Laura Chiaramonte

Geomechanical behavior of the reservoir and caprock system at the In Salah CO2 storage project

Significance In Salah is one of the largest carbon capture and storage projects to date and has played a central role in demonstrating the feasibility of onshore sequestration of CO2 in deep saline aquifers. The unique field experience at In Salah provides a valuable case study in managing commercial-scale CO2 injections. In particular, the current work highlights the importance of geomechanics and integrated monitoring in understanding field behavior and managing storage risk. Almost 4 million metric tons of CO2 were injected at the In Salah CO2 storage site between 2004 and 2011. Storage integrity at the site is provided by a 950-m-thick caprock that sits above the injection interval. This caprock consists of a number of low-permeability units that work together to limit vertical fluid migration. These are grouped into main caprock units, providing the primary seal, and lower caprock units, providing an additional buffer and some secondary storage capacity. Monitoring observations at the site indirectly suggest that pressure, and probably CO2, have migrated upward into the lower portion of the caprock. Although there are no indications that the overall storage integrity has been compromised, these observations raise interesting questions about the geomechanical behavior of the system. Several hypotheses have been put forward to explain the measured pressure, seismic, and surface deformation behavior. These include fault leakage, flow through preexisting fractures, and the possibility that injection pressures induced hydraulic fractures. This work evaluates these hypotheses in light of the available data. We suggest that the simplest and most likely explanation for the observations is that a portion of the lower caprock was hydrofractured, although interaction with preexisting fractures may have played a significant role. There are no indications, however, that the overall storage complex has been compromised, and several independent data sets demonstrate that CO2 is contained in the confinement zone.

Analysis of fault leakage from Leroy underground natural gas storage facility, Wyoming, USA

Leroy natural-gas storage site is an anticlinal, fault-bounded, aquifer-storage system located in Wyoming, USA. Based on its abundant data, uncontrolled leakage history and subsequent control by the facility operators, a modeling framework was developed for studying reservoir behavior, examining pressure and gas-inventory histories, as well as gas and brine leakage, and evaluating the sensitivity of that behavior to uncertainty about reservoir properties. A three-dimensional model capturing the bounding fault, layered geologic stratigraphy, and surface topography was calibrated by history data of reservoir pressure and gas inventory. The calibrated model predicted gas arrival at the ground surface that was consistent with the timing of observed gas bubbling into a creek. A global sensitivity analysis was performed to examine the parameters influencing fault leakage, and a geomechanical stability analysis was conducted to investigate the likelihood of fault reactivation. In general, it is shown that a discrete leakage pathway is required to explain the observed gas leakage and its subsequent operational control by reducing reservoir pressures. Specifically, the results indicate that fault leakage is a plausible explanation for the observed gas leakage. The results are relevant to other natural-gas storage sites, as well as other subsurface storage applications of buoyant fluids, such as CO2.RésuméLe site de stockage de gaz naturel de Leroy est un système aquifère dans un anticlinal bordé par faille, localisé dans le Wyoming, USA. A partir de données historiques abondantes sur les fuites non contrôlées et des contrôles postérieurs par les opérateurs de l’installation, un modèle conceptuel cadre a été développé pour étudier le comportement du réservoir, en examinant les séries chronologiques de pression et de réserves de gaz, ainsi que les fuites de gaz et de saumure et en évaluant la sensibilité des réponses aux incertitudes sur les propriétés du réservoir. Un modèle tridimensionnel incluant la faille bordière, la stratification géologique et la surface topographique a été calibré avec les données historiques des pressions et réserves de gaz du réservoir. Le modèle calibré prédisant l’arrivée du gaz à la surface du sol est conforme au temps de dégagement gazeux observé dans un ruisseau. Une analyse globale de sensibilité a été effectuée pour examiner les paramètres influençant la fuite par la faille, et une analyse de stabilité géomécanique a été réalisée pour étudier la probabilité de la réactivation de la faille. De manière générale, on a montré qu’un passage distinct est nécessaire pour expliquer la fuite de gaz observée et son contrôle opérationnel ultérieur par la diminution des pressions dans le réservoir. En particulier, les résultats indiquent que la fuite par la faille est une explication plausible de la perte de gaz observée. Les résultats sont applicables à d’autres sites de stockage de gaz naturel, ainsi qu’à des applications de stockage en sub-surface de fluides volatils, tels que le CO2.ResumenEl sitio de almacenamiento de gas natural de Leroy es un sistema de almacenamiento acuífero anticlinal limitado por falla, localizado en Wyoming, EEUU. Basados en abundantes datos de su historia de filtraciones no controladas y el subsecuente control por los operarios de la instalación se desarrolló un esquema de modelado para estudiar el comportamiento del reservorio, examinando la historia e inventario de las presiones de gas, así como de las filtraciones de gas y de salmuera, y para evaluar la sensibilidad de aquel comportamiento con respecto de las incertidumbres de las propiedades del reservorio. Se calibró un modelo tridimensional que abarca el contorno de la falla, la estratigrafía geológica en capas y la superficie topográfica mediante los datos históricos de la presión y el inventario de gas del reservorio. El modelo calibrado predijo el arribo del gas a la superficie del terreno que fue consistente con el tiempo del burbujeo de gas observado en un arroyo. Se realizó un análisis de sensibilidad global para examinar los parámetros que influyen en la filtración en la falla, y se llevó a cabo un análisis de estabilidad geomecánica para investigar la probabilidad de la reactivación de la falla. En general, se muestra que se requiere una trayectoria discontinua para explicar la filtración de gas observada y su subsecuente control operacional mediante la reducción de las presiones del reservorio. Específicamente, los resultados indican que la filtración es una explicación plausible para la pérdida de gas observada. Los resultados son relevantes respecto de otros sitios de almacenamiento de gas natural, así como para otras aplicaciones de almacenamientos subsuperficiales de fluidos flotantes, tal como el CO2.摘要Leroy地下天然气储藏库是位于美国怀俄明州的一个背斜式的以断层为西边界的含水层储气系统。基于其详细的操作,泄漏及随后的控制历史数据,我们创建了一个模型体系来研究气库状态,模拟压力和库存气量的历史以及气和水的泄漏,并且评估气库状态对地质水文参数的敏感性。其中三维气体运移模型囊括了储气库的边界断层,地层结构和表面地形。储气库的压力和储存量历史数据用来校正这个三维模型。运用校正后的模型预测得到的通过断层泄漏到地表的气量和时间符合观测数据。全局敏感性分析评估了各种气库参数对断层气体泄漏的影响。地质力学稳定性分析对断层重新激活进行了风险评价。我们的研究表明通过断层泄漏的机制解释了Leroy储气库的泄漏以及随后的减压控制历史。本文的研究结果对其他相关地下储气库,比如CO2地质储藏研究有重要的借鉴作用.ResumoO local de armazenamento de gás natural de Leroy é um sistema de aquífero-armazém num anticlinal, limitado por falhas, localizado em Wyoming, EUA. Com base em dados abundantes, no historial da percolação não controlada e no subsequente controlo pelos operadores da estrutura, foi desenvolvida uma rede de modelos para estudar o comportamento do reservatório, examinando o inventário dos dados históricos da pressão e do gás, bem como a percolação de gás e salmouras, e avaliando a sensibilidade deste comportamento com a incerteza sobre as propriedades do reservatório. Um modelo tridimensional englobando as falhas de fronteira, a estratigrafia das camadas geológicas e a superfície topográfica foi calibrado com base nos dados históricos da pressão no reservatório e do inventário de gás. O modelo calibrado previu uma chegada de gás à superfície do solo consistente com os tempos observados da presença de bolhas de gás num pequeno ribeiro. Foi realizada uma análise de sensibilidade global para examinar os parâmetros que influenciam a percolação nas falhas e foi efetuada uma análise da estabilidade geomecânica para investigar a probabilidade de reativação das falhas. Em geral, é demostrado que é necessária uma via de percolação discreta para explicar a fuga de gás e o seu subsequente controlo operacional por redução de pressão no reservatório. Especificamente, os resultados indicam que a percolação através da falha é uma explicação plausível para a fuga de gás observada. Os resultados são relevantes para outros locais de armazenamento de gás natural, bem como para outras aplicações de armazenamento subterrâneo de fluidos flutuantes, tais como o CO2.