In many underground injection control operations, injection allocations across the reservoir interval are not measured and thus are unknown. This is further complicated for a fluid like supercritical carbon dioxide (CO2) because injectivity is expected to vary significantly over time due to reservoir dynamics like pressure cycling and salt precipitation. If anything, these dynamics place a higher priority on storage operators measuring CO2 injectivity at the highest possible spatial resolution. This allows plume models to be optimally history-matched with time-lapse seismic imaging. The result is higher confidence in forecasting plume migration during and after injection operations.

Over the past 15 years, the oil and gas industry has seen the rapid adoption of fiber optic sensing for downhole monitoring of distributed temperature and acoustic sensors along the entire wellbore for a wide variety of production and injection applications. Fiber optic cables installed behind casing or on tubing, along with injection and tubing pressure and temperature gauges, provide crucial downhole data about the reservoir dynamics. In unconventional wells, fluids and proppants were pumped in stages without any feedback about conformity or stimulated reservoir volume. This raised questions about where oil and gas production was really coming from. In recent years, fiber optic sensing has “turned on the lights” downhole. Its real-time analysis now advises on stimulation operations down to the perforation cluster interval, improving our understanding of where oil and gas are produced.

Wells Deploying Fiber Optics for Field-Scale Monitoring
The carbon capture, utilization, and storage (CCUS) industry has begun deploying fiber optic sensing in Class VI wells for measuring, reporting, and verification (MRV) of mechanical integrity testing and vertical seismic profiling (VSP). VSP provides time-lapsed images of the CO2 plume developing in the subsurface. Ideally, time-lapse VSP imaging should be calibrated with CO2 volumetrics. Without fiber optics, operators have limited sensing capabilities across the reservoir interval and require periodic interventions to evaluate well integrity. Certain unconventional and CCUS wells use similar perforated cased hole completions across the reservoir intervals. An opportunity exists to leverage the learning curve from unconventionals and quantify CO2 injection allocations down to the perforation cluster to help improve CCUS injection control operations and time-lapse VSP imaging of the CO2 plume.

Cluster Characterization Addresses Gaps
However, a significant gap exists in MRV: the measurement of supercritical CO2 flow at the scale of the perforation cluster. In both research and practice, we still do not have the full picture of how CO2 is being dynamically allocated in CCUS wells during injection operations. Injection intervals can span hundreds to thousands of feet. This adds a layer of complexity when we try to determine where and how much CO2 is being injected into which formation and when. While injection logging provides some insights, they are only periodic snapshots and can alias temporal reservoir dynamics.

Halliburton Jet Research Center in Alvarado, Texas includes perforation laboratories that are effectively at-scale, physical reservoir simulators for understanding production and injection operations. Studies are routinely performed to optimize the perforation designs to help maximize injection or production from a specific formation. This leads to an optimized design of service for in-field perforating operations and improved well productivity. Instrumentation for acoustic-based injectivity monitoring with distributed acoustic sensing (DAS) further augments those simulations to understand CO2 injectivity at reservoir temperature and pressure. We can develop unique relationships between the acoustic responses and supercritical fluid flow rates from well to formation via perforations at different pressures and temperatures.

Lab to the Field
Learning from unconventionals, fiber optic sensing can turn on the lights for CCUS and quantify CO2 injection allocations. We can now perform at-scale simulations in the perforation laboratory to determine the expected acoustic responses for specific reservoirs, perforating designs, and injection operations. We can understand the acoustic response to individual CCUS operations a priori. When implemented in VISUM, our real-time downhole analysis software, this accelerated learning curve helps to deliver quantification of CO2 injection allocations at the perforation interval from the start-up of injection operations. This reduces the need for in-situ calibration with intervention operations. The improved understanding of reservoir dynamics helps improve our understanding of plume development and migration by calibrating time-lapse VSP images with CO2 volumetrics.

To learn more about how Halliburton helps companies overcome CCUS challenges, visit www.halliburton.com/CCUS.

Author:
Dr. Glenn Wilson, Head of Measurement,
Reporting & Verification, Low Carbon Solutions

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