Hydrogeochemical dynamics of natural carbon dioxide fields: Analogs for geological carbon storage and constraints on convective dissolution

只有当二氧化碳在深层地质构造中保存数千年，地质二氧化碳储存才能用于减少二氧化碳的排放。不幸的是，沉积盆地中的自由相二氧化碳密度低于地层水，因此二氧化碳从这些储层渗漏回地表是一个主要问题。然而，随着时间的推移，二氧化碳溶解到地层水中，增加了水的密度。溶解的二氧化碳随后会下沉到沉积盆地的较深部分，并且不太可能再次浮出水面。二氧化碳溶解得越快，就能越早安全地储存起来。该项目将在两个尺度上评估二氧化碳的溶解情况：(1)利用新墨西哥州一个名为Bravo Dome的大型天然二氧化碳储层的地质和地球化学记录，估计二氧化碳在地质时间尺度上的溶解速度和天然二氧化碳捕集器的紧密程度；(2)本研究还将为溶解二氧化碳的运输建立按比例的实验室模型，以确定二氧化碳的总体溶解速率。溶解的二氧化碳电流的空间结构将用x射线断层扫描成像。这些实验将用于校准一个动态模型，然后该模型可用于模拟实验室观测结果，并解释观测到的现场数据，以限制长时间内二氧化碳的溶解和封存速率。该项目将流体力学、地质学和地球化学结合在一起，并将提供实地二氧化碳溶解速率的初步估计，为有关地质二氧化碳储存长期安全性的辩论提供信息。实验研究将解决由于密度差异导致的溶质迁移的几个基本问题，这些问题对地下水侵入地热能的一系列广泛问题有影响。将要开发的模型将捕捉这些过程的基本物理特性。这些模型的发展是实现地质CO2储存不确定性量化的关键。

Geological carbon dioxide storage can be used to reduce carbon dioxide emissions only if the carbon dioxide remains in deep geological formations for thousands of years. Unfortunately free-phase carbon dioxide in sedimentary basins is less dense than the formation water and therefore leakage of carbon dioxide from these storage reservoirs back to the surface is a major concern. Over time, however, carbon dioxide dissolves into formation waters and increases the water density. Dissolved carbon dioxide will then sink to deeper parts of the sedimentary basins and it is very unlikely to surface again. The faster carbon dioxide dissolves the sooner it is stored safely. This project will evaluate the dissolution of CO2 on two scales: (1) The geological and geochemical record of a large natural carbon dioxide reservoir called Bravo Dome in New Mexico will be used estimate how fast carbon dioxide has dissolved on the geologic timescale and how tight the natural CO2 trap has been; (2) This study will also build scaled laboratory models for the transport of the dissolved carbon dioxide that determine the overall rate of carbon dioxide dissolution. The spatial structure of the dissolved carbon dioxide currents will be imaged with x-ray tomography. The experiments will be used to calibrate a dynamic model that can then be used to model laboratory observations and to interpret the observed field data to constrain the dissolution and sequestration rates for CO2 over long time.This project brings together fluid mechanics, geology, and geochemistry and will provide a first estimate of carbon dioxide dissolution rates in the field, to inform the debate about the long-term safety of geological carbon dioxide storage. The experimental study will address several fundamental questions about the migration of solutes due to density differences that have implications for a broad set of questions for salt-water intrusion to geothermal energy. The models that will be developed will capture the essential physics of these processes. The development of such models is key to enable uncertainty quantification in geological CO2 storage.