CO2 Sequestration in a Limited-Data Depleted Gas Reservoir for Reservoir Capacity Assessment and Injection Optimization - Case Study
Authors: Kaldas Michael Nashaat , Saunders Bryan , Nasiri Amir , Barben Stacia 
Published: January 2023

Greenhouse gases are a big risk to our life on the planet, as they absorb the infrared radiation which results in trapping the heat in the atmosphere and making our planet warmer. Carbon dioxide (CO2) is one of the key and major greenhouse gases that are emitted by humans. Some of these gases occur naturally in the atmosphere, but human activities have changed their concentrations. As per the U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020 "From the pre-industrial era (i.e., ending about 1750) to 2020, concentrations of these greenhouse gases have increased globally by 47.9, 168.4, and 23.3 percent, respectively (IPCC 2013; NOAA/ESRL 2022a, 2022b, 2022c)".

There are different sources of CO2 emissions as will be mentioned later. Carbon capture and sequestration (CCS) technologies are considered a practical option to protect the atmosphere from these emissions. This is done through capturing the CO2 from its sources, transporting it to the injection location and then sequestrate it into deep formations. This CO2 could be injected in saline aquifers or depleted oil and gas reservoirs for storing purposes or it could be injected in producing oil and gas reservoirs for enhanced oil and gas recovery respectively. From the subsurface perspective, there are three key parameters that needs to be considered in the selection of any reservoir:

Storage Capacity Storage Containment CO2 Injectivity

This paper is a case study of CO2 sequestration in a depleted gas condensate reservoir that was produced down to abandonment pressure. The objective of the project was to deliver a detailed site characterization and reservoir simulation for a Carbon Sequestration program for Castex Energy in Louisiana. Castex Energy is pursuing the development of a CO2 injection hub to support permanent geological sequestration with CO2 supplied from third party sources in the southern Louisiana area. The CCS project will utilize acreage from a depleted gas reservoir in state waters in southern Louisiana.

The ultimate objective of this phase of the project is to create a geological model and conduct preliminary reservoir simulations that will be required for Class VI permit to construct the applications. This has been implemented through the following key tasks:

Building the static model and generate several realizations for the static properties (Facies, Porosity and Permeability): this was a key step to come up with many realizations to capture the static model data uncertainty. Implementing P/Z analysis to have a good understanding about the initial gas in place History matching though tuning the model by combining the static and dynamic uncertain parameters Evaluating the reservoir storage capacity and optimizing the CO2 injection performance and plume movement

The model was a very powerful tool to quantify the reservoir storage capacity and to have a good understanding about the CO2 injectivity and plume movement in the reservoir. One of the key recommendations of the study was to implement a detailed analysis on the structure model, as the ultimate plume location is sensitive to the structural interpretation.