal and 1/3 coking coal are wedge pore or parallel plate pore.Anthracite and weakly caking coal have relatively high pore surface areas of 259.6510 m 2/g and 154.0669 m 2/g respectively,while gas coal and 1/3 coking coal have relatively low pore surface areas of 71.2359 m 2/g and 41.4201 m 2/g respectively.②Coal permeability was affected by many factors such as coal structure,coal rank,fracture,coal composition,etc.,due to ore-forming geological environment and tectonic activity.Permeabilities of four tested coal samples decreased with the coal rank,and the permeabilities in weakly caking coal,gas coal,1/3 coking coal and anthracite were 4.58×10-18,2.75×10-18,0.91×10-18 and 0.05×10-18 m 2,respectively at 10 MPa injection pressure.CO 2 injection amounts decreased with coal rank,which were 18.13,6.45,5.01 and 0.78 mol in the weakly caking coal,gas coal,1/3 coking coal and anthracite,respectively.③The results of CH 4 recovery rate and CO 2 sequestrated volume show that gas coal is better than 1/3 coking coal,weakly caking coal and anthracite.The effect of supercritical CO 2 enhanced CH 4 recovery of gas coal and 1/3 coking coal with wedge pore or parallel plate pore,low surface area and medium permeability is relatively good,which is a comprehensive expression of pore configuration,porosity and permeability in different rank coals.