DOE OSTI2018
The In Salah gas development project, initiated in 2004, involves the long-term storage of waste carbon dioxide associated with natural gas production at several central Algerian fields. Rather then vent the extracted CO 2 into the atmosphere the operators, BP, Sonatrach, and Statoil chose to have the gas compressed, dehydrated, transported, and injected into a deep saline aquifer leg of the Krechba gas reservoir (Matheison et al. 2011). For this effort three horizontal state-of-the-art injection wells were drilled to a depth of 1500-1800m, using geo-steering technology to follow the roughly 20m thick reservoir. To maximize the injectivity, the wells were oriented perpendicular to the direction of maximum stress, the dominant fracture direction. Long-term plans were to store up to 17 million tonnes of carbon dioxide during the life of the program (Matheison et al. 2010). The project at In Salah was a pioneering effort in several respects and involved the investment of over 100 million dollars by the member companies. One feature that distinguishes In Salah from several other industrialscale CO 2 sequestration projects, such as Sleipner (Chadwick et al. 2012), Weyburn (White et al. 2011), Decatur (Kaven et al. 2014), and Aquastore (Worth et al. 2014) is the generally smaller storage volume in terms of overall reservoir thickness and lower average porosities of around 15%. With the exception of Weyburn, these other sites are characterized by generally thick sequences of high porosity sandstones. Therefore, one might expect that the pressure buildup near the wells could be larger at In Salah, with consequences for reservoir deformation and caprock strain. The role of fractures in providing storage and increasing reservoir permeability is one factor that would likely impact the pressure distribution around the well. However, the detailed effect of existing fractures on flow was not established prior to the injection at In Salah. The unique features of the In Salah storage site point to the importance of wellbore, geophysical, and geochemical monitoring to ensure that the integrity of the storage complex is maintained both during and after injection. In 2005 a Joint Industry Project (JIP) was set up, in an effort to use various geophysical, geochemical, and production techniques to monitor the fate of the injected carbon dioxide (Matheison et al. 2011). Here in this paper we describe the efforts made to monitoring the fate of the injected carbon dioxide, the state of the caprock, the estimated outcome of the storage effort, and some of the uncertainties that remain.