北塘凹陷新近系馆陶组的CO2-EATER实验研究

 地热尾水回灌率低是目前中国沉积盆地砂岩储层中-低温地热资源可持续开发利用的瓶颈。基于利用CO₂提高地热回灌率,即CO₂-EATER(CO₂-Enhanced Aquifer Thermal Energy Recovery)概念模式,以黄骅坳陷中部北塘凹陷新近系馆陶组砂岩热储层为例,利用高温高压反应釜实验模拟了反应时间为10d,温度为100℃,压力为10MPa人工注入CO₂条件下,水-岩-CO₂相互作用及其对储层水化学组分及矿物组分的改变和对孔隙度及渗透率可能的影响。结果表明,CO₂注入后,储层水的pH值从7.7下降到6.3,储层水的HCO₃^-、Ca、Mg、Na和K等组分显著增加。这是由于CO₂溶解于水,形成了酸性环境,储层中长石类矿物和方解石发生溶解而释放出金属阳离子。地层水的δ¹⁸O_H2O和δ²H_H2O分别发生了3.5‰和3‰的负漂移,表明人工CO₂的注入促进了水-岩反应。X衍射(XRD)和扫描电镜(SEM)分析结果也证实了长石类矿物的溶解,这对改善储层具有一定意义,也说明CO₂-EATER模式可能适合于北塘凹陷新近系馆陶组。

CO2-EATER Model on Guantao Formation of Beitang Sag

Low reinjectivity of geothermal waste water has become the bottle-neck for sustainable use of low-medium temperature geothermal resources widely found in sedimentary basins of China. Based on conceptual model of CO₂-EATER(CO₂-Enhanced Aquifer Thermal Energy Recovery). Tertiary sandstone reservoir of Guantao formation in Beitang sag of the Middle of Huanghua Depression is taken as a testing example. Water-rock-CO₂ reaction at a temperature of 100℃ and a pressure of 10MPa is carried out for 10d using high temperature & high pressure Parr, to understand the corresponding effects on component changes of formation water and minerals as well as formation porosity and permeability. Results show that after CO₂ injection, pH dropped from original 7.7 to 6.3 and components like HCO-3, Ca, Na and K showed significant rise. The reason is that dissolved CO₂ forming acidic conditions and cations like K, Ca and Na were released into formation water due to dissolution of feldspar and carbonate minerals, which are also confirmed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) results. Water isotopes results also indicate that artificial CO₂ addition into formation water accelerates water-rock interaction and leads to "Reversed oxygen-shifts" of δ¹⁸O_H2O and δ²H_H2O by 3.5‰ and 3‰, respectively. It can be concluded that CO₂ injection can stimulate the geothermal reservoirs and CO₂-EATER model is feasible for Tertiary Guantao formation of Beitang sag.