Comprehensive Review of Caprock-Sealing Mechanisms for Geologic Carbon Sequestration

Abstract

CO(2) capture and geologic sequestration is one of the most promising options for reducing atmospheric emissions of CO(2). Its viability and long-term safety, which depends on the caprock's sealing capacity and integrity, is crucial for implementing CO(2) geologic storage on a commercial scale. In terms of risk, CO(2) leakage mechanisms are classified as follows: diffusive loss of dissolved gas through the caprock, leakage through the pore spaces after breakthrough pressure has been exceeded, leakage through faults or fractures, and well leakage. An overview is presented in which the problems relating to CO(2) leakage are defined, dominant factors are considered, and the main results are given for these mechanisms, with the exception of well leakage. The overview includes the properties of the CO(2)-water/brine system, and the hydromechanics, geophysics, and geochemistry of the caprock-fluid system. In regard to leakage processes, leakage through faults or fracture networks can be rapid and catastrophic, whereas diffusive loss is usually low. The review identifies major research gaps and areas in need of additional study in regard to the mechanisms for geologic carbon sequestration and the effects of complicated processes on sealing capacity of caprock under reservoir conditions.

Diffusivity of Carbon Dioxide in Aqueous Solutions under Geologic Carbon Sequestration Conditions

“…For example, Lu et al used Raman spectroscopy to determine D of CO 2 in pure water in wide ranges of temperature (−5−200°C) and pressure (100−450 bar). 8 While the diffusivity of CO 2 in pure water has been studied extensively, under both ambient conditions and at high pressure and temperature, GCS conditions are characterized by high concentrations of brines as well as high concentrations of CO 2 , yet the effects of salinity and diffusing tracer concentration (CO 2 ) on D have not been studied thoroughly. Indeed, recent reports of the absolute value of the diffusion coefficient, D, in saline solutions and its dependence on salinity show significant variations.…”

Assessment of storage capacity for CO2in saline aquifers near hydrocarbon fields, northern Songliao Basin, China

“…Aft er injection, potential CO 2 leakage mechanisms are classifi ed as follows: diff usive loss of dissolved gas through the caprocks, leakage through the pore spaces if capillary entry pressure is exceeded, leakage through faults or fractures and well leakage. 7 If the impermeable seal is suitably thick and unbroken, then leakage through the caprock and faults or fractures will not occur. Extensive oil and gas exploration in hydrocarbon fi elds near HSFA has resulted in a high density of wells, which may present potential migration pathways and permit large-scale leakage.…”

Evaluating the Sealing Effectiveness of a Caprock-Fault System for CO2-EOR Storage: A Case Study of the Shengli Oilfield

“…In this project, a method of screening suitable target blocks for CO 2 -EOR storage was required and investigated. The effectiveness of a seal system is of overriding importance for realizing effective geological sequestration of CO 2 [16,17]; therefore, such systems must be evaluated carefully.…”