Energy Under Our Feet: Underground Storage
Energy demands naturally fluctuate throughout the year, with colder months typically being the most energy intensive. Natural gas is a key component of the world’s energy mix and is produced year-round to account for peak demand. During the summer, when supply exceeds demand, natural gas is routinely stored in vast underground formations where it can be easily extracted in the winter when demand outpaces production.
About 15% of all produced natural gas is injected back into the earth for storage at some point. Some above ground storage exists, but it pales in comparison to the quantities store in the subsurface. Constructing above ground storage vessels at the scale needed to rival natural underground storage is infeasible and uneconomical. Therefore, the vast majority of natural gas storage occurs in deep underground formations.
Depleted Reservoirs: A Natural Container
There are three types of underground formations commonly used to store natural gas: aquifers, salt caverns, and depleted reservoirs. Depleted reservoirs make up around 80% of all natural gas stored underground. Depleted reservoirs are formations that originally held natural gas before it was pumped out via an extraction well, making them perfect containers. Often existing extraction wells are repurposed to inject natural gas into the formation, saving the cost to drill another well and the associated environmental impact.
Aging Infrastructure: The Problem with Old Wells
While repurposing wells is a great practice, many repurposed wells are very old, having operated for years as an extraction well before being repurposed at the point they would typically be decommissioned. Age can present a number of issues in terms of well integrity. Over time cement and casing degrade, which can allow gases to freely migrate and potentially even cause a blowout. Further compounding the risk of well integrity failure is the fact that many of these older wells were not designed with modern safety measures (nested casing, pressure sensors, safety valves, or even cement). It’s estimated that more than 3,000 active underground storage wells in the U.S. are vulnerable to serious leaks due to obsolete well designs.
High Stakes: Loss of Well Integrity
Failures can be catastrophic for surrounding communities and the environment. In 2015 a San Aliso, California natural gas storage well suffered a blowout that released methane for 112 days until it was plugged, the largest single accidental release of greenhouse gases in US history. Some 5 billion cubic feet of methane and other pollutants spewed from the well, an amount equivalent to the annual greenhouse gas emissions of over 570,000 vehicles. This event forced thousands of residents to evacuate and doubled the methane emissions rate of the entire Los Angeles Basin. Investigation into the cause of the leak revealed the well predated redundant precautionary systems common in modern wells that prevent containment loss.
A similar incident occurred the same year in Champaign County, Illinois that resulted in the contamination of the Mahomet aquifer, the primary source of water for over 500,000 people in Eastern Illinois. The well to blame for the contamination experienced a blowout due to corroded casing and could have been prevented with proper monitoring.
Cement Degradation: A Looming Threat
Well integrity is a function of both well structure degradation (based on corrosion and exposure to heat/abrasion) and the safety standards and regulations in place during well construction (design, materials, and technologies).
Some of the oldest wells in the nation were drilled in PA, OH, NY, and WV. There are over 1,700 UGS wells in these states that were not originally designed for storage. The median age of these wells is 84 years, with 210 of the wells being over 100 years old. Each of these wells have the potential to be an environmental disaster if appropriate steps are not taken to ensure their integrity.
Monitoring & Intervention: Avoiding Disaster
To ensure reliable energy and mitigate environmental disaster, consistent monitoring and timely intervention are critical. Sealing UGS wells can prevent methane contamination of aquifers and the atmosphere in addition to preventing the loss of valuable natural gas that took considerable effort to extract.
Consistent monitoring requires commitment and discipline from gas storage companies, but intervention options can be inconsistent and costly. BioSqueeze® is a new well intervention technology that harnesses natural biomineralization to permanently seals leaks in degraded cement and casing. BioSqueeze® has proven to be much more effective than traditional remediation technologies, having sealed over 40 leaks across 6 states and saving companies hundreds of thousands of dollars.
