Single-well experimental design for studying residual trapping of supercritical carbon dioxide

Abstract

The objective of our research is to design a single-well injection withdrawal test to evaluate residual phase trapping at potential CO 2 geological storage sites. Given the significant depths targeted for CO 2 storage and the resulting high costs associated with drilling to those depths, it is attractive to develop a single well test that can provide data to assess reservoir properties and reduce uncertainties in the appraisal phase of site investigation. The main challenges in a single-well test design include (1) difficulty in quantifying the amount of CO 2 that has dissolved into brine or migrated away from the borehole; (2) non-uniqueness and uncertainty in the estimate of the residual gas saturation (S gr ) due to correlations among various parameters; and (3)the potential biased S gr estimate due to unaccounted heterogeneity of the geological medium. To address each of these challenges, we propose (1) to use a physical-based model to simulation test sequence and inverse modeling to analyze data information content and to quantify uncertainty; (2) to jointly use multiple data types generated from different kinds of tests to constrain the S gr estimate; and (3) to reduce the sensitivity of the designed tests to geological heterogeneity by conducting the same test sequence in both a water-saturated system and a system with residual gas saturation. To perform the design calculation, we build a synthetic model and conduct a formal analysis for sensitivity and uncertain quantification. Both parametric uncertainty and geological uncertainty are considered in the analysis. Results show (1) uncertainty in the estimation of S gr can be reduced by jointly using multiple data types and repeated tests; and (2) geological uncertainty is essential and needs to be accounted for in the estimation of S gr and its uncertainty. The proposed methodology is applied to the design of a CO 2 injection test at CO2CRC's Otway Project Site, Victoria, Australia. Introduction and ObjectiveThe geologic sequestration of anthropogenic greenhouse gases to mitigate climate change is receiving increasing attention as a means to reduce atmospheric emissions and the related impacts as a result of continued use of fossil fuels. The ability of a host formation to effectively trap CO 2 determines the suitability of a proposed site for long-term CO 2 sequestration. Four trapping mechanisms have been identified (IPCC, 2005): structural trapping, residual phase trapping, solubility trapping and mineralization trapping. This study focuses on residual phase trapping, i.e., the immobilization of individual bubbles or relatively small blobs of the CO 2 -rich phase. TheCO 2 bubbles are either trapped by capillary forces or are stuck in local trapping structures or dead-end portions of the pore space, preventing further CO 2 migration in response to pressure gradients or buoyancy forces. (CO 2 saturation can be reduced below the residual value by processes other than viscous flow, e.g., by compression or dissolution.) A parameter referred to as re...

Residual CO2 saturation estimate using noble gas tracers in a single-well field test: The CO2CRC Otway project

“…3 shows a schematic of the Otway residual saturation and dissolution test sequence. The field experiments roughly followed the procedure discussed in Zhang et al (2011), though there were differences in parameters such as injection rates and times because of field constraints.…”

“…Two noble gases, krypton (Kr) and xenon (Xe), comprise a critical component in the conceptional design of the Otway SWTT (Zhang et al, 2011). For the SWTT, a U-tube assembly was used to collect suitable fluid samples from the CRC-2 well.…”

iTOUGH2: A multiphysics simulation-optimization framework for analyzing subsurface systems

“…They must be determined iteratively by an analysis of the final residuals after a preliminary inversion. Alternatively, through proper scaling of the objective functions in iTOUGH2, these statistical parameters may be jointly estimated along with the adjustable parameters of the physical system, as demonstrated in Finsterle and Zhang (2011b). It is recommended to perform a detailed residual analysis after an inversion to test whether the final residuals comply with the assumptions underlying the chosen objective function.…”

“…A number of statistical tools supporting the residual analysis are implemented in iTOUGH2; they include scatter plots, a runs statistics, covariance matrices of the model prediction and residuals, statistical outlier identification, local reliability measures, and the relative contribution to the objective function. These residual statistics are discussed in Finsterle andZhang (2011b). Reproducing the observed system response at the calibration points is a necessary but not sufficient condition for a successful inversion.…”

Comparison of surface and near-surface geochemical methods for detection of gas microseepage from carbon dioxide sequestration

“…Coupling with geochemical models will allow the prediction of dissolution of primary minerals and precipitation of secondary minerals at the advancing front and within the plume (Liu and Illangasekare, 2008;Samper et al, 2009;Zhang et al, 2010). Three-dimensional seismic surveys can provide an image of the reservoir prior to injection, selected time intervals during the CO 2 injection phase (4-D), and post-injection monitoring (Benson, 2010).…”