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CO2-EATER Model on Guantao Formation of Beitang Sag |
LI Yiman1,2, PANG Zhonghe1, YANG Fengtian1,3 |
1. Key Laboratory of Engineering Geomechanics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China;3. College of Environmental and Resources, Jilin University, Changchun 130021, China |
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Abstract: 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 δ18OH2O and δ2HH2O 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.
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Received: 15 April 2013
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