Julie Kowan, Luis Berrizbeitia, Marius Tjengdrawira, Jianyong Pei, Baker Hughes
Data requirements for proper site characterization and Class VI EPA permitting for CCUS operations are extensive. The need for a rich data set is somewhat intuitive, as it is imperative that the subsurface geology and geomechanics are well understood to ensure caprock integrity and CO₂ containment. However, some sites currently under evaluation for underground CO₂ storage are lacking key data required to fully assess the suitability of the site for such a purpose. One such site is in central California, where the only offset well data available to the operator was from legacy wells available via a public database. A pre-feasibility study using publicly sourced data indicated the site is a good candidate for CO₂ injection and storage (Bynum, AAPG CCUS 2022 abstract reference #12027613) and a characterization well is planned to obtain the necessary data to fully evaluate the site’s storage capacity.
This study was designed primarily to de-risk the characterization well, beginning with the construction of a geomechanical model using drilling and logging data from 2 of the nearby offset wells with relatively better data sets compared to the others available publicly. Despite the data limitations, a good match of predicted to observed failure was obtained, indicating the model is likely reasonable. The next step was to perform a wellbore stability analysis to determine the range of mud weight (MW) necessary to prevent excessive wellbore collapse and avoid lost circulation in the planned characterization well. Two MW profiles were created, a less conservative MW profile meant to maintain wellbore stability and a more conservative MW profile meant to limit borehole rugosity in order to maximize log quality and data acquisition. A Quantitative Risk Analysis (QRA) was also run to address how uncertainties in the input parameters, such as pore pressure, stresses and rock properties impact the optimal MW and casing placement and to inform data collection recommendations.
The outcome of the geomechanical modeling and wellbore stability analysis were then utilized to perform a RiskGuard™ assessment, a multi-discipline risk management process that used to develop customized solutions to address the risks and hazards identified for the planned characterization well. This risk assessment was focused on the drilling phase, but also looked forward to the eventual application for a Class VI permit from the EPA and injection of CO₂, especially with regard to the data collection recommendations. Drilling risks identified included the possibility of drilling through reactive or weakly bedded formations and low leak-off at the surface casing shoe limiting the MW in the next hole section. Risks identified applicable to the injection phase included the presences of natural fractures in the storage reservoir and fault reactivation. This presentation highlights the value of a geomechanics-based risk assessment for CCUS applications and will review the data limitations, geomechanical model, risk assessment (risks and mitigation measures) and data collection recommendations for this potential CCUS site.