Graduate student Andrew Duguid has completed his study of the attack of cements by carbonated brines and will defend his thesis in the summer. His data on cement decomposition have been provided to Bill Carey at Los Alamos and to Jim Johnson at Lawrence Livermore Lab, who will reproduce his results using their simulations and thereby refine their reaction rate parameters for cement constituents.
The team will also assess the importance of pressure on the corrosion rate of cement as results from the high-pressure studies at NETL become available. The NETL results will be compared to predictions from the LANL and LLNL models and the geochemical module of Dynaflow. If necessary, improved pressure dependence will be introduced into Dynaflow.
A new graduate student will also join the team in September, 2006, to study the transport and mechanical properties of cement subjected to attack by carbonated brine. Duguid’s results indicate a catastrophic loss of integrity of the cements when the corrosion is well advanced. However, there may be a more subtle deterioration that occurs in limestone formations, where our short-term (i.e., 1-year) experiments indicate little or no attack, that might have significant impact on leakage over the course of a century. We will use NMR to measure diffusion coefficients and a variety of techniques to measure permeability changes during leaching. We will also study the change in strength and stiffness as corrosion proceeds. This information will be needed to refine the leakage model and expand our confidence regarding the risk of leakage over the long term.
Following a visit to CMI by Tony Hayward, BP has mobilized a team to acquaint us with BP’s field experience regarding durability of cement exposed to carbon dioxide, and to obtain samples of cement from wells. If the latter effort is successful, we will study their microstructure and composition, and subject them directly to corrosion testing to see how they compare to our home-made samples. This will provide the first systematic data regarding features of the structure and/or chemistry of samples subjected to long term aging at elevated temperature and pressure, and thereby enable us to refine our predictions of risk.
The direction of the experimental program beyond Year 7 will depend on availability of cement samples and field data for leakage rates from wells. Field samples, if available, will be used for direct tests of corrosion rate, as well as transport and mechanical properties. If we obtain field data regarding methane leakage rates, those results will be used to infer the size of annuli that are likely to be present in sealed wells and provide initial conditions for the simulations of corrosion of cement.