A number of technologies developed by the gas storage industry in the United States and Europe have potential application to CO2 sequestration. The most utilized method of storing natural gas in geologic formations is injection into
Develop better understanding of maximum delta temperature that casings can withstand without failure of cement or joints.
Improve corrosion management methods to enhance availability (especially bacterial control).
Develop new tools (e. g., logging) and techniques to verify integrity of casing strings.
Research improvements in deliverability by mechanical means such as new coil tubing tools.
Find new approach to handling produced water.
Develop cost-effective means to remove water at end of withdrawal season. Develop ways to delay or prevent "watering off.” Prevent water from encroaching on wellbore and reducing relative permeability.
Lost gas: condensates, migration, fractured reservoirs.
Develop technology to improve ability to interconnect formations via field experiments to demonstrate deliverability and interpret fuzzy logic.
New approaches to modeling gas cycling to and from storage.
Inventory verification: better techniques to handle changing uses of reservoir fields, e. g., average pressure.
Optimize software that ties industry well data, hydraulics (pipe line simulation) characterization and system dispatch.
Correct wellbore damage.
Determine near wellbore hydraulics.
depleted oil or gas reservoirs because these reservoirs have effective seals that prevented the escape of hydrocarbons for thousands of years. Thus the risks of losing stored natural gas are minimal (Benson et al., 2002).
However, depleted hydrocarbon fields in areas where natural gas storage fields are required are insufficient. The same is also is true for CO2 sequestration where sites are needed in the industrial and highly populated areas, where depleted oil and gas fields are rare or nonexistent. The gas industry has overcome this obstacle in part by creating storage fields in aquifers, and this technique is an obvious choice for sequestration of carbon dioxide in many industrial and highly populated regions around the world.
Storage of natural gas in aquifers is the process of injecting gas into an aquifer of high or reasonably high permeability under structural conditions that mimic natural oil and gas reservoirs, for example, anticline highs or up – dip pinch-outs. In addition, a target aquifer must be free of faults so that the stored gas will not escape through fault planes.
The keys to the success of storing natural gas and/or carbon dioxide in geologic formations are site selection and accurate delineation of the host formation to ensure that the formations are continuous and extend over a wide area without faults or other discontinuities that would allow escape of the injected gas. A storage zone must be contained below impermeable overlying beds, preferably structurally undisturbed, and laterally continuous to store large quantities of gas to be injected continuously over a very long period. In addition, for any method of gas storage or carbon sequestration to have value, a reliable monitoring procedure must ensure that the process follows the projected path. Monitoring must also implement early remedial action when required.
A number of technologies developed by the gas storage industry in the United States and Europe have potential application to CO2 sequestration. Table 8.3 identifies those technologies.
Successful CO2 sequestration requires participation by many disciplines. The technology developed by the underground gas storage industry will have significant application to CO2 sequestration. Gas storage operators have developed a technology portfolio that is not widely known or generally available across the E&P industry. The availability of this technology and increasing the awareness of these possibilities could prevent duplication of effort, resulting in considerable savings and providing more effective CO2 sequestration (see Figure 8.8).
The gas storage industry has successfully operated storage fields for over 90 years and has developed a number of procedures and technologies that can directly assist with the sequestration of CO2. Many of the technologies utilized by gas storage operators were developed by and adopted from the oil and gas industries.
Several technologies and procedures have been developed by the gas storage industry directly to meet customer needs. This is especially true in the area of aquifer gas storage which includes a portfolio of technologies unique to the aquifer storage business. All the existing gas storage technology can
Development Costs Type per Bcf of Working Gas Capacity
$5 – $6 million
6-to-12 Cycle Salt Cavern
$10 – $12 million As much as $25 million
Northeast and West
Costs of development of working gas storage per billion cubic feet of working gas capacity. (From Federal Energy Regulatory Commission Report Docket AD04-11-000.)
provide significant insights for the CO2 sequestration industry. The aquifer gas storage area may have the greatest contribution to make to the CO2 sequestration business (see Table 8.3). Gas storage operators have accumulated a significant knowledge base for the safe and effective storage of natural gas. While unwanted gas migration has occurred because of mechanical problems with wells and geologic factors, gas storage overall has been effectively and efficiently performed.
 The wind profile data is from work done in 2008 as part of the Western Wind Integration Study, an ongoing project of the NREL (http://wind. nrel. gov/Web_nrel/). The PSCO load profile represents its average daily loads for 2007 and 2008 based on its Federal Energy Regulatory Commission (FERC) Form 714.
 Bentek and the Independent Petroleum Association of the Mountain States (IPAMS) repeatedly tried to obtain 2008 hourly wind generation data from PSCO. All requests were denied because PSCO contends that the data represent confidential trading information.
+ PSCO uses the Cougar model to measure the cost impacts of integration.
 The Cherokee 4 boiler is a 352-MW unit in a 717-MW coal-fired plant in Denver County, CO.
 While most plant components are designed to handle cycling, generation changes directly impact water systems, pulverizers, boilers, scrubbers, heat exchangers, and generators. Catastrophic failures resulting from excessive cycling arise commonly from fatigue, corrosion, and cycling-related creep. Such failures may eventually cause plant shutdowns and large capital expenditures for replacement of damaged equipment.
 PHES facilities should have a fail-safe overpumping safety design.
• This design should be independent of water level control systems, as water level and monitoring control and overpumping protection are separate systems.
 Power electronics motor drive to energize motor pump during the pumping cycle
• Generator exciter and rectifier to extract electricity from the turbine generator during the generating cycle
• Grid tie inverter to condition the power to 60 Hz, 480 Vac; includes rectifier function in the case of a local wind turbine power source
• A 480 Vac circuit breaker panel for protective functions and power routing
• A transformer to convert 480 Vac to 220 Vac and 120 Vac for user load power
 Although aquifer bubbles are not rigid bodies, the time scale at which the air-water interfaces migrate is much longer than CAES storage cycles and therefore porous rock systems can be approximated as fixed-volume air reservoirs in this context.
 The range of efficiencies for a system without a recuperator reflects changes in system performance due to varying storage pressures (pS = 20 to 70 bar). The change in efficiency was <1% for a system with a recuperator.
 Electrodes require high electric conductivity and good wettability.
• Charging voltage must be limited to a maximum of 1.7 V to avoid damage to the carbon current collectors.
• Good electrical contact to the bipolar plates and current collectors is essential and best achieved when the activation layers are thermally bonded to the current collector.
• Access of oxygen to the negative electrolyte compartment must be avoided.
 Storage of energy in separate tanks away from the cell stack
• Capability of increasing energy capacity simply by adding more solution
• Ability of electrolyte solution to act as a coolant when pumped through the stacks
• Lack of contamination from cross mixing of electrolytes
• Low cost based on indefinite lifetimes of solutions
Practical applications of solar thermal energy storage include, but are not limited to
• Space heating and cooling
• Domestic water heating
• Industrial and agricultural process heating
• Solar cooking
• Small power plants and water pumps
 Dish engine generators (buffer storage)
• Large concentrating solar power plants (typically 3 to 12 hours of storage)