Deep Injection Underground Disposal

CBM Operators can inject produced water into deeper underground reservoirs that are not classified as USDWs. Most United States territories contain these reservoirs. The reservoirs’ ability to accept large volumes of injected water and their depths are highly variable. Deep injection requires a permit from the state regulatory agency and could require a permit from the US EPA if Indian Tribal Land is involved.

Deep injection can be very limited by economics if suitable injection zones are too deep or cannot accept sufficient fluid relative to the volume of water produced by CBM development. Deep injection has the advantage of protecting surface water resources but unfortunately the CBM water resource is permanently lost. In addition, deep injection wells are dedicated facilities that can be extremely expensive to drill and operate, and often do not accept the same quantity of water over time.

Deep Well injection systems most often operate under high pressure, and if the system fails for any reason the entire CBM well field will be shut down until an alternative method of water handling can be found. Deep-well injection can cost up to $4/bbl in some parts of the west region due to limited transport and handling infrastructure and each deep well can cost $400,000 to $3 million to drill. There are additional costs of pumping and piping all of the water to the central deep injection well.

Comparison of Injection Methods

In addition to the various methods of surface discharge that dispose of CBM produced water; each of the four methods of water “injection” listed below has its own impact on operating costs and water conservation:

1. Central point deep injection:

a. Impact

i. "disposal" of water, not accessible for future use
ii. eliminates natural tributary water flow
iii. negatively impacts water rights
iv. requires extensive surface disturbance

b. How it works:

i. water from many CBM wells piped to one location
ii. very high pressure and large volumes of water
iii. usable water is often mixed with the bad water at extreme depths
iv. requires large capacity receiving zone (permeability and porosity)
v. expensive to drill and operate
vi. HIGH risk of over pressurizing zone, and well failure

2. Central point shallow injection:

a. Impact:

i. "retention" of water, moved from original geographic location ii. may change natural tributary water flow iii. may have negative impact on water rights iv. requires extensive surface disturbance

b. How it works:

i. water from many CBM wells piped to one location
ii. high pressure and large volumes of water
iii. good water is usually mixed with water of same quality
iv. requires large capacity receiving zone (permeability and porosity)
v. higher risk of vertical movement of water back to coal seam or surface vi. moderate cost to drill and operate
vii. HIGH risk of over pressurizing zone, and well failure

3. Central point injection into dewatered coal seam:

a. Impact:

i. "retention" or "disposal" of water, moved from original geographic location
ii. may change natural tributary water flow
iii. may have negative impact on water rights
iv. may negatively impact surrounding gas production
v. requires extensive surface disturbance

b. How it works:

i. water from many CBM wells piped to non producing CBM well
ii. high pressure and large volumes of water
iii. good water is usually mixed with water of same quality
iv. requires large capacity receiving zone (permeability and porosity)
v. risk of impact to adjacent producing CBM wells
vi. low to moderate cost to drill and operate
vii. HIGH risk of over pressurizing zone and well failure

4. In-Bore Aquifer Recharge Injection (ARID):

a. Impact:

i. "retention" of water in current geographic location
ii. generally no impact to natural tributary water flow
iii. usually has beneficial impact on water rights
iv. easy access for future use by landowner
v. requires no surface disturbance

b. How it works:

i. produced water never comes to the surface
ii. produced water pumped to a shallow receiving zone all in the same well bore
iii. low pressure and low volume of water
iv. good water is mixed with water of similar quality
v. can use lower capacity receiving zone (permeability and porosity)
vi. limited risk of impact to producing CBM wells
vii. no extra drilling and inexpensive to implement and operate
viii. Low risk of over pressurizing zone, thus higher success rate

Why In-bore Aquifer Recharge Injection:

While it should be noted that shallow injection with in-bore aquifer recharge is not always an option, when the geology and water quality permits, it is the best option for cost savings, reduced environmental impact, and water conservation. We will guarantee the results when we recommend an In-bore Aquifer Recharge Injection System for implementation.

We estimate that In-bore Aquifer Recharge Injection will save Operators about $250k for wells that produce water on the average 15gpm over a five year period verses other discharge or injection systems. During that same five year period Operators will have conserved about 39.5 MILLION gallons of water per well that the landowner can access for future use as needed. Just consider how much cost and water can be saved on 100 wells, 1000 wells? With the corporate pressures to become more profitable, and with community concerns over water shortages, there is a desire to eliminate the expensive disposal of good usable CBM produced water.