Well Integrity Technical Section

You could consider fibre optic surveys to confirm if there is currently isolation. Fibre deployed through tubing or production casing utilises Distributed Acoustic Sensing (DAS) to detect leak paths across all casing and annuli. The company I work for is Well-Sense which provides disposable fibre optic services to ADNOC. There are wireline service providers that provide similar options using fibre in slickline or fibre in wireline. 

Once you confirm what communication there is, or is not, behind the 13-3/8" casing then remediation is another topic

I'm talking about the abandonment of well with 3 cemented casing strings. is it possible to run your proposed survey to read cement integrity behind third casing. I'm aware about double barrier cement evaluation but not sure about third barrier.

You could consider fibre optic surveys to confirm if there is currently isolation. Fibre deployed through tubing or production casing utilises Distributed Acoustic Sensing (DAS) to detect leak paths across all casing and annuli. The company I work for is Well-Sense which provides disposable fibre optic services to ADNOC. There are wireline service providers that provide similar options using fibre in slickline or fibre in wireline. 

Once you confirm what communication there is, or is not, behind the 13-3/8" casing then remediation is another topic

I'm talking about the abandonment of well with 3 cemented casing strings. is it possible to run your proposed survey to read cement integrity behind third casing. I'm aware about double barrier cement evaluation but not sure about third barrier.

You could consider fibre optic surveys to confirm if there is currently isolation. Fibre deployed through tubing or production casing utilises Distributed Acoustic Sensing (DAS) to detect leak paths across all casing and annuli. The company I work for is Well-Sense which provides disposable fibre optic services to ADNOC. There are wireline service providers that provide similar options using fibre in slickline or fibre in wireline. 

Once you confirm what communication there is, or is not, behind the 13-3/8" casing then remediation is another topic

Hi Mostafa,

You write that you're uncertain about zonal isolation. 13⅜" casing is normally shallow enough that you have direct communication with the wellhead, especially if you had substantial losses. So the first step would be to verify if you have integrity or not: are you producing anything (brine I presume)? If so, what is the leak rate?

The next step would be to have a stab at the leakage pathway: if it's 1-100 tons per year it's a microannulus. If 10,000 tons per year or more, then it's a large defect, like empty annulus, mud channel or chimney.

Since you're abandoning, you don't necessarily care about casing corrosion so you will choose the repair method more appropriate for the size of the pathway:

• If the annulus is open (or you have a channel), then a top-up cement job of some sort should be good enough. Just engineer thixotropy and add fibers to ensure you don't try and fill a large loss circulation zone. May as well bullhead LCM pills before pouring your cement.
• If it's a chimney, then you need to pump resin or micro cement. Slowly. There are simple diagnostic methods.
• If it's a microannulus then you want to pump a low-viscosity resin under as high pressure as possible. May end up doing 2-3 jobs, but it should be straightforward.

Mind that if you have no evidence of a leak, and if a leak would show up at the top of the annulus (e.g., if ToC is below the previous casing shoe), then you're isolated.

Best regards,

Hi Matteo

The 13 3/8 is set at around 10,000 ft and previous shoe at 2000 ft. The cement job had no returns, and we know the losses zone behind the casing. However, pressure sustained at zero psi for 40 years. Regulatory wise, there is no lateral cement isolation (rock to rock). all casings are cemented even 7'' so cutting and pulling will be difficult). Target cap rocks to perform remedial located at 2500, 5000, 7000 ft.

is performing injectivity test to annulus to ensure isolation from surface up to 200 psi (for example) would be enough and accepted? or we need to go the hard option of double casing milling and then perforate third casing. May be triple casing milling? What do you think?

Hi Mostafa,

You write that you're uncertain about zonal isolation. 13⅜" casing is normally shallow enough that you have direct communication with the wellhead, especially if you had substantial losses. So the first step would be to verify if you have integrity or not: are you producing anything (brine I presume)? If so, what is the leak rate?

The next step would be to have a stab at the leakage pathway: if it's 1-100 tons per year it's a microannulus. If 10,000 tons per year or more, then it's a large defect, like empty annulus, mud channel or chimney.

Since you're abandoning, you don't necessarily care about casing corrosion so you will choose the repair method more appropriate for the size of the pathway:

• If the annulus is open (or you have a channel), then a top-up cement job of some sort should be good enough. Just engineer thixotropy and add fibers to ensure you don't try and fill a large loss circulation zone. May as well bullhead LCM pills before pouring your cement.
• If it's a chimney, then you need to pump resin or micro cement. Slowly. There are simple diagnostic methods.
• If it's a microannulus then you want to pump a low-viscosity resin under as high pressure as possible. May end up doing 2-3 jobs, but it should be straightforward.

Mind that if you have no evidence of a leak, and if a leak would show up at the top of the annulus (e.g., if ToC is below the previous casing shoe), then you're isolated.

Best regards,

Hi Mostafa,

Since you mention more than one caprock, is that because you have a risk of flow between different formations?

Mind you that there should be a valid reason for imposing isolation, such as resource pollution (say, contamination of a drinking water aquifer, or depletion of a high-pressure brine source), rather than a generic wish from Regulators to restore initial caprocks. Further to this point, it's not because you have an impermeable layer in a well that large aquifers are isolated, and shallow wells have been a less reliable barrier than deep O&G ones: would it make sense to go out of your way to seal a well when a dozen more are happily flowing in the neighborhood?

NORSOK D-010 Rev.5 is far less clear on isolation requirements than previous versions, requiring us to document "management of undesirable crossflow". OEUK Well Decommissioning Guidelines section 2.5 do not require isolation if the risk of crossflow is acceptable.

As for qualifying barrier elements, evidence of integrity other than logs or "displacement calculations" cannot rely on NORSOK D-010, but you can use the longer list of criteria proposed by OEUK WDG, section 4.3.

So, we have two scenarios: either you have a single source of inflow to surface, or an (undetectable) crossflow between aquifers.

• With a single source of inflow, no sustained pressure is probably good enough (at least for OEUK WDG). The injectivity test you propose is a good idea: no returns doesn't mean that we have no cement, but rather than we don't know how high it got.
• Since crossflow may not be detectable from surface, then I would suggest a simple temperature log to confirm it - as long as the two aquifers are far enough apart. If a temperature anomaly is possible but none is found, then we can conclude that we're isolated. I'm not sure that noise can detect crossflow between carbonates, but local wireline companies may know. It's worth a try.

Restoring isolation in the case of a single source of inflow can be done by bullheading, followed by pressure testing. That should be good enough.

In the case of multiple horizons you may try a funny type of coiled tubing proposed by Expro: the idea is to cement bottom-up, possibly with periodic verifications (intermediate tagging and pressure testing after the top permeable formation).

Best regards,

Hi Matteo

The 13 3/8 is set at around 10,000 ft and previous shoe at 2000 ft. The cement job had no returns, and we know the losses zone behind the casing. However, pressure sustained at zero psi for 40 years. Regulatory wise, there is no lateral cement isolation (rock to rock). all casings are cemented even 7'' so cutting and pulling will be difficult). Target cap rocks to perform remedial located at 2500, 5000, 7000 ft.

is performing injectivity test to annulus to ensure isolation from surface up to 200 psi (for example) would be enough and accepted? or we need to go the hard option of double casing milling and then perforate third casing. May be triple casing milling? What do you think?

Hi Mostafa,

You write that you're uncertain about zonal isolation. 13⅜" casing is normally shallow enough that you have direct communication with the wellhead, especially if you had substantial losses. So the first step would be to verify if you have integrity or not: are you producing anything (brine I presume)? If so, what is the leak rate?

The next step would be to have a stab at the leakage pathway: if it's 1-100 tons per year it's a microannulus. If 10,000 tons per year or more, then it's a large defect, like empty annulus, mud channel or chimney.

Since you're abandoning, you don't necessarily care about casing corrosion so you will choose the repair method more appropriate for the size of the pathway:

• If the annulus is open (or you have a channel), then a top-up cement job of some sort should be good enough. Just engineer thixotropy and add fibers to ensure you don't try and fill a large loss circulation zone. May as well bullhead LCM pills before pouring your cement.
• If it's a chimney, then you need to pump resin or micro cement. Slowly. There are simple diagnostic methods.
• If it's a microannulus then you want to pump a low-viscosity resin under as high pressure as possible. May end up doing 2-3 jobs, but it should be straightforward.

Mind that if you have no evidence of a leak, and if a leak would show up at the top of the annulus (e.g., if ToC is below the previous casing shoe), then you're isolated.

Best regards,

Hi Matteo. Yes, regulatory wise, 150 ft of lateral cement isolation is required. I personally see pressure test is enough but also the point that permanent P&A and no further monitoring means following the standard as per the book is the safest course. 

Hi Mostafa,

Since you mention more than one caprock, is that because you have a risk of flow between different formations?

Mind you that there should be a valid reason for imposing isolation, such as resource pollution (say, contamination of a drinking water aquifer, or depletion of a high-pressure brine source), rather than a generic wish from Regulators to restore initial caprocks. Further to this point, it's not because you have an impermeable layer in a well that large aquifers are isolated, and shallow wells have been a less reliable barrier than deep O&G ones: would it make sense to go out of your way to seal a well when a dozen more are happily flowing in the neighborhood?

NORSOK D-010 Rev.5 is far less clear on isolation requirements than previous versions, requiring us to document "management of undesirable crossflow". OEUK Well Decommissioning Guidelines section 2.5 do not require isolation if the risk of crossflow is acceptable.

As for qualifying barrier elements, evidence of integrity other than logs or "displacement calculations" cannot rely on NORSOK D-010, but you can use the longer list of criteria proposed by OEUK WDG, section 4.3.

So, we have two scenarios: either you have a single source of inflow to surface, or an (undetectable) crossflow between aquifers.

• With a single source of inflow, no sustained pressure is probably good enough (at least for OEUK WDG). The injectivity test you propose is a good idea: no returns doesn't mean that we have no cement, but rather than we don't know how high it got.
• Since crossflow may not be detectable from surface, then I would suggest a simple temperature log to confirm it - as long as the two aquifers are far enough apart. If a temperature anomaly is possible but none is found, then we can conclude that we're isolated. I'm not sure that noise can detect crossflow between carbonates, but local wireline companies may know. It's worth a try.

Restoring isolation in the case of a single source of inflow can be done by bullheading, followed by pressure testing. That should be good enough.

In the case of multiple horizons you may try a funny type of coiled tubing proposed by Expro: the idea is to cement bottom-up, possibly with periodic verifications (intermediate tagging and pressure testing after the top permeable formation).

Best regards,

Hi Matteo

The 13 3/8 is set at around 10,000 ft and previous shoe at 2000 ft. The cement job had no returns, and we know the losses zone behind the casing. However, pressure sustained at zero psi for 40 years. Regulatory wise, there is no lateral cement isolation (rock to rock). all casings are cemented even 7'' so cutting and pulling will be difficult). Target cap rocks to perform remedial located at 2500, 5000, 7000 ft.

is performing injectivity test to annulus to ensure isolation from surface up to 200 psi (for example) would be enough and accepted? or we need to go the hard option of double casing milling and then perforate third casing. May be triple casing milling? What do you think?

Hi Mostafa,

You write that you're uncertain about zonal isolation. 13⅜" casing is normally shallow enough that you have direct communication with the wellhead, especially if you had substantial losses. So the first step would be to verify if you have integrity or not: are you producing anything (brine I presume)? If so, what is the leak rate?

The next step would be to have a stab at the leakage pathway: if it's 1-100 tons per year it's a microannulus. If 10,000 tons per year or more, then it's a large defect, like empty annulus, mud channel or chimney.

Since you're abandoning, you don't necessarily care about casing corrosion so you will choose the repair method more appropriate for the size of the pathway:

• If the annulus is open (or you have a channel), then a top-up cement job of some sort should be good enough. Just engineer thixotropy and add fibers to ensure you don't try and fill a large loss circulation zone. May as well bullhead LCM pills before pouring your cement.
• If it's a chimney, then you need to pump resin or micro cement. Slowly. There are simple diagnostic methods.
• If it's a microannulus then you want to pump a low-viscosity resin under as high pressure as possible. May end up doing 2-3 jobs, but it should be straightforward.

Mind that if you have no evidence of a leak, and if a leak would show up at the top of the annulus (e.g., if ToC is below the previous casing shoe), then you're isolated.

Best regards,