One of the constant problems that is faced in cementing of oilfield well are micro annuli, and as a result, there is often reduced production and also need expensive remedial cost.
We will try to see in this post, few most common reasons for occurrence of micro-annuli and also how you can deal with them.
You must be aware of the consequences of a well that is not sealed off properly. There can be many leaking wells available on the planet which can be a big challenge in many ways.
Significant number wells are usually shut off despite there is a possibility of years of production in future. If the leakage can be stopped somehow then we can prevent the loss of revenue of Renegade Wireline service company due to production loss.
What are micro-annuli?
Due to changes in the temperature and pressure, a micro-separation is caused between pipe and the cement during the process of cementing setting or after cement is fully set. There can also be micro-annulus taking place between cement and the formation.
What are the causes?
- Cracks in the cement
Various forces may occur while setting process is going on that lead to de-bonding. Also, there will be micro fractures created in the cement. Same thing can also happen due to shrinkage of cement after some time.
- Inadequate cleaning
If the muds or any other materials present on the wall are not properly cleaned it may result in weak bonding.
- Expansion and contraction
There can always be changes in pressure or stress due to water that may result in debonding.
- The hydrostatic head
While setting the cement in certain zone there is less hydrostatic head during the formation. During setting process, high gas pressure coming from the bottom may result in migration of gas.
Finally, gas will be able to find its path through the mud cake, that result into fluid column in cement.
How you can deal with micro-annuli
Following are few things that can be done to avoid micro-annuli:
- Preventive
- Proper centralization of the casing
- Provide clearance for proper placing of cement
- Before cementing do proper hole-cleaning
- Separating cement from mud
- Efficient replacement of mud with cement.
- Remedial
After damage has taken place do the following:
- Use small-particle cement
- Ultra-fine cement may be squeezed
- Try to fill the gap and seal as much as possible
- Use low-viscosity type resin material
- It will be less prone to get bridging off. It will not lock entrance or the path for accessing.
- Usually, it is particle free and available everywhere and also you are able to pump water. This is more viable option for micro-annuli sealing off.
