Carbon Geologic Sequestration
Carbon Capture, Utilization, and Storage (CCUS) is a climate change mitigation technology involving removal of carbon dioxide (CO2) from flue gas and reusing the same for production of industrial byproducts or permanently storing the gas deep in the earth. Geologic formations in which CO2 is stored include oil and gas reservoirs, coalbed seams and deep saline reservoirs - structures that have stored carbon dioxide along with crude oil, natural gas, and brine for millions of years. The captured CO2 can also be used to recover trapped oil and gas in depleted reservoirs, a process referred to as Enhanced Oil Recovery (EOR).
Since 2011, TBirdie Consulting has been providing consulting services on a multi-million dollar Department of Energy (DOE) sponsored pilot scale project to demonstrate the feasibility of CCUS technology. Based on this experience, the company offers a full range of service to support implementation of the technology from conception to closure, a period spanning several decades.
Site selection is a key part of a CCUS project and we have the experience to carefully review and analyze the data to screen sites with maximum storage potential and minimal seismic risk. We also conduct market research to determine commercial value of the captured CO2 in your geographic area. Our services include recommendation for most economical and effective carbon capture and compression technologies. Cost estimates are provided for site characterization, permitting, carbon capture/compression, transportation, injection, monitoring, reporting, and site closure. The amount of carbon credits available in the international market to offset the cost of CCUS is also researched and summarized in our feasibility study.
Geologic sequestration of carbon dioxide in the United States is regulated by the Environmental Protection Agency (EPA) via the Class VI injection permit. As part of the permitting process, a detailed characterization of the injection and confining zones is required in order to ensure that the injected CO2 will remain permanently sequestered in the subsurface. For typical hydrocarbon extraction, derivation of the bulk petrophysical properties is adequate to predict hydrocarbon recovery rates. However, for sequestration purposes, it is necessary to conduct detailed petrophysical analysis and characterization due to the buoyant nature of CO2, and to account for sequestration in each of the four primary trapping mechanisms in the subsurface: structural, residual, solubility, and mineralogical. We specialize in the application of advanced characterization techniques which have been approved by EPA for Class VI permitting. The data sets that we acquire at a sequestration site include:
- Modern suite of geophysical logs for determining the petrophysical properties of the formations
- Injection tests to generate aquifer response data sets for model based characterization and to derive the fracture gradient
- 3-D seismic surveys for geologic structure and impedance mapping on a regional scale
- Drill Stem Tests to obtain in-situ pressure information and for estimating rock permeability
- Swab samples for geochemical analysis and CO2 kinetics
- Core samples for obtaining laboratory based estimates of porosity and permeability, mineralogical characterization, and establishing CO2 compatibility
The outcome of the site characterization process is the development of data sets necessary for developing a multiphase flow and transport model which predicts the spatial extent of the CO2 plume and pressure field. The model projections are also used to identify optimal locations for the injection and monitoring wells.
The three main types of carbon capture technologies include:
- Oxyfuel combustion
Pre-combustion involves capturing CO2 prior to combustion and is utilized at gasification-based plants where fuel is first converted into gas if necessary by applying heat under pressure in the presence of steam and oxygen. In post-combustion, CO2 is removed from the flue gas after combustion and is mainly applicable to conventional coal, oil, or gas fired power plants. In an oxy-combustion process, an oxygen source is used instead of air for combustion, yielding a stream that is mostly CO2 and without nitrogen. The resulting flue gas is mainly (low volume) CO2 which facilitates removal of pollutants such as mercury and sulfur oxides. This process has the potential to become the capture method of choice for new natural gas fired power plants, as there will be minimal expense for carbon capture.
Both pre and post combustion methods rely on the following four technologies for capture:
- Solvent-based CO2 capture involves using a liquid medium for chemical-reaction or physical absorption of CO2.
- Sorbent-based processes involve adsorption of selected components of the gas at the surface and pores of a microporous solid.
- Membrane-based CO2 capture uses permeable materials that allows for the selective transport and separation of CO2 from flue gas for post-combustion capture, and syngas in pre-combustion systems.
- Novel Concepts are under investigation and include hybrid systems which combine attributes from multiple technologies, novel processes, and nanomaterials.
The DOE is also actively supporting research to maximize the potential of oxy-fuel combustion by focusing on combining oxy and chemical looping combustion, and incorporating supercritical CO2 power cycles and pressure gain combustion.
TBirdie Consulting is actively following developments in the carbon capture field and have the necessary skillsets and industry relationships with combustion cycle experts for identifying the most efficient technology for our client's needs.
An EPA Class VI permit is required for CO2 sequestration in all states except North Dakota. The primary goal of EPA is to ensure containment of the injected CO2 within the injection zone in order to prevent contamination of drinking water aquifers. The permit consist of several formal plans related to injection well construction, stimulation, operations, reservoir characterization, multiphase modeling, testing and monitoring, reporting, post-injection site care and closure, and demonstrating financial responsibility. TBirdie Consulting has over six years of experience dealing with the EPA regulators at the regional and national level in support of Class VI permitting.
On approval of the injection permit, we develop the physical and electronic infrastructure necessary for injection, and install the equipment necessary for monitoring the plume and pressure fields, and ensuring safe operating conditions. We can also provide the staff necessary to oversee operations and respond to emergency conditions requiring remedial measures as outlined in the injection permit.
Monitoring Verification and Accounting
To ensure that the injected CO2 remains confined in the injection zone, EPA requires the implementation of a broad set of monitoring technologies to track the plume and pressure front. Broadly speaking, the monitoring technologies are divided into two categories: Direct and Indirect monitoring. Direct monitoring refers to actual measurements of the system state such as pressure, temperature, and geochemical composition. Indirect monitoring refers to a set of auxiliary data from which the location of the plume and the pressure front can be deduced. Examples of indirect method of pressure monitoring include satellite based Interferometric Synthetic Aperture Radar (InSAR), which measures land deformation from which the pressure distribution in the injection zone can be estimated in addition to detecting leakage in caprock. An example of an indirect plume monitoring technology would be Croswell Seismic Profile.
For each project, we develop a site-specific monitoring plan to assist in tracking the plume and pressures, manage operations, control risks, and comply with regulations. Continuous monitoring is critical for management of operations/risks and to update the multiphase predictive model. Deviations from model projections require implementation of remedial measures specified in the permit. The following is a list of monitoring technologies that we can implement, and which have been approved by EPA for Class VI projects:
- Optical CO2 sensors
- Atmospheric tracers
- Eddy covariance flux measurements
- Geochemical analysis of shallow water
- Surface displacement using optical technologies
- 3-D seismic survey
- Vertical seismic profiling
- Soil-gas geochemistry and CO2 flux
- Fiber optic array with seismic source in injection well
Wells in Injection and Confining Zones
- Continuous Active Source Seismic
- Croswell seismic profile
- Chemical tracer
- U-Tube (for in-situ geochemical analysis of multiphase fluids)
- Quartz pressure/temperature gage
Regulatory Reporting and Validation
The Class VI rule requires quarterly reporting of the monitored data and demonstration via computer modeling that the CO2 plume and pressure front are evolving as projected in the permit application. Any deviation necessitates an update of the predicted path of the plume and pressure field, along with modification to the monitoring plans. All monitoring, validating, and reporting requirements are fulfilled by our staff in support of the permit requirements.
Post Injection Site Care (PISC) and Site Closure
As per Class VI rule, the default (plume/pressure) monitoring period after cessation of CO2 injection is 50 years. Periodic reporting is to continue during this period until stabilization of the plume/pressure and non-endangerment can be demonstrated. We have all the procedures and experience necessary to accomplish the Class VI non-endangerment demonstration in the shortest possible time. Based on detailed analysis and computer based projections, we have previously petitioned the EPA and successfully reduced the PISC period to as little as four years.
Our knowledge of international carbon markets and connections with carbon traders involved in purchasing credits from verifiable carbon sequestration operations can help offset the cost of CCUS for our clients. We are also familiar with provisions of the recently passed 45Q legislation in the U.S. congress, which creates credits for carbon storage and utilization to increase oil production.
The DOE's Carbon Use and Reuse Technology initiative involves development of technologies for creating a commodity market for CO2. Present research is focused on producing the following byproduct with CO2:
TBirdie Consulting is actively monitoring the developments in this area so that our clients can reap additional financial benefits from CO2 capture as these technologies mature and are ready for commercial use.
Enhanced Oil Recovery
The cost of carbon capture can be mitigated by selling CO2 to support enhanced oil recovery (EOR) operations in depleted oil fields. Injecting (miscible) CO2 in mature fields reduces the surface tension and viscosity of the trapped oil, thereby facilitating its release. CO2 that is produced in gaseous phase along with oil is re-injected in a feedback loop. Some of the CO2 remains trapped as storage and contributes to the sequestration goal.