A Novel Integration of Advanced Acoustic Geomechanics and Reservoir Micro Fracturing Techniques for Refined Stress Characterization in Carbon Capture and Storage Formations
Authors: Kumar A. , Wydiabhakti T. B. , Singh A. , Hati S. , Das B. , Thorat A. 
Published: November 2023

CCUS projects are gaining momentum as organizations are moving towards carbon net zero. The success of CCUS operations relies on the in-situ rock characterization for efficient carbon storage. As part of this novel integrated approach, we aim to identify stress regimes, stress magnitudes, and direction. In this integrated approach, we characterized in-situ stress using log measurements such as acoustics, image, caliper data, and microfracturing analysis.

The integrated workflow characterizes the near-wellbore and far-field environment by analyzing axial, radial, and azimuthal waveforms recorded by borehole acoustics tools. Radial shear slowness variation indicates stress concentrations around the borehole, enabling estimating stress magnitudes in anisotropic sandstone bodies. Multi-arm caliper and image analysis provide insights into stress regime and direction. Dynamic stress tests are then conducted, providing calibration data for minimum horizontal stresses. Pre- and post-stress test image logs are analyzed to validate the accuracy of the workflow.

Recently, there has been a growing trend of incorporating mechanical earth models (MEM) into assessing carbon dioxide (CO2) storage feasibility. These models play a crucial role in estimating the integrity of the cap rock for CO2 storage and conducting feasibility studies for hydraulic fracturing, aiming to enhance injectivity. Integrating MEM into the workflow enables a comprehensive analysis of the subsurface conditions, leading to informed decisions regarding CO2 storage and hydraulic fracturing operations.

Mohr's Coulomb, uniaxial strain, and poroelastic stress methods greatly influenced the estimation of horizontal stress magnitude. These methods played a crucial role in accurately assessing the level of horizontal stress, which was subsequently confirmed through rigorous leakoff tests, formation integrity tests, and analysis of microfracturing results.

By integrating various domain processes involved in reservoir characterization, the workflow is designed to be tailored to the specific needs of the task. This comprehensive approach not only characterizes the process but also emphasizes the essential integration points necessary for achieving higher operational efficiency. To enhance the confidence in microfracture results, a comparison between pre-fracture and post-fracture image logs is conducted, further strengthening the reliability and accuracy of the findings.

Demonstrating a novel combination of advanced acoustic, image, and formation testing workflows has introduced innovative avenues for collaboration among various types of formation logs and data, enabling accurate and detailed characterization of horizontal stress. This breakthrough lays the foundation for obtaining dependable estimates of maximum horizontal stress magnitudes, addressing a persistent challenge in the industry. The workflow exemplifies the vital integration between different domains and logging data, enabling a comprehensive characterization of formation zones essential for carbon capture and storage (CCS) purposes.