Environmental Engineering Reference
In-Depth Information
Once the surface casing is in place, the regulatory authorities may require
operators to install blowout-prevention equipment at the surface, to prevent
any pressurised fluids encountered during drilling from moving through the
space between the drill pipe and the surface casing.
The operators could also be required to completely fill the annulus with
cement from the bottom to the top of the production casing. However, there
could be reasons why full cementation is not always required, including the
fact that in very deep wells the ''circulation'' technique of filling the annular
space with cement (see previously) is more dicult to accomplish as ce-
menting must be handled in multiple stages, which can result in a poor
cement job or damage to the casing.
In some instances, well tubings are inserted inside the above casings. They
are typically of steel pipe, but they are not usually cemented into the well.
Prior to fracturing, the last step is to install the wellhead that is designed
and pressure-rated for the specific hydraulic fracturing operation. In add-
ition to proving the equipment for pumping and controlling fluid pressure,
the wellhead incorporates flowback equipment to deal with the flowback of
fracturing fluid from the well and includes pipes and manifolds connected
to a gas-water separator and tanks. Figure 4 shows a typical well site during a
single hydraulic fracturing operation.
2.1.5 Fracturing Procedure. The fracturing procedure is carried out one
well at a time, with each well having multiple stages. A multi-stage proced-
ure begins with isolating the well to be fractured and fracturing portions
of the horizontal bore, starting at the far end of the wellbore by pumping
fracturing fluid in and maintaining high pressures. The process is then re-
peated for the next section back and typically the process to hydraulically
fracture a 1.2 km horizontal bore consists of 8-13 fracture stages. The
pressures used in the fracturing process range from 5000-10000 psi. To
minimise the risk of any issues when using the hydraulic fracturing fluid,
the operator can pump water and mud into the bore to test the production
casing to at least the maximum anticipated treatment pressure. Test pres-
sures above the maximum treatment pressures can be used but they
should never exceed the casing's internal yield pressure.
The whole of the above process from construction of the access road to the
well clean-up and testing can take between 500 and 1500 days, based on the
experience in New York State as shown in Table 1. 15
2.2 Exploitation of Reserves
2.2.1 Ownership of Reserves. In the USA the onshore shale gas industry has
developed with very little in the way of public dissent. The reasons for this
include the fact that the land owner often owns the mineral rights as well.
This has resulted in many of the landowners actively encouraging explor-
ation and production as they can ensure contractual arrangements for a
 
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