Constructing a reliably permanent buffer between a water table, the earth, and the wellbore using cement is immensely difficult. Steel casings can leak at the connections or corrode from acids. Cement can deteriorate over time, but leaks also happen when cement shrinks, develops cracks or channels, or is lost into the surrounding rock when it's applied. When this occurs, gases and liquids leak out of the casing or, just as importantly, move into, up, and out of the well through faulty cement between the casing and the rock wall.
Loss of Well Integrity
The loss of well integrity can lead to fracking chemicals (and naturally occurring contaminants) migrating into higher aquifers and impacting groundwater, particularly with the very high pressure injections needed to frack shale and tight gas wells. Repeated fracking can also cause well casing failures, creating opportunities for contamination.
Faulty Well Casing
Faulty well casing and cementing is the cause of most well integrity failures. Though the risk of failure in the short-term may be low, the steel and cement casing in the wellbore are subject to greater risk of mechanical or chemical failure over time. Data from the Marcellus Shale 'play' published in the Journal of Marine and Petroleum Geology found six - seven percent of new shale gas wells were faulty and leaking gas. Six percent may not seem very high a failure rate, but for the 40,000 gas wells planned for Queensland it would mean around 2,400 leaking wells.
After 20 years this failure rate could increase to 60%, as wells corrode and cement casings degrade. A well-known expert in this field, Dr Anthony Ingraffea, says that all wells will fail in time. Even industry studies have reported that over a 30 year period anywhere between 2 and 60 percent of oil and gas wells fail, depending on the expertise of the company and the wells' location and age. The issue here is, to be safe into perpetuity, these wells need be constructed to last forever.
The industry's inability to guarantee the integrity of the wells it drills is not the only problem. Even if shale gas well casings could be guaranteed for millenia, it would still not solve the problems of:
- The significant issue of air pollution and greenhouse gas emissions, a product of the process even when wells perform as intended
- The behaviour of tonnes of toxic chemicals pumped deep underground, and their safety into the future our children and grandchildren will inhabit
- The issue of the increased opportunity that fracking provides for chemical spills and industrial accidents
- The lack of an effective treatment or method of safely disposing of toxic flowback from completed frack jobs
In the past, the low recovery rates for shale oil and gas, combined with the steep decline in gas production (which can fall by as much as 60 to 80 percent after the first year or so), meant infill drilling had to be undertaken to maintain gas production. Infill drilling is the process of drilling increasing numbers of closely spaced wells as the gas depletes.
Today, however, investment in new extraction technology has enabled unconventional oil and gas miners to use 'microseismic' and 'refracks' to improve the productivity and profitability of old wells.
According to Halliburton, by re-perforating the original interval and pumping a volume at least 25 percent larger than the previous frack, recovery rates can be improved by up to 8 - 10 percent. Because it's estimated that only about 10 percent of the GIP (gas in place) is recovered with the initial 'completion', refracking technology is extremely worthwhile for unconventional gas companies. It increases gas production from existing wells without the high cost of having to drill new wells. Refracking is an especially effective technique on tight deposits.
Schlumberger, the mega-giant in the oil and gas services sector, markets some of the customised refracking technology. CEO Paal Kibsgaard believes the revenue opportunities from refracking are worth billions. Because refracking offers such a rich windfall and the company is so confident of its ability to identify the right candidate wells, Schlumberger is:
prepared to take significant risks, in terms of how we go about doing this refracturing work.
To make refracking an even more attractive proposition to oil and gas drillers, Schlumberger offers refracking clients a risk-free no win, no fee deal. The client gas companies don't pay Schlumberger unless their gas production increases beyond an agreed level.
So, refracking substantially reduces drilling costs, increases gas production and can be done on risk-free terms for companies with gas wells that are 'the right candidates'. Setting aside the fact that refracking is not without its own set of technical risks and challenges, the health and well being of communities who live on top of subterranean shale and tight gas deposits should be an important consideration too.
Each refrack uses 25 percent more water, mixed with more toxic additives, than the last. Each refrack generates a new load of highly contaminated wastewater. Each refrack restresses the well casings with 6000 to 8000 PSI of pressure. Each refrack increases the danger of surface contamination through accidental spills or leaks of concentrated chemicals.