A Fit-For-Purpose Workflow for In-Situ Stress Characterization in Carbon Capture and Storage Formations
Authors: Wydiabhakti T. B. , Hati S. , Das B. , Kumar A. , Thorat A. , Singh A. , Sherratt P. J. 
Published: October 2023

The efficiency of carbon capture and storage (CCS) methodology highly depends on the in-situ stress characterization of the storage cavities to prevent the leakage. The injection pressure must be optimized and be in line with the in-situ stresses and reservoir storativity. The objective of this paper is to characterize stress regime, magnitudes, and direction, using the integrated stress analysis approach, acoustics, image, and caliper data, and later validated using the independent stress testing analysis.

The integrated workflow starts with estimating stress magnitudes by modeling stress sensitivity to acoustic waves in anisotropic formations, making use of the axial, radial, and azimuthal waveforms. This is followed by multiarm caliper and image analysis, which leads to estimating the stress regime and direction. Dynamic stress tests were conducted, which provided the calibration data for minimum horizontal stresses. To further validate the accuracy, pre- and post-stress test image logs were analyzed, providing the necessary validation to the entire workflow.

Borehole acoustics tools are capable of recording axial, radial, and azimuthal waveforms, thereby characterizing the near-wellbore as well as the far-field environment. Stress concentrations around the borehole lead to radial shear slowness variation. Estimation of stress magnitudes is possible by modeling the stress sensitivity to acoustic waves in the anisotropic sandstone bodies. Multiarm caliper and image analysis yield information about stress regime and direction.

Recent years saw an increased interest in acoustics geomechanics for geological carbon dioxide (CO2) storage, to understand the potential of caprock to trap CO2. Mohr’s coulomb, uniaxial strain, and poroelastic stress method played a key role in estimating the horizontal stress magnitude, which were further validated by leakoff tests, formation integrity tests, and microfracturing results.

This workflow highlights the integration of acoustic radial profiling and image logging for microfracture depth selection, which resulted in increased efficiency of the stress test by 30%. These were also validated using the image and acoustic logs to understand the prefracture and post-fracture anisotropy mechanism.

The workflow combines the various domain processes involved in reservoir characterization to create a fit-for-purpose workflow. Hence, the workflow not only characterizes the entire process, but also highlights the key integration points required for a higher and optimized operational efficiency. The prefracture and post-fracture image logs were compared to increase the confidence of microfracture results.

A unique amalgamation of advanced acoustic, image, and formation testing workflows has been demonstrated, opening new ways of collaboration between several types of formation logs and data for accurate and detailed horizontal stress characterization.

This paves the way for reliable estimates of the maximum horizontal stress magnitudes, which otherwise remain a challenge in the industry. The workflow demonstrates the much-required integration between different domains and logging data, for complete characterization of formation zones required for CCS.