Due to significant temperature differences between the injected medium and in situ formation, injection of CO2 (as with water or other cold fluids) at depth induces thermal changes that must be accounted for a complete understanding of the mechanical integrity of the injection/storage system. Based on evaluations for the Northern Lights Carbon Capture and Storage (CCS) project, we focus on thermal effects induced on the caprock via conduction from cooling in the storage sands below. We investigate, using both analytical and numerical approaches, how undrained effects within the low permeability caprock can lead to volumetric contraction differences between the rock framework and the pore fluid which induce both stress and pore pressure changes that must be properly quantified. We show that such undrained effects, while inducing a more complicated response in the stress changes in the caprock, do not necessarily lead to unfavourable tensile conditions, and may, in fact, lead to increases in effective stress. These observations build confidence in the integrity of the caprock/seal system. We also show, through conservative assumptions, that pressure communication between the caprock and storage sands may lead to a localised negative effective stress condition, challenging stability of the base caprock, which will be mitigated for in field development planning.
A fit for purpose 4D Geomechanical model is regarded valuable for most fields. Although tools for building such models have been available for some time they are commonly not made or not fully utilized due to the extensive amount of time, complexity and costs involved. In Equinor a workflow (DE4RM) has been developed for fast 4D geomechanical modeling, effective visualization and interpretation. Using this workflow, models have been built for more than 20 fields over the last 4 years and results applied for a variety of areas including input to seismic time shift analysis, short and long term well planning, estimation of cooling effects from injectors, subsidence/compaction predictions, input to well completion, monitoring optimization, overburden integrity studies, out of zone injection and fault re-activation assessment. Some examples on such use will be given in this paper. On the modeling side key factors for efficient modeling are utilization of existing reservoir models, use of commercial finite element software and a streamlined, easy to use, workflow for all pre-processing steps. Particularly, a well-equipped toolbox for various grid-editing functionality has been essential for being able to complete the modeling fast enough (1-3 weeks). Once a model is built it is readily available for both geomechanical experts and non-specialists through the open source powerful visualization platform Resinsight. In this software geomechanical capabilities have been developed over the last years guided by practical use of the models. Further development on both the modeling, visualization and post-processing side is ongoing and as Resinsight is open source, use of the software and development of new functionality is possible for anyone. In summary, 4D geomechanical modeling and utilization of such models has become a daily activity in Equinor for numerous applications, gradually replacing simplified 1-D based methods with the faster and more accurate DE4RM methodology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.