QICS Paper: Detection and monitoring of leaked CO2 through sediment, water column and atmosphere in a sub-seabed CCS experiment

Carbon capture and storage in sub-seabed geological formations (sub-seabed CCS) is currently being studied as a realistic option to mitigate the accumulation of anthropogenic CO2 in the atmosphere. In implementing sub-seabed CCS, detecting and monitoring the impact of the sequestered CO2 on the ocean environment is highly important. The first controlled CO2 release experiment, Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage (QICS), took place in Ardmucknish Bay, Oban, in May–September 2012. We applied the in situ pH/pCO2 sensor to the QICS experiment for detection and monitoring of leaked CO2, and carried out several observations. The cabled real-time sensor was deployed close to the CO2 leakage (bubbling) area, and the fluctuations of in situ pH and pCO2 above the seafloor were monitored in a land-based container. The long-term sensor was placed on seafloor in three different observation zones. The sediment pH sensor was inserted into the sediment at a depth of 50 cm beneath the seafloor near the CO2 leakage area. Wide-area mapping surveys of pH and pCO2 in water column around the CO2 leakage area were carried out by using an autonomous underwater vehicle (AUV) installed with sensors. Atmospheric CO2 above the leakage area was observed by using a CO2 analyzer that was attached to the bow of ship of 50 cm above the sea-surface. The behavior of the leaked CO2 is highly dependent on the tidal periodicity (low tide or high tide) during the CO2 gas release period. At low tide, the pH in sediment and overlying seawater decreased due to strong eruption of CO2 gas bubbles, and the CO2 ascended to sea-surface quickly with a little dissolution to seawater and dispersed into the atmosphere. On the other hand, the CO2 bubbles release was lower at high tide due to higher water pressure, and slight low pH seawater and high atmospheric CO2 were detected. After stopping CO2 gas injection, no remarkable variations of pH in sediment and overlying water column were observed for three months. This is a publication in QICS Special Issue - International Journal of Greenhouse Gas Control, Kiminori Shitashima et. al. Doi: 10.1016/j.ijggc.2014.12.011.

海底地质构造中的碳捕获与封存（海底CCS）目前被视为缓解大气中人为CO2累积的现实可行方案。在实施海底CCS过程中，监测封存CO2对海洋环境的影响至关重要。首次受控CO2释放实验——量化与监测地质碳储存潜在生态系统影响的实验（QICS），于2012年5月至9月在奥班的阿德穆奇尼斯湾进行。我们在QICS实验中应用了原位pH/pCO2传感器，以检测和监测泄漏的CO2，并进行了多项观测。有线实时传感器被部署在CO2泄漏（冒泡）区域附近，海底上方原位pH和pCO2的波动在陆地容器内进行监测。长期传感器被放置在三个不同的观测区的海底。沉积物pH传感器被插入到CO2泄漏区域附近海底下方50厘米的沉积物中。利用安装有传感器的自主水下航行器（AUV）在CO2泄漏区域周围的水柱中进行了pH和pCO2的广域测绘调查。通过连接在船艏50厘米处的CO2分析仪，观测了泄漏区域上方的大气CO2。泄漏CO2的行为高度依赖于CO2气体释放期间的潮汐周期（低潮或高潮）。在低潮期间，由于CO2气体泡强烈喷发，沉积物和上层海水中的pH值下降，CO2迅速上升至海面，与海水溶解度较低并扩散至大气中。另一方面，由于水位较高，高潮期间CO2气泡释放量较低，检测到轻微低pH的海水和较高的大气CO2。在停止CO2气体注入后，三个月内沉积物和上层水柱中的pH值没有观察到显著变化。这是一篇发表在QICS特刊——《国际温室气体控制杂志》上的论文，作者为Shitashima Kiminori等。DOI：10.1016/j.ijggc.2014.12.011。