塔里木盆地巴楚地区奥陶系礁灰岩CO_2地质储存的溶解溶蚀特征

Characteristics of Dissolution of CO_2 Geological Storage Applied to the Ordovician Reef Limestone in Bachu Area of Tarim Basin

CO2地质储存是有效减少大气中CO2的重要途径,但礁灰岩会因超临界CO2环境而发生溶解,导致孔隙度扩大,影响其储层的CO2储量。以塔里木盆地巴楚地区奥陶系礁灰岩为例,在温度40℃～120℃、CO2分压8～20MPa条件下,对礁灰岩储层进行CO2地质储存的模拟试验,观察岩样在试验前后宏观、微观的表象变化,分析其溶解度和孔隙度的变化趋势。结果表明:礁灰岩的溶解度随温度的升高而减小,随CO2分压的增加而增大,且温度为主要影响因素;在相同的CO2分压以及温度较低和原孔隙度较大的条件下,超临界CO2对礁灰岩的溶蚀作用较强,孔隙度的增幅较大,但由于温度和CO2分压的双重作用,礁灰岩整体的孔隙度变化可忽略不计;在超临界CO2的注入过程中,随着地下水的流动,储层内的溶蚀程度有局部差异;入口处的单位体积储层内,若1 000倍单位体积孔隙水的超临界CO2流体通过时,礁灰岩的孔隙度可扩大约1倍。

CO2 geological storage is effective to reduce CO2 in atmosphere, but the reef limestone dissolves because of the supercritical CO2 environment, and affects the reserves of CO2. Ordovician reef limestone in Bachu area of Tarim Basin was taken as an example, COs geological storage applied to the reef limestone reservoir was simulated in the condition of temperature with 40 ℃-120 ℃ and partial pressure of CO2 with 8-20 MPa, the macroscopic and microscopic appearance changes of sample before and after the experiment were observed, and the variation trends of solubility and porosity were analyzed. The results show that the solubility of reef limestone decreases with the temperature increasing, and increases with the partial pressure of CO2 increasing, and the temperature is the main factor; the dissolution of supercritical CO2 on reef limestone is strong, and the increment of porosity is large in the condition of the same partialpressure of CO2, lower temperature and larger original porosity, but the change of porosity of reef limestone is negligible in whole because of the double action of temperature and partial pressure of CO2 ; the dissolution of reef limestone reservoir is partially different with the flow of groundwater in the process of supercritical CO2 injection; when supercritical CO2 fluid of unit volume pore water with one thousand times transits at the entrance of unit volume reservoir, the porosity of reef limestone can enlarge twice approximately.