Field-Scale Simulations of Water-Alternating-Gas Injection in Morrowan Fluvial Sandstones of Stewart Field, Kansas, Using Captured CO2 from an Ethanol Plant
Authors: Longe PO , Molomjav Sanjaajav , Barati R. , Tsau Jyun-Syung , Musgrove Spencer , Villalobos Jeff , D'Erasmo Jaques , Alhajeri Mubarak M. 
Published: February 2024

The technique of CO2-water alternating gas (WAG) for enhanced oil recovery (EOR) and carbon storage has become a viable alternative method to reduce the atmospheric concentration of CO2, when compared with other utilization methods. However, CO2-EOR (utilization) and carbon sequestration processes involve modeling strongly complex mechanisms in subsurface formations using advanced numerical simulation methods. In Kansas, a CCUS opportunity is ongoing which involves capturing CO2 directly from a nearby ethanol plant for CO2–EOR. This paper aims to assess the performance of the CO2–WAG project in a mature, depleted reservoir in the Stewart Field Unit (SFU), Finney County, Kansas. A few fields and laboratory EOR studies have been published on deeper parts of the Morrow formation in OK and TX, however, the shallow incised valley fluvial morrow sands in the SFU presents a different perspective in terms of depth, rock-fluid properties and pressure of its complex subsurface system.

This study presents a field-scale heterogenous compositional reservoir flow model that is prepared using a static geo-model that was further modified based on the outcomes of the waterflooding phase. Due to the water-sensitive nature of the Morrow sands coupled with organic and inorganic scales that caused near-wellbore damage, field development incorporated hydraulic fractures that have apparently gone through compaction/dilation during the injection production phases. These processes were simulated in the model coupled with CO2 dissolution to simulate the underlying physical-chemical mechanisms. Furthermore, an equation of state, tuned with laboratory fluid and minimum miscible pressure (MMP) data, was used to predict the thermodynamic fluid properties. The primary, secondary and current CO2–tertiary recovery phases of the model were historically matched with 55 years of historical data. The successful history matching was properly achieved by modification of relative permeability curves, directional permeability, and near-wellbore damage.

The primary, secondary, and tertiary cumulative recovery factors of 11.5%, 29%, and 32% were reported, respectively. The possible explanations to the low recovery during the CO2–EOR phases are formation damage due to water sensitivity, organic scale and wellbore integrity issues. Based on the final history-match, we investigated the influence of several recommended CO2-WAG scenarios and re-opening of existing wells. The CO2-WAGs scenarios proposed were adapted to focus on the east side or west side of the field due to limited CO2 availability and CO2 transport logistics. Forecast results showed an incremental oil recovery factor of between 1 – 3% for the WAG cases designed for the west and east sections. To achieve a higher percentage of incremental oil recovery and sequestration of CO2 within the morrow fluvial sand, field implementation of optimized WAG scenarios with remedial well treatments is recommended. Conclusively, this study can provide a good framework for optimizing potential CO2–WAG projects in the other geologically similar fluvial morrow formations.