Ninth Year Annual Report:
Carbon Storage: Future Plans
In the experimental study of cement corrosion, the Scherer-Prevost Group will extend their examination of the influence of concentrations of CO2 and calcium on the rate of attack. The researchers will characterize the pore structure and diffusivity of the gel layer, using nitrogen sorption, environmental scanning electron microscopy, and (in collaboration with Dr. Leo Pel in Eindhoven) NMR. To identify the most significant range of parameters for these experiments, the team is collaborating with Dr. Bruno Huet (Schlumberger). In turn, their data are being used to refine the predictions of his module, which is a module for Dynaflow.
Jean Prévost is continuing development of the flash calculations continues in collaboration with Lee Chin (ConocoPhillips). It is now possible to simulate the phase changes as carbonated brine rises through a leaky well, so a simulation of flow in an annulus will be undertaken as soon as a new post-doc arrives. That calculation will be refined as the experimental results on transport and mechanical properties of the corroded material become available.
The Celia group is working to combine numerical and analytical solutions more generally within a given simulation. Their current challenge is to include diffuse leakage across caprock formations. While this can be done for the analytical and numerical solutions individually, their coupling is an interesting challenge. The researchers' overall philosophy is to use a more detailed numerical model for the injection formation, and to represent the leakage patterns and profiles in other permeable layers (and along wells) using the semi-analytical framework. The group will also continue to develop a program focused on brine management. This work addresses possible pressure control within a formation, and relates to important questions about limits on injectivity imposed by fracture pressure constraints and the general question of where the displaced brine goes.
Quantifying the Kinetics of CO2 Hydrate Formation
The thermodynamics of CO2 hydrates, while important, constitutes only one part of the picture. Another crucial aspect of this problem is the kinetics of hydrate formation. Understanding the formation of the critical hydrate nucleus, and its structural and dynamic characteristics are of primary importance. Experimental studies of this phenomenon are hindered due to the inability of current techniques to access the nanoscopic time and lengthscales involved in the nucleation and growth process.
In principle, molecular dynamics is well-suited to tackle this challenge. However, the formation of a nucleus is a rare event and therefore, the waiting time for observing the formation of a critical nucleus within the typical ~103 nm3 systems used in molecular dynamics can be longer than the nanosecond time scale, thereby making it computationally challenging even with the current computer infrastructure.
In recent years, several advanced techniques have been proposed to enable sampling of rare events through molecular-based simulations. These techniques have been used successfully to model various complex phenomena such as salt dissociation in water, ice formation, and protein folding. The researchers aim to implement concepts of these advanced sampling techniques to study CO2 hydrate formation over broad ranges of temperature, pressure and salinity. This will enable them to identify the characteristics of the critical nucleus for CO2 hydrate formation and estimate the associated nucleation rates under conditions relevant to carbon capture and storage. These studies will then be extended to evaluate the effect of confinement on kinetics of CO2 hydrate formation.
Quantifying CO2 Hydrate Stability in Confinement
Previous studies of confinement-induced clathrate inhibition clearly indicate that the dissociation of hydrates is moved to lower temperatures or higher pressures relative to bulk conditions, but we are clearly far from developing a comprehensive picture of clathrate inhibition in mesopores. Experimental studies have been challenging due to difficulty in attaining thermal equilibrium, and because of hysteresis between hydrate formation and dissociation in confinement.
In addition to providing a detailed picture of clathrate behavior in confined systems, molecular simulations also enable systematic investigation of the effects of various parameters such as pore geometry and strength of pore-water interaction (which will modify how water wets the pore surface) on observed clathrate inhibition. Molecular simulations also provide a valuable tool to bridge microscopic behavior to observed macroscopic phenomena. For example, it will be of fundamental importance to explore the correlation between the changes in water behavior in the vicinity of various surfaces and the effect of those surfaces on hydrate stability. The goal of this work is to understand in a systematic way the roles of surface chemistry (hydrophobic, hydrophilic), extent of confinement, and thermodynamic conditions (temperature, pressure) on CO2 hydrate stability under conditions relevant to carbon capture and storage.
Externally Funded Projects
Within the broad CMI Storage Group, a number of new projects have been initiated in the last year. These include projects funded by the Environmental Protection Agency (Celia), the Department of Energy (Celia, Peters, Scherer), and the National Science Foundation (Celia, Peters). The projects complement the ongoing CMI storage activities in many ways, including the following: (1) joint work with EPA on practical models for practitioners including EPA regional offices and EPA personnel who are likely to review applications for CCS operations; (2) Field modeling applications focused on the Illinois Basin and the Michigan Basin; (3) Synthesis of leakage risk modeling with broader subsurface and surface constraints including protection of other subsurface minerals and economic and right-of-way issues associated with surface facilities and transport; (4) continuation of experiments in old wells with a focus on data analysis and automated algorithms; and (5) development of advanced numerical methods to incorporate system complexity.