Participation in over 80 carbon capture and sequestration (CCS) projects spanning 25 years has led to the evolution of a recommended well-based appraisal workflow for CO2 sequestration in saline aquifers. Interpretation methods are expressly adapted for CCS applications to resolve key reservoir parameters, constrain field-scale modeling, provide answers required for the permitting process, and derisk unique CCS evaluation challenges, such as
• Storage capacity
• Injectivity
• Containment
A challenge complicating all of the above is the eventual impact of three-way interaction among rock matrix, brine, and (impure) CO2 streams.
Most logging, sampling, and laboratory techniques are adapted from established domains such as enhanced oil recovery, underground gas storage, and unconventional reservoir evaluation, though some CCS-specific innovation is also needed. Storage evaluation begins with established methods for lithology, porosity, permeability, and pressure, while special core analysis (SCAL) determines CO2 storage efficiency and relative permeability. Containment evaluation spans multiple disciplines and methods: the petrophysicist's task to quantify seal capacity relies heavily on laboratory analysis while geologists leverage downhole imaging tools to verify caprock structural/tectonic integrity. Geomechanics engineers define safe injection pressure via mechanical earth models (MEMs) built on advanced acoustic logs calibrated by core geomechanics, wellbore failure observations, and in-situ stress tests. The impact of rock-brine-CO2 interactions are studied via custom SCAL experiments and/or pore-scale digital rock simulations that faithfully represent chemical and thermal processes. Wireline formation tester samples provide representative formation brine as feedstock for SCAL. Water samples also enable operators to prove injection within regulatory limits, while establishing baselines for the future monitoring program. Examples applied to recent CCS projects in North America are presented. All of the above data need to be integrated in a CCS model predicting the CO2 plume behavior across the area of interest and within multiple horizons.
If global CO2 emissions continue at current rates, global warming threatens to exceed 1.5 deg C within the 2030's. National policies and international emissions reduction agreements address this urgent threat by financially accelerating scientific ingenuity and economic viability for limiting carbon emissions from industrial processes prior to release into the atmosphere. One pathway by which CO2 emitters can reduce carbon emissions is by capturing and storing it in deep underground geologic formations. New initiatives have incentivized projects, increased understanding of storage safety, efficacy, and economics, and demonstrated the growing potential for CCS in the coming years. In the United States, the Inflation Reduction Act alone directs nearly USD 400 billion in federal funding into clean energy solutions.
