**3. Characterization**

What do all of these applications have in common, and how do they differ? To differentiate, we'll look at some of the physical aspects of fracturing:

**Injectate Volume** – How much fluid is injected? Note that we could also consider injection flow rate here although the total volume injected is clearly related to flow rate.

**Nature of the Injectate:** Is it just water or does it include chemical additives?

**Proppant:** Is proppant being injected to hold the fracture open after treatment?

**Fracture Propagation:** Are we creating a fracture simply to determine the strength of the rock and stopping, or after initiation, are we going to try to propagate that fracture further?

**Pressure:** What pressures are applied?

The range of suitable "geologic reservoirs" includes coal basins, depleted oil and gas reservoirs and saline aquifers. Although this technology is still under development with many studies being conducted worldwide there is, as yet, no large scale development. It is anticipated, depending on the storage target and it is noted that the targets mentioned above are high permeability reservoirs, that hydraulic fracturing may play a role in this industry. Again, we have assumed that hydraulic fracturing in this role will be similar in scale to that employed in

Hydraulic fracturing in CBM wells is performed in similar fashion and for similar purposes as for conventional oil and gas wells [9]. The major difference is that of scale in that the CBM reservoirs, normally being nearer to surface, require lower pressures, less volume and fewer

Fracture pressures are up to 5,000 psi and total injected volume per fracture ranging up to

The objective of CMM drainage is to reduce the methane content of coal seams prior to mining both for safety and environmental reasons and also as an additional revenue stream. Hydraulic fracturing both with and without sand proppant is used to enhance the production of methane from the coal. These treatments are conducted from both vertical holes and horizontal, in-seam drill holes. The scale of treatments varies widely but are typically smaller than CBM stimula‐

This is a relatively new area of application for hydraulic fracturing and remains in the early evaluation stage with no large scale deployment as yet. As noted in [13], hydraulic fracturing is being investigated as a means of reducing in-situ rock stress to ameliorate the frequency and

Typically such work is being performed in small diameter boreholes at high pressure but low flow rates, similar to those encountered in stress testing although more effort is made towards

What do all of these applications have in common, and how do they differ? To differentiate,

**Injectate Volume** – How much fluid is injected? Note that we could also consider injection

flow rate here although the total volume injected is clearly related to flow rate.

conventional oil and gas.

396 Effective and Sustainable Hydraulic Fracturing

**2.9. Rock burst mitigation**

severity of rock burst incidents.

propagation of the fractures.

**3. Characterization**

500,000 litres.

**2.7. Coalbed Methane (CBM) development**

(if any) additives in the fracturing fluid.

**2.8. Coal Mine Methane (CMM) drainage**

tion fractures, especially if carried out from underground.

we'll look at some of the physical aspects of fracturing:

**Fracture/NoFracture:** Are we actually creating new fractures, or simply opening existing fractures? Are there certain applications that really aren't fracturing at all?

A consideration of each of the above activities in relation to the suggested characterization criteria is given in Table 1.
