An Innovative and Tailor Made Stress Testing Workflow for CCS Formations
Authors: Wydiabhakti Tety Benedicta , Kumar Arvind , Lopes Velerian S. 
Published: February 2024

Carbon capture and storage (CCS) has become a critical strategy for mitigating carbon emissions and achieving environmental sustainability. In-situ stress determination plays a pivotal role in the success of Carbon Capture and Storage (CCS) initiatives. It is a fundamental component of ensuring the safe and reliable containment of captured carbon dioxide within underground storage reservoirs by enhancing the integrity and stability of reservoirs, minimizing the risk of potential leakage, and optimizing the placement and design of new CO2 injection wells. In summary, in-situ stress determination serves as the cornerstone of secure and effective CCS operations, underlining the critical importance of comprehensive geomechanical assessments for a sustainable carbon reduction strategy.

In this integrated approach, we conduct comprehensive stress testing measurements and integrate them with various openhole log measurements, including acoustics, imaging, caliper data, geomechanical analysis. The integrated workflow is designed to assess both the near-wellbore and far-field environment by analyzing axial, radial, and azimuthal waveforms recorded by borehole acoustics tools. Notably, variations in radial shear slowness serve as indicators of stress concentrations around the borehole, allowing for the estimation of stress magnitudes within anisotropic sandstone bodies. Multi-arm caliper and image analysis are crucial components of the stress testing process, providing insights into stress regime and direction. To further refine our stress testing, dynamic stress tests were conducted, offering valuable calibration data for minimum horizontal stress estimation. The accuracy of our workflow is validated through the analysis of pre- and post-stress test image logs.

In recent times, there has been a growing trend in incorporating mechanical earth models (MEM) into the assessment of carbon dioxide (CO2) storage feasibility. These models play a pivotal role in estimating the integrity of the cap rock for CO2 storage and conducting feasibility studies for hydraulic fracturing to enhance injectivity. The integration of MEM into our workflow facilitates a comprehensive analysis of subsurface conditions, enabling informed decisions regarding CO2 storage and hydraulic fracturing operations. These methods are instrumental in accurately assessing the level of horizontal stress, a verification process that involves rigorous leakoff tests, formation integrity tests, and an analysis of microfracturing results.

This study highlights the significant potential of this integrated approach for in-situ stress characterization in CCS formations. It not only contributes to safer and more efficient carbon storage but also offers a foundation for informed decisions regarding wellbore stability and hydraulic fracturing operations, critical elements in the success of CCS initiatives. Ultimately, the integration of stress testing with acoustic logs, borehole image logs, and geomechanical models represents a robust strategy for achieving a comprehensive understanding of subsurface stress, addressing a fundamental aspect of CCS implementation.