The Review of Deep Injection Wells

1. Abstract

Deep well injection is a waste disposal technology, also called subsurface injection or

underground injection. Through drilled wells, the wastes are injected into geologic strata that

have no potential to lead to migration of contaminants into current or future potable water

aquifers (FRTR 2010). Currently liquid waste, liquid radioactive waste, solids waste, even

CO2 waste are disposed by the application of deep injection wells technology around the

world. There are five classes of injection wells depending on the type of injected wastes and

the depth of the wells. Class I wells are most commonly used. Developing a deep injection

well system need an integrated effort of multidisciplinary that commands geological,

engineering, chemical, biological and legal expertises (Smith 1979, cited by Bigham 2003,

p27).

Although during the past 80 years, deep well injections have been ‘prepared, evaluated

ecologically, and judged positively’ (Tsang & Apps, 2005 p13), this technology is still

regarded as the temporary measures until the waste solidification technology is well

developed and popularly applied (Tsang & Apps, 2005).

2. Principle

Industrial effluents are hard to treat to an “acceptable level of purity” for surface

discharge (Bigham 2003). Deep injection wells provide a passage and storage for the wastes

and reduce lives and environment exposure to harmful organic and inorganic substances,

such as chemicals, heavy metals and harmful toxic, by eliminating them from the global

surface environment (EPA 2001, p16-17). This technology was started in 1930s by the USA

petroleum industry, commonly disposal of produced brine. Afterwards it has been gradually

used by many countries around the world.

There are some necessary components for the deep well structure, Figure 1. Firstly it is

must be deep enough to leave sufficient distance from existing and potential future drinking

water aquifers. Secondly there must be top and bottom impermeable confining zones to

enclose and isolate all the harmful contaminants within the injection zone. The injection

zone should be sufficiently porous and permeable to take in the contaminants (Bigham 2003).

And casing and grouting must be applied to isolate and prevent waste leakage into formations

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Figure 1 – A typical class I Injection Well, Western Australia 1998 (cited by Bigham, 2003)

other than the injection zones. And the disposal zone should be in a location with little

seismic activity, in order to minimize the risk of earthquake damage to the injection zone

formation and wells and the risk of triggering seismic events (Herbert 1996).

There are five classes of injection wells depending on the type of injected wastes and the

location of the wells, Table 1. Class I wells are most common and drilled for injecting

hazardous or non-hazardous fluids into isolated rock zones, around 1200 to 3000 meters

below the ground surface. Class I wells are stringently regulated under the Resource,

Conservation and Recovery Act to ensure that their use will prevent underground drinking

water sources from being contaminated (Tsang & Apps, 2005).

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Table 1- Injection well classification chart, GWPC 2007, p5

Class II wells are normally for the disposal of brine fluids that are the by-product

associated with oil and gas production. Class III wells are used for extracting valuable

minerals by injecting superheated steam or fluids and then extract them from the geologic

formation to collect valuable minerals (Nickolaus 2007). Class IV Injection Wells are used

for Hazardous and Radioactive Wastewater Disposal into or above underground sources of

drinking water (USDWs), but are currently forbidden in the USA due to threatening potential

of contamination of shallow drinking water sources (Nickolaus 2007). Class V wells are for

the wells those are not included in Classes I–IV. They may be shallow or deep, i.e. Drainage

wells, septic tanks, and cesspools ( Nickolaus 2007 and Pollution Issues, 2010).

The advantages of deep well injection are in a number of following aspects: isolating

wastes from biosphere, saving land for landfills and discharges (Bigham, 2003 p26), saving

cost for building structures to contain wastes, especially radioactive wastes and harmful

chemical wastes (Tsang & Apps, 2005 p13), avoiding transportation costs and meanwhile

eliminating the potential of leakage and spills in transportation etc (Tsang & Apps, 2005).

The limitations will be discussed in Chapter of Limitation of Deep Well Injection.

3. Applications

Up to nowadays liquid waste, liquid radioactive waste, solids waste, even CO2 waste are

disposed by the application of deep well injection technology around the world. In USA more

than half of the liquid hazardous waste and a large percentage of the non-hazardous industrial

liquid waste are discharged into more than 375,000 injection wells in all five categories

(Osborne 2001 p9), and Class I injection wells are only 484, up to 2007 (GWPC 2007).

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3.1 Liquid waste injection

Liquid wastes disposed in deep well injection mostly are brine, municipal sewage waste

and other liquid wastes such as from geothermal, food, chemical and nuclear power plants

and so on. From 1997 to 2003 in Germany, nearly 6.5 million m3 of brine were injected into

two horizons of 3 deep wells, which constructed in Kraak, Figure5. The cross section of the

well and geological formations are in Figure 6. The reservoir area is 26.5 km2; its effective

thickness varies 10 to 60 meters; porosity is 25% (Tsang & Apps, 2005 p408).

Figure 2 Aral overview-above ground facilities-Kraak storage site (Tsang & Apps, 2005 p406)

In California, USA, deep well injection technology has been used for more than half

century for the underground disposal of oil field brines. Only in 1994, around 75 million m3

of brine waters from oil fields were injected into deep wells (FAO 2010).

Figure 3 Cross section of brine disposal area (Tsang & Apps, 2005 p408)

In Taranaki, New Zealand, Origin Energy Resources NZ Ltd runs 7 deep wells to inject liquid wastes from oil and gas exploration and production activities. The discharge depth into

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a saline aquifer within the Matemateaonga Formation ranges from 1,126 and 1,176 m deep. The biggest total discharged volume for Waikapa-5 well is nearly 3 million m3, Table 2.

Table 2 - Summary of deep well injection in Taranaki, Taranaki Regional Council, 2009

3.2 Liquid radioactive waste injection

Traditional ground surface construction to store and isolate the radioactive waste could lead to leakage or other potential to discharge the radioactive waste into lakes or rivers to endanger biosphere. Deep well injection of liquid radioactive waste avoids this leakage hazards and also results in huge savings of cost and maintenance funds on building storage, anti-filtration measures and other protective constructions (Tsang & Apps, 2005 p13).

Table 2- Deep injection well sites for liquid waste in Russia (Tsang and Apps 2005, p14)

The application for injecting Liquid radioactive waste injection is mainly used in Russia and USA. The first Liquid radioactive waste injection well was started in 1963 in Russia.

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Two sand reservoir horizons were chosen as injection layers at depth of 270-320m and 314 – 386m. Up to 2005, totally 43.5 million m3 medium-level radioactive waste has been injected into this well. Some of other injection wells in Russia are listed in Table 2 as well (Tsang & Apps, 2005 p13).

Deep well injection is a temporary measure to deal with liquid radioactive waste until one day the technology to transfer the radioactive waste into harmless waste is effectively, efficiently and economically achieved, forecasted up to year 2115. In the past 80 years, injection projects of radioactive wastes have been ‘prepared, evaluated ecologically, and judged positively’ (Tsang & Apps, 2005 p13).

3.3 Injection of Solids

Solids injected into the deep wells generally are municipal sewage sludge, meat, bone-meals, residual ash and drilling waste (cuttings and mud). Basically the water and synthetic based muds and cuttings are discharged into the sites, but the oil-based muds have to be injected into the deep wells to prevent them from contaminating the environment (Tsang & Apps, 2005 p13).

Table 3 Locations of slurry injection jobs (Tsang & Apps, 2005 p408)

In Table 3, the majority of locations of slurry injection jobs are occurred in USA. The depth of wells ranges from round 1000 feet to 10000 feet, Table 4.

Table 4- Distribution for injection depth (Tsang & Apps, 2005 p408)

The most common operational problems were blocking (plugging) of the casing due to solids being settled out and excessive erosion of the casing and injection system components. Another problem is that the operational cost seems to be a main challenge to the expanded application of slurry injection (Tsang & Apps 2005 p539-547).

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Also deep well injection can be used for disposal of other solid waste. Croatia uses deep wells to discharge the biosolids of meat and residual ash. Figure 4 is the 2325 m deep well structure. The injection zone is located between 2042 to 2141 m. The risk for the Leg-1 well is assessed at 3.9 x 10-34 and Di-1 well is assessed at 2.4 x 10 -16 . All meet the standard of 1 x 10-10 (Brkic V, 2003).

Figure 4 – Well structure (Tsang and Apps 2005 p573)

3.4 CO2 injection

Nowadays, following the increasing attention to the emissions of greenhouse gas and global warming, more and more countries are focusing on how to reduce the CO2. Currently Germany has projected some deep wells to inject and sequestrate the CO2, basically in north-eastern Germany. The suitable horizons are ranging from 500 to 1500 meters deep. The injection reservoirs are mostly within the middle and upper Mesozoic strata, and their temperatures mainly vary from 40 to 60 0C, reservoir pressures mostly span 100 to 150 bar. So the injected CO2 generally are in supercritical state of liquid. The capacity for CO2

sequestration in analysed reservoirs is around from 50 million tonnes to 300 million tonnes (Tsang & Apps, 2005 p569-585).

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4. Cost Effective

Deep well injection can save plenty of cost in treating effluent to purity, building

structures to contain wastes, especially radioactive wastes and harmful chemical wastes,

avoiding transportation costs and meanwhile eliminating the potential of leakage and spills in

transportation etc (Tsang & Apps, 2005). Taking 3 Class I deep wells as example, which are

drilled in Northeast Area, USA, Table 5. The Depth is approximately 4,300 ft. The capital

cost only takes up 16% to 30% of the cost of other treatment methods, such as passive

evaporation and enhanced evaporation (Maliva 2006).

5. Limitation and regulations

There are some kinds of hazards associated with the deep injection wells, such as

contamination of groundwater and induction of seismic activities (Eelink 2010). Deep, high

pressure fluid injection induce earthquakes, which mostly are microearthquakes and only

measurable by seismometers in neighbouring wells. But a few of records are surface recorded

earthquakes. Since 1991 injection of high-pressure flow has caused over 4100 surface-

recorded earthquakes, the biggest one was a magnitude M4.3 (Tsang & Apps, 2005 p569-

585).

The threat to ground water was caught attention by a 1968- incident caused by the over

pressurization of the formation through the deep well injection in the Hammermill paper

company. This incident has caused groundwater contaminated in an area around five miles

from the injection well. However, such problems may be avoided when the deep injection wells

are properly ‘sited, constructed, and operated’. Then underground injection will be an effective

and environmentally safe method to dispose of wastes (Osborne 2001, p9).

The Federal government and many other countries have established laws, programs and

standards to reduce the relevant hazards and protect ground water sources (Osborne 2001 p9).

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Here taking the USA as the example to introduce how the underground well injection is

regulated by the authority.

Staring 1970, the USA Congress has established many relevant laws, policies, acts and

standards to control and monitor the development of deep injection wells for disposal of

hazardous waste, such as ‘the 1970 policy’; ‘the 1972 FWQA policy’, ‘Site-specific

Permitting’; “The No-migration Standard” etc. And the 10,000 Year Standard ruled that the

injectors shall show that “there would not be any migration of hazardous constituents outside

the injection zone for 10,000 years or until the wastes become non-hazardous.” (Herbert

1996). The current Underground Injection Control (UIC) program regulations require double

casing and cementing to avoid the two major ways of contamination of potable water

supplies, (Herbert 1996).

6. Conclusions

From 1930s into 21st century, deep well injection of wastes has played a significant role

in eliminating environmental contamination. On forecasting of the role of deep well injection,

any direct affects on biosphere are not expected. However deep well injection technology is

still regarded as the temporary measures until the waste solidification technology is

increasingly developed and further popularly applied.

Generally speaking, deep well Injection has been used safely across the world to dispose

of many types of wastes into ‘deep underground unused geologic formations where the waste

will permanently reside and attenuate over time’ (Bigham 2003, P1).

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