Protection of Caprock Integrity for Large-Scale CO2 Storage (PROTECT)
Project period2014 – 2017
Goal of the Project:
The goal of the PROTECT project is to better understand the ability of the caprock to safely and effectively contain CO2 in large, industrial-scale storage projects.
- Technical content:
The project will study typical storage environments in the North Sea that have large storage capacity for injected CO2. The project addresses concerns that injection rates of several millions tons per year can overpressurize the storage complex, inducing damaging stress on the caprock and causing unwanted leakage. Possible damage to the caprock includes hydrofracturing, enhancement of an existing fracture network, and/or fault reactivation. In addition, chemical and thermal processes occurring within the system may impact these geomechanical processes. The scientific techniques involved in the project are several fold; (1) analyzing caprock samples to quantify relevant properties; (2) experimenting on samples to understand the impacts of various mechanical, chemical and thermal processes that occur during CO2 injection; (3) developing mathematical models and computer codes to simulate the complex interplay between these processes; (4) applying these codes to real world examples of CO2 injection and the subsequent stress environment.
- Technical advantages:
The PROTECT project emphasizes the integration of data acquisition, experimental and computational studies to advance new knowledge in our understanding of caprock integrity. Investigations are performed both at the small scale, the scale at which the details of processes in individual fractures are resolved (cm to m), and the large scale, the reservoir or basin scale that will require some upscaling (10 m to km). In addition, the integration of different approaches is particularly challenging, requiring a special focus on synthesis of data and simulation through benchmark problems. Given the importance of caprock integrity to stakeholders, a separate area is dedicated to translating the academic results into data, experimental and computational recommendations when assessing and designing storage projects.
- Results to date:
Shear tests on Svalbard shale samples executed. The effect of water on the shear strength of rock is dramatic, the peak strength is reduced to about 50% of the dry sample and the residual strength is close to zero.
Methods utilizing gravimetric and/or EM data in the inversion process have been developed. Key elements in this inversion methodology are structure identification and uncertainty quantification.
New stable and convergent fracture-matrix discretization scheme for flow and rock-mechanical equations has been developed. The method can be solved on non-matching grids and gives more flexibility for modeling fracture-matrix interactions (e.g. discontinuous pressure) as well as including intersecting fractures and dead-end fractures in coupled systems.
Large-scale simulations have been carried out of single-phase fluid injection in the Utsira, which covers a time span of 25 years. The results give the pressure build-up, the expansion of the Utsira formation and the seabed uplift. There is significant capacity for CO2 due to volume expansion of the highly compressible unconsolidated sand. Seabed uplift is nearly entirely due to the expansion of the Utsira sand.