Injecting carbon dioxide (CO2) into the subsurface comes with the added responsibility of understanding the movement of the CO2 once injected, and ensuring that it remains contained in the target reservoir. Consequently, a significant part of the sequestration process is to build and maintain models of the subsurface that will predict the flow of the injected CO2. These models need to integrate all data available so that the subsurface movement of the CO2 can be predicted should changes to the injection parameters be made. As the CO2 plume is monitored by various measurements, the model needs to be flexible enough to be updated to account for any difference between predicted and known behavior. An integrated predictive reservoir model was created for the Illinois Basin – Decatur Project utilizing a variety of data collected from 2007 until January 2013. The evolution of this model will be discussed. Prior to the beginning of injection, in November 2011, reservoir models and numerical simulations were used extensively to design the wellbore, completions, and well tests; optimize predicted injectivity; simulate the CO2 subsurface migration development and pressure perturbation; analyze and understand well test results; and quantify uncertainties in predictions. Now, with the help of dynamic injection data collected, the calibration of the model has been accomplished by honoring the observations and this facilitates making more informed forecasts. Our analysis indicates a laterally developing CO2 subsurface migration, thus reducing the near to mid‐term expectation of CO2 reaching the seal and upper sections of target reservoir. Further planned modeling efforts include additional model refinements required for anticipated future applications including regulatory compliance and multi‐physics data integration.
The microseismic activity observed in and around a geologic formation undergoing carbon dioxide (CO 2) injection is a combination of natural, or "background", microseismicity plus that activity which is induced by injection operations. Since injection pressure within storage target formations are maintained safely below fracture pressure this induced activity typically originates at natural pre-existing zones of mechanical weakness presented by structural or stratigraphic features. The combination of mechanical properties and in-situ stresses dictate the focal mechanism for microseismic emissions, an understanding of which facilitates the use of observed microseismicity for regulatory compliance and project management. Under favorable conditions microseismic activity may be unambiguously correlated with structural and/or stratigraphic features directly observed in seismic data, thus providing strong constraints to interpretation of observed microseismicity for focal mechanisms. However, in many cases, such as at the Illinois Basin-Decatur Project (IBDP), this direct correlation is elusive and other indirect support is required. Analysis of microseismicity at IBDP has been performed within the context of the integrated reservoir and mechanical earth models developed as part of the site characterization and monitoring program. The IBDP integrated modeling workflow involved continuous and geotechnically consistent data integration for geologic modeling, calibrated flow simulation, three-dimensional (3D) Mechanical Earth Model, and coupled hydromechanical simulation. Using the coupled model, scenario-based forward modeling of microseismicity was performed for hypothetical focal mechanisms inferred from observed data. The experience gained at IBDP illustrates the importance of integrated modeling in the interpretation of microseismic activity for focal mechanisms and provides valuable insights into critical data gaps which could be the target of future basic research efforts.
The Illinois Basin -Decatur Project (IBDP) plans to inject one million tonnes of carbon dioxide (CO 2 ) into the Mt. Simon Formation over a three-year period, starting in late 2011. Uncertainty analyses that were conducted at successive stages of the project have been used to evaluate the impact of additional data on the uncertainty in reservoir performance predictions.Reservoir simulators are predictive tools that help the project team evaluate the injectivity, storage capacity and containment capabilities of a reservoir for carbon capture and storage (CCS) projects. Simulation studies for IBDP started in 2008 using general regional data. Over time, reservoir models have increased in complexity and have become more representative of the Mt. Simon Formation as more data have been acquired.An initial uncertainty analysis used models based on two-dimensional (2D) seismic data and available logs from a nearby well. After drilling the injection and monitoring wells at the storage site, petrophysical measurements were obtained that enabled a detailed sensitivity analysis to identify parameters that are critical to injectivity, CO 2 migration, and corresponding pressure pulse evolution. This information helped reduce the number of uncertain parameters and their ranges for the second uncertainty analysis. Lastly, after gathering three-dimensional (3D) seismic data, results of special core analysis, and injectivity tests, the reservoir model and uncertainty ranges of other input parameters were updated for a final iteration of pre-injection uncertainty analysis.Results of the first uncertainty analysis helped the project team identify an uncertainty envelope of possible CO 2 migration scenarios. The second stage of uncertainty analysis targeted wide ranges in reservoir performance predictions, indicating several reservoir parameters on which to focus additional characterization efforts. A more complete, final round of uncertainty analysis produced manageable ranges of predicted uncertainties and a credible basis of reservoir performance expectations prior to the operational phase of the project. Results of this analysis can be used to identify the area of review (AoR) for permitting, priority and placement of monitoring tools, as well as timing of repeat surveys and scenarios for injection schemes in the near future.
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