Well Integrity Technical Section

Good morning

This is a design/well integrity question to several technical communities since it covers a number of disciplines.
There is enormous experience in the industry, I am hoping some of the experts can provide some guidance.

In your organization, once the well is constructed.

1.       Production/Well Integrity
How do you monitor the integrity of the casing beyond the production casing. Ie the intermediate and surface casing thru out the life of the well?
Monitoring the annuli helps with identifying gas/oil/water migration but does not indicate the integrity of the actual casings.

2.       Drilling.
If the surface casing is damaged/corroded, must you abandon the well?. (as per the original mechanical well design, this is considering that the surface casing carries the weight of all the consecutive casings in the well)
Can you legally allow the cement to carry the load of the casing thru its lifespan?

3.       Drilling/Well Integrity
Does a perfect cement (based on a bond log) sheath between the casing have a lifespan? If so, how is this determined.

4.       Drilling/Well integrity
We are well aware that casing by itself does not have a long life span downhole.
Assuming a perfect cement (based on a bond log), what is the best way to assume the lifespan of the cemented casing.

We have drilled and completed 1000's of wells across the planet.
These wells are getting older and now it might be time to set some limits as to the lifespan of the wells.

------------------------------
Basker Murugappan
Principal Production Technologist
Villalbilla, Spain
+34 644485970

Three basic rules:
1) Change is inevitable.
2) Everybody resists change.
3) You cant stop change
------------------------------

Hi Basker,

A short contribution to 3 of your questions. Point 2 requires a longer discussion:

1. Annulus pressure can also detect a leak through one of the tubulars delimiting it. You will then confirm it by pressure testing (corrosion logs are there to characterize meta loss, not to find holes). A casing hole below ToC may not be detected if it leaks into an intermediate aquifer. This is why you also want to monitor production - and even more injection - to help detect leaks.

3. Cement doesn't have a life span. There is no material degradation mechanism that can jeopardize well integrity (i.e., cement has been providing zonal isolation, but now it's leaking). A possible exception may be strength retrogression above 110 degC, but I'm not totally sure. Similarly, if you ever expose your cement to temperatures >160 degC and flash pore water, you may be up for some surprises. But this is rare outside of high-enthalpy geothermal wells.

4. Good cement, i.e., no flow in the annulus, means no external corrosion. So now you have to prevent internal degradation. This can happen because of wear, erosion or corrosion. Unless you have weird form of corrosion, falling under the banner of Stress Corrosion Cracking, then a fluid with pH>=12 and full of biocide (or crude oil) may guarantee a long and happy life. Corrosion depends on basin, field, and well characteristics. For most mild conditions a well can last >70 years based on my experience. But it can also fail very quickly if you do something silly, Produced Water ReInjection for instance. 

By the way: I know with "bond" log you mean cement evaluation log. Just don't rely on CBL (THE bond log) to assess cement integrity.

Excellent topic,

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Matteo Loizzo
Well integrity consultant
matteo.loizzo@mac.com
Berlin, Germany
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Hi Basker,

Relevant questions... some might remain unanswered actually (or at least without a simple statement for a reply)

1.      Production/Well Integrity
How do you monitor the integrity of the casing beyond the production casing. Ie the intermediate and surface casing thru out the life of the well?
Monitoring the annuli helps with identifying gas/oil/water migration but does not indicate the integrity of the actual casings.

Magnetic response tools can be used to provide some info on the overall condition on casing strings beyond the production casing. I have limited experience with this but basically found out that: 1- the response is an average one and will work well for gradual WT loss  / corrosion but won't necessarily give useable info for very localized issues; 2- this is still a valuable info; 3- it would work best if a baseline log had been acquired previously (so tracking only the changes would be easier); 4- very few operators will volunteer to run these logs unless regulations call for them (sadly... but you'll be fully familiar with this).

Breakthroughs in Ultrasonic logging tools & processing could happen... but at the moment multi-string data remains challenging (Cereus seems to be offering interesting solutions in that space...)

2.       Drilling.
If the surface casing is damaged/corroded, must you abandon the well?. (as per the original mechanical well design, this is considering that the surface casing carries the weight of all the consecutive casings in the well)
Can you legally allow the cement to carry the load of the casing thru its lifespan?

Interesting case. I'd split this between onshore and offshore issues, really... Did you have specific cases in mind? I can see at least the following cases to guide a discussion:

Land wells: there are cases where a CP can be eroded by rain flow and gradually loose its supporting function... In such cases and where access to a cellar would still be possible there may be mitigating measures, such as using jacks, taking some weight again and resting it on a new structure... or repeating a top job with cement. If you have in mind a scenario where shallow corrosion (salty water for instance) can compromise both the CP and the surface casing... then you are left with a structural issue potentially compromising your pressure-containing envelopes

Offshore surface: there the CP usually has a structural role also... you cannot fail the CP without potentially buckling your surface casing, potentially compromising pressure envelopes. Monitoring can be done but often falls in-between departments (this is still happening...). Ie. the structural integrity team is keeping track of the structure... and the wells team is keeping track of the pressure-containing envelopes... but not the CP's (which might require shallow ROV or diver inspections).

This will become even more critical for potential repurposing of offshore surface wells for CCS applications where injection of a cold stream can result in thermal shrinkage of tubulars and significant additional compression (2H presented a case in June at the Wells Decom event in Aberdeen)

Subsea: there you'd most likely have to assess by how much a string may have dropped (WH elevation drop as well... that's why mud-mats were used to allow taking on weight until full curing of the cement...)

For your exact question re: allowing cement to "carry the weight" I would say yes to an extent, as long as engineering assumptions are correct.

3.       Drilling/Well Integrity
Does a perfect cement (based on a bond log) sheath between the casing have a lifespan? If so, how is this determined.

I'd offer a different response to Matteo's and say clearly not... So many things can happen during the life-cycle of wells that on top of environmental factors there are also user-imposed loads! If a well was successfully cemented initially and left alone, then good cement should in practice isolate (and protect) casing from corrosion. But then add to this multiple thermal cycles, fracturing, depressurizing, etc... and your initial good bond may become compromised. If this happens (and your cement cracks for instance) then there could be corrosion, or pressure transmission like in the case of SCP or SCVF

4.       Drilling/Well integrity
We are well aware that casing by itself does not have a long life span downhole.
Assuming a perfect cement (based on a bond log), what is the best way to assume the lifespan of the cemented casing.

Broad question... would deserve to be broken down for more accurate answers. In a perfect world the cement-steel-cement sandwich has until now been considered "good" (ie. constituting a competent pressure barrier) in perpetuity (with what we have been pragmatically being an arbitrary 1000yr criteria). Change that and introduce cracks or fluid flows, and this becomes an engineering question: what can be the evolution based on what we know of a specific situation? For this we'd need more data to answer a question about the "lifespan of a cemented casing". The cement in isolation is something different. And if you wanted to consider this integrity issue for P&A and repurposing (in particular CCS) then it would be better to consider the performance of an entire "barrier" - this should use a systems approach on all components (rock/caprock, fluids, cement and casing) and their interfaces.

Hello Basker,

1. generally at the time of the identification of the well technical scope we ensure installation of real time monitoring on all annuli for dry trees (onshore and platform), and only A-annulus (between the tubing and the production casing), B-annulus is generally designed with the shoe as the weakest point, C- and onwards are generally cemented to surface. The technology to wirelessly monitor B-annulus for offshore wells was developed in 2011, but is not yet widely used. Though at some stage it was expected that it will become mandated by the regulator in some selective countries, like Norway and UK. If the continuous monitoring is not available, the frequent pressure check is done manually by operators and entered into the single repository. Annulus pressure is the first indication of whether issues occur or not. Frequent corrosion logging (USIT, defectoscope etc.) are strongly recommended and generally ran on onshore wells. Offshore wells try to mitigate corrosion by material selection, inhibitors etc. Use of corrosion inhibitors, oxygen scavenger, refill the annulus to surface to avoid oxygen ingress and "splash-zone" corrosion are key. If we have alkaline soils or have aquifers, we intend to paint casings prior to running them.

2. Is the casing is damaged/corroded, whether you can continue production or not depends on a lot of factors: whether you have permeable zones, what they are filled up with, whether you can open the fracture to surface, and other external leak risks etc. Grouting can help expend the life of the well, as well as application of BiSN and some similar technologies. If the weight is a concern, a collar with the weight distribution on some construction/ structure can take off the weight of the well. Again, you need to make sure that the risk of the well is ALARP for people, environment, reputation/community etc. 

3. Cement has a lifespan. The actual life span depends on the dynamic load the well experiences during the lifetime. So, if varies with temperatures, rates, and their variations. But if you have at least 2x30 m of good quality cement, you should generally be ok for the lifetime of the well. 

regards,

Ksenia

Hello Basker, 

I would try to provide you with some of my insights hoping that it will give you some perspective in terms of how to manage well integrity risks associated with loss of containment or loss of access to the well. 

First of all, you have to do a proper risk assessment for all the hazards associated with each barrier in your system. In addition, you have to look at hazards associated when two or more of those barriers failed simultaneously. Once you identified the risk levels, you have to decide how you can mitigate those. First action is proper design but sometimes this is not possible due to technology limitations or cost implications. Second is monitoring options. Depending on the severity of the hazard, you have to identify what to monitor, how to monitor and how often to monitor. Also, by doing a through investigation, you might have an idea about key indicators that increase the risk for some of the wells and might prefer to allocate your efforts and cash to investigate those wells. 

Thanks for all the feedback,  both via the forum and privately.
Specifically for land wells

Most of the recommendations was centered around monitoring the annulus between the casings. This is currently being done in real-time, so pressure testing, sampling and monitoring pressure buildup is normal practice.

Logging behind the production casing (ie intermediate, surface casing), we have tried lots of tools, no much success here. We can safely (relatively) determine the status of the production casing and cement sheath but any cement sheath/casing status beyond the production casing becomes a hand waving exercise. In a nutshell, over the lifespan of the well, we can only be sure of the status of the production casing and its cement sheath with current technology logging tools.

The status of the remaining casing's integrity (not cement sheath) is questionable. We can use CP in the surface casing but we have no idea what is its effectiveness. We have no method to measure this thru multiple casing strings.

Several comments from this group: It does not matter if the surface/intermediate casing has been completely corroded, what matters is the integrity of the cement sheath in the anuli and the last production casing (and its cement sheath). So basically, don't worry about it, let the casing's corrode completely, it's the last (production) casing and cement sheath that is critical.
Interesting, way of looking at it. So basically after well construction phase, don't worry about the other casing, they are disposable.

Summarizing, all the comments. The well lifespan in unlimited as long as

1.     Production casing and its cement sheath has integrity

2.     The cement sheath in between all the casing annuli has integrity

If we go down this path, it definitely does significantly simplify the well lifecycle integrity analysis.
A good cement sheath will last +2000 years (Matteo et al), so this basically drives us to the conclusion that our flowing and P&A wells would last almost forever?

------------------------------
Basker Murugappan
Principal Production Technologist
Villalbilla, Spain
+34 644485970

Three basic rules:
1) Change is inevitable.
2) Everybody resists change.
3) You cant stop change
------------------------------

Hello Basker,

CP in land wells generally good for 120 m of so. Below it will be unreliable due to the amount of factors which can influence.
I forgot to mention in my previous reply, that if you use ESPs or have high voltage cables around, please, make sure they are all earthed and the darting is done correctly to avoid corrosion.

if your casing was protected by cement, it should generally be ok. Any open surfaces, could be inspected. There are a number of pulsed eddy current tools and even boroscope cameras (access permitting). 
For the abandonments, we cannot say we are good "forever". If the site is accessible it would be good to check it once eventually 5 years or so. If you placed enough cement (ca. 100 m good bonding), squeezed the reservoir, verified good seal integrity or established one, cut and pulled parts of casing and placed additional shallow isolations, you should be good. 

regards,

Ksenia

Original Message:
Sent: 10-08-2023 06:35 PM
From: Basker Murugappan
Subject: Several questions of well design and Integrity

Thanks for all the feedback,  both via the forum and privately.
Specifically for land wells

Most of the recommendations was centered around monitoring the annulus between the casings. This is currently being done in real-time, so pressure testing, sampling and monitoring pressure buildup is normal practice.

Logging behind the production casing (ie intermediate, surface casing), we have tried lots of tools, no much success here. We can safely (relatively) determine the status of the production casing and cement sheath but any cement sheath/casing status beyond the production casing becomes a hand waving exercise. In a nutshell, over the lifespan of the well, we can only be sure of the status of the production casing and its cement sheath with current technology logging tools.

The status of the remaining casing's integrity (not cement sheath) is questionable. We can use CP in the surface casing but we have no idea what is its effectiveness. We have no method to measure this thru multiple casing strings.

Several comments from this group: It does not matter if the surface/intermediate casing has been completely corroded, what matters is the integrity of the cement sheath in the anuli and the last production casing (and its cement sheath). So basically, don't worry about it, let the casing's corrode completely, it's the last (production) casing and cement sheath that is critical.
Interesting, way of looking at it. So basically after well construction phase, don't worry about the other casing, they are disposable.

Summarizing, all the comments. The well lifespan in unlimited as long as

1.     Production casing and its cement sheath has integrity

2.     The cement sheath in between all the casing annuli has integrity

If we go down this path, it definitely does significantly simplify the well lifecycle integrity analysis.
A good cement sheath will last +2000 years (Matteo et al), so this basically drives us to the conclusion that our flowing and P&A wells would last almost forever?

------------------------------
Basker Murugappan
Principal Production Technologist
Villalbilla, Spain
+34 644485970

Three basic rules:
1) Change is inevitable.
2) Everybody resists change.
3) You cant stop change
------------------------------

Good afternoon Basker, 

Please see below my answers: 

1. production well integrity: we can close monitor the integrity of tubing and casing beyond using Corrosion log and there many services companies that provide the technologies. the challenges is to have a good correlation with the gamma ray/ CCL logs provided after drilling with the corrosion logs for a good interpretation result and remediation/ mitigation plan. tubing and casing materials sure that it will degrade over time depending on many circumstance ( corrosion/erosion it is why we have to manage it, for the surface  /intermediate casing all annuli should equipped with Pressure Gauges and closely monitored, if there is any annulus pressure in the annulus, an investigation must be carried out in order to determine the source of the pressure where is coming? from reservoir or other sources, taking samples is required to see if the fluid is corrosive. we have to set for each annulus a Maximum operating annulus pressure (MOAP) and Manage it,  ISO 16530-2 and API RP 90 demonstrate how to calculate and recalculate the MOAP each Year.
2. Driiling: Thee surface casing shall be cemented to the surface to take advantage of and additional strength and lateral stability and slow down the internal corrosion. during the life cycle of the well the external & internal corrosion should be managed b by operators but if and severe external corrosion the surface casing is occurred than  a structural risk assessment must be carry out and categories the wells, if the Risk is high the well shall be repaired immediately. several repair method have been identified like: Welded sleeve clamps and I-beam. 
3. Drilling/well integrity:  having a good cement bond a long a section is lucky but the cement is designed unlimited lifespan. we can approve to continue drilling the next section even we have a poor cement bond in some depth, we can manage a producer well with a sustained casing pressure due to a bad cement, but how we can manage it if we plug and abundant the well, ok we can manage only at surface with gauges, but what if the cement fail. your question can be a good subject of research we start from data analysis, here all operators shall be involved and provide there historical data, if it is proven that a leak was occurred after P&A. I know that is catastrophic but it will be good reason to enhance and improve the studies on cementing.