Quite often many of the oil wells may get surface casing flow of vent followed by gas migration. This could lead to few issues as follows –
- Production interruption
- Various concerns about regulations
- Contamination of underground water as well as surface water
- Fire hazards because of gas leakage
- Greenhouse gas emissions
- Damage of reputation
Cost of repairing micro-annulus due to gas migration can increase due to many hidden reasons. Many other complications too may develop.
Due to all these complications, there may be reduced success and as a result, clients will have to pay more cost and may also lead to secondary failure of job.
Any kind of vent flow in surface casing, if detected will be an indication that gas or fluid migration and movement is taking place within the annulus. There can be many factors which may be responsible but are difficult to identify.
Lots of effort and time will be needed to identify various sources that are responsible for producing migration.
It is therefore necessary that all activities must be planned while designing cement program because damage in cement sheath can occur while placing cement and also during completion of activities during operations or production.
Therefore, all drilling engineers need to work together along with all the service companies in order to meet the various requirements right from the starting of well planning stage for making sure that you can achieve formation isolation.
Typically, gas migration will occur as gas flows via mud channels and other filter cake deposits. This can also happen when shrinkage will take place during cement transition from plastic state to hardened state.
When cement will shrink, it may pull away from mud filter cakes, and also can lose contact with casing, leaving microchannel for gas flowing through.
Even lack of seal can also allow dry gas flowing through moist channel made of mud cake to cause it getting dry and shrink, leaving even larger flow in the channel.
This can also be reduced or even prevented by either adding or using certain specific cementing materials along with an expanding agent within the cement design.
Also, while performing primary cement job properly, and also post-job analysis already has confirmed that every step of process is entirely as per the plan.
Cement seal can slowly show failure or even form internal cracks within few days or even after years of production. The reason of such deterioration is due to various stresses that is implicated on cement sheath.
While the completion of production process of the well, certain cyclic events can occur which can affect cement sheath integrity due to the effects of temperature, pressure and remediation procedures.