_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 224197, “Expanding Carbon Sequestration for Small-to-Medium Emitters: Pros and Cons of Coupling Simultaneous SCCO2/Brine Aquifer Injection or Water Alternating Gas With Saltwater Disposal Wells, ” by Stella I. Eyitayo, SPE, and Marshall C. Watson, SPE, Texas Tech University. The paper has not been peer-reviewed. _ As the urgency to combat climate change intensifies, developing innovative and efficient carbon-sequestration strategies to capture and store CO2 from industrial sources has become a critical priority. This paper reviews the simultaneous supercritical (SC) CO2-brine aquifer injection (SAI) and water-alternating-gas (WAG) methods for geologic carbon sequestration and proposes a novel integration with saltwater-disposal wells (SWDs). SAI-WAG Method The SAI-WAG strategy incorporates two scenarios: concurrent injection of CO2 and treated wastewater into a geological formation through a dual-structured well for disposal purposes, or alternating injection of treated water and CO2 by a single- or dual-string assembly. The latter scenario mirrors traditional WAG processes, which combine conventional waterflooding and CO2-injection methods into what is known as CO2-SWAG. Simultaneous injection also is called CO2-SWAG. Compared with CO2-WAG injection, CO2-SWAG injection provides better control over fluid mobility and enables more-stable gas displacement. Despite these advantages, SWAG injection presents challenges, including high costs for well completion, equipment, operations, and complex design. The SAI-WAG strategy offers significant economic advantages by eliminating the need to drill additional wells for geological carbon-storage activities. This approach leverages existing infrastructure for managing produced water (PW), which often involves injecting wastewater into aquifers for disposal. Such infrastructure is already well established in the US and Canada. The use of the SAI-WAG method for carbon storage is relatively new, and the literature exploring its advantages and disadvantages is limited. The primary challenges in enhanced recovery and carbon sequestration are associated with the high mobility of CO2. The SAI-WAG method addresses this challenge by improving trapping mechanisms, reducing freshwater demand, and managing large volumes of saline wastewater. This approach broadens the scope of carbon capture and storage (CCS), particularly for small and medium industrial emitters. Small-to-medium emitters are typically defined as industrial facilities or operations that emit between 10, 000 and 100, 000 metric tons of CO2 annually. These entities often face significant logistical and economic barriers to implementing large-scale CCS technologies. A comprehensive understanding of fluid dynamics, rock/fluid interactions, mineralization, and caprock-sealing efficiency is critical in effectively implementing and optimizing SAI-WAG methods. Table 2 of the complete paper compares SAI-WAG with other methods.
Chris Carpenter (Sun,) studied this question.