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The assessment of CO2 storage capacity and long-term time-lapse monitoring is a fundamental criterion for the management of carbon sequestration projects. Pulsed-neutron logging provides an essential method for measuring multiphase fluid saturations for a baseline assessment of net CO2 storage capacity, potential rock-fluid interactions, and assessment in depleted gas reservoirs.
Extensive Monte Carlo response modelling has been performed to develop theoretical results for CO2 saturation. Characterization responses were generated from Monte Carlo N-Particle (MCNP) transport code simulating neutron particles and induced gamma-rays through a three-dimensional representation of materials. Simulations incorporated various conditions including the instrument, wellbore (fluids, tubing, casing, and cement), and the formation (lithology and mineralogy, porosity, and porosity-filled fluid compositions and densities).
Modelling is also used to estimate measurement sensitivities in explicit acquisition conditions, based on specific CCUS storage projects. In one scenario, pressure and density of CO2 is simulated at full saturation, at increasing pressure and density conditions. In another scenario, CO2 is simulated as a mixed fluid with CH4, and with water and residual oil also present. Quantitative gas saturation and differentiation of gas from oil, fresh, or saline water is available using pulsed neutron gamma ray ratio measurements.
The sensitivity of gas saturation measurements relative to the dynamic range of each fluid component, is a function of the composition, concentration, and density of the fluid. Induced gamma-ray count rates are highly affected by the presence of H that moderates neutron propagation. Relative to water and oil liquid phases, the presence of CO2 can be distinguished from H-bearing fluids (H2O, CH4) in capture and inelastic ratio gamma ray responses with greater accuracy.
A key objective is to evaluate the effectiveness of pulsed neutron formation characterization for baseline assessments, and for subsequent monitoring of injected CO2. Modelling results indicate high sensitivity for CO2 saturation analysis. This study provides a fundamental characterization required for accurate time-lapse saturation monitoring. A baseline multi-phase formation assessment is critical to evaluate suitability for monitoring CO2 injection. Post-injection assessment and long- term monitoring is necessary to determine equilibrium and changes in CO2 pressure and migration.
BIO: Geoff Page is the Europe Region Petrophysics Advisor for Baker Hughes, and also provides global support. He graduated in Physics at Imperial College and has now nearly 44 years with Baker Hughes, starting as a wireline engineer before also moving into LWD and Petrophysics in general, including 3 years subcontracted into a major oil company as an asset petrophysicist. He has been honoured with the SPWLA Distinguished technical achievement award, is an SPE technical editor, an Honorary teaching fellow at Aberdeen University, and has provided Petrophysics training to over 1500 people.
AFES is delighted to be involved in co-hosting Devex 2024. The call for abstracts is now out. For more information:
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A full pdf flyer can be downloaded here DEVEX 2024 – Abstracts Flyer_0.3