• Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Primary Cementing
  • Remedial Cementing
  • Plug Cementing
  • Job Execution
  • Post-job results interpretation
  • Equipment
  • Laboratory
  • Mission
  • About
  • Contact and Questions?
  • My Cementing Challenges

Better Well Cementing for ALL

The Leading Online Support Hub for Better Oil Well Cementing.

Mud Displacement, the ‘mystery’ factor in gas and fluids migration

January 11, 2018 By Lenin Diaz 4 Comments

Mud Displacement, the ‘mystery’ factor in gas and fluids migration

Very often I find myself helping people having issues with fluids migrating following primary cementing. In all these cases, it is always fascinating to see the frequency of this problem nowadays. Especially with the involvement of expert services companies and the availability of state-of-the-art engineering and products solutions.

I have already written here about fluid and gas migration, and this is definitely not a new topic in our industry.

More importantly gas and fluids migration should not be a ‘mystery’ nowadays. However, in some cases, it appears to be.

The cause is univocally simple:

Fluids migrate because the annulus is in underbalance

Why?

First, let’s remove the obvious triggers:

  • Losses.
  • Faulty or unknown actual Pore Pressure profile or model.
  • The next thing is the cement slurry transition period. (The intermediate self-supported gelled structure that lowers the cement slurry internal pressure to water density). NOTE: What is not so obvious, is that the conditions (let’s forget about having a proper slurry able to control gas migration or not) for this to happen are: 1) flow through the cement slurry should be the only (easiest) path (which translates to good cement coverage) for gas migration, and; 2) the cement slurry setting process actually happens.

If we remove the above, the only thing remaining is merely to achieve the main objective of primary cementing. Not only to prevent gas and fluids migration but in general for any casing cementing operation:

Cement Coverage (mud displacement)

This is the real challenge today.

In most primary cementing jobs, not achieving cement coverage (mud displacement) ends in a bad cement log and/or a lack of zonal isolation. This is already bad enough, but when there is a risk of gas or fluids migration, it might end up in a well control situation.

Why can a lack of cement coverage (channelling) lead to gas or fluids migration?

NOTE: This is what you really need to worry about in the first place. So, please do not ask for LATEX or some other specialty (costly) chemical and think that you are covered… Well, you are NOT. What you need to ask first to your cementing company is: Channelling prevention, please.

Why?

  1. Minimum ECD below Pore Pressure. This is the case when a Newtonian fluid is introduced (because the ‘best practice’ says so – supposedly!). Here the Newtonian fluid does what it does best: It channels. Then depending on the length of the channel, the fluid column becomes underbalanced during the job allowing formation fluids to enter. Then, this lowers the hydrostatic pressure even further.
  2. Damaged fluids properties:
    • Mud. Longer cement channels lead to increased cement – mud contamination (intermixing). Cement, an active contaminant for WBM, leads to loss of mud properties such as rheology (flocculation) and carrying capacity. Finally a reduction in density will occur.
    • Cement. Cement-mud contamination delays the setting process of the cement slurry. This not only prevents the formation of the gelled structure (forget about your gas migration slurry), but it might stop the cement slurry setting entirely. And what happens if the cement doesn’t set? What happens is that; Solids (cement particles) settling, and lighter fluids (water) floating. Together, these effects eventually lower the annulus hydrostatic pressure. This will allow formation fluids migration.
    • Don’t forget about cement slurry density control. One of the requisites for gas migration control slurries is Zero free-water. However, if a sufficiently large volume of cement slurry is mixed at a lower-than-designed density, the free-water increases. The result might be a destabilization of the cement slurry. This leads to loss of density in both the cement slurry and the mud.
    • The mixing of two successive fluids may lead to the formation of a viscous mixture. The viscosity of the mixture is often higher than the average viscosity of the two fluids. In turn, this increased mixture viscosity is known to be an undermining factor for mud displacement.
  3. Mud Displacement. Intermixing of Mud-Spacer-Cement Slurry or Spacer-Lead-Tail slurry. Intermixing causes a deterioration of fluid’s rheology and density. This is not accounted for by any software simulation, (assuming perfect piston-like displacement), hence leading to an obsolete hydraulic program. (Actual dynamic and static pressures may be different from the predicted model). Potentially such a program is unable to fully displace mud and/or remove gelled/partially dehydrated (filter cake-like stuff) mud.

 

In summary
  • Cement placement is fundamentally the most important gas and fluids migration objective.
  • Two main defects arise from channelling (in the case of gas and fluids migration this can be potentially dangerous) in primary cementing.
    • An un-displaced fluid. This is when a fluid is left behind, either in static (gelled mud attached to casing or formation) or flowing mode. (Typically in the annulus).
    • Fluids intermixing. Active mixing of fluids resulting in mixed-products having different properties from the individual mixed fluids. It can happen both inside the casing and in the annulus.
  • When gas or fluids migration is a risk, the main focus is to design and deploy a cement program that avoids any form of channelling. In other words, a cement program that seeks to attain the maximum possible cement coverage. Then, secondarily is the cement slurry gas migration control property (in the case of gas).

If you have any comments or questions, please contribute here.

Cheers

L. Diaz

Related posts:

  1. Gas Migration: 5 Truths (Primary Cementing)
  2. Gas migration and surface casing vent flow (SCVF) issues and prevention
  3. Workover Cementing Techniques 2: Squeeze Cementing
  4. Primary Cementing Checklist (Customer)

Filed Under: Primary Cementing Tagged With: fluids migration, gas, primary cementing, well control

Article Posted By:

Lenin Diaz is an oil industry specialist with 26 years of technical and operational expertise in fluids, cementing, water control and shut-off. A distinguished track record spanning BP, Schlumberger, and NAPESCO. Lenin lives in Tenerife, Spain and is the creator of this website. Read More…

Reader Interactions

Comments

  1. Djilali Sahnoun says

    January 28, 2018 at 1:15 pm

    Lenin
    I read through your article , very interesting topic that oil and gas companies are facing whether in primary or in remedial cementing
    I have published some work on gas migration and surface casing vent flow cause and prevention , check the SPE # 168264 I will summarize the findings later on
    Good work and best regards

    Reply
    • Lenin Diaz says

      January 28, 2018 at 1:18 pm

      Thanks Djilali, Looking forward to read more of your work and experiences here
      Cheers
      L. Diaz

      Reply
  2. moussa says

    February 23, 2020 at 5:46 am

    Hello Lenin,
    I read through your article , very interesting topic.
    in addition cement recipe play a role very important to avoid gas migration like adding a gas block or gas stop.

    Thanks

    Reply
    • Lenin Diaz says

      February 23, 2020 at 9:16 am

      Hi Moussa,
      Thanks again for your contribution to this blog.
      Please home page, left there is search option.

      Cheers
      L. Diaz

      Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Primary Sidebar

Trango DEPM is a team of Oil&Gas professionals with broad experience in the O&G industry. Working on onshore and offshore projects around the world, including most vivid and challenging areas as Saudi Arabia, US Marcellus shale and North Sea, but also small on small projects, requiring individual approach, we are well equipped to help you plan, budget, implement and execute your drilling project successfully. We also cooperate with number of other professionals with experience in such areas as drilling, geology, geophysics, procurement or logistics. This allows us to fully run your project or just support you in desired areas of expertise, depends on you needs.

How I survived the 2016 Downturn and the current difficult times?

Find the content you need

Archives

24 Page Free Primary Cementing Guide

Click this image to take a look. It is comprehensive and easy to follow too!

In 2016, I launched Better Cementing for All. Now, I want to keep it alive.

For more than 26 years, I have worked in oil well cementing, offering my services to some of the largest oil corporations in the world and committing myself to excellence. I have mastered my role, and in doing so, I have accrued a skill set that is extremely valuable to my fellow professionals. Eager to do whatever I can to help them, I have owned and operated Better Cementing for All since 2016.
Let me tell you what Better Cementing for All does and what it means. A resource for all oil industry professionals and for cementers both established and prospective, this is a non-profit resource that I established in order to do nothing but serve and make an impact on people who are looking to build careers for themselves in cementing.
From primary cementing to remedial cementing to plug cementing to post-job results, I do it all, and I am comfortable answering in-depth questions about each and every one of these topics. I also offer tools and tips for jobseekers, general self-development advice, and guidance for equipment choices. TO put it simply, this is the go-to spot for anyone who wants to know anything about oil well cementing.
The problem, however, is that covid-19 has made the structure of the website seem untenable. I am trying to juggle the work that I do and my non-profit initiatives and finding it all unhealthy and unsustainable. I want to keep Better Cementing for All up and running, but to do that, I need your help.


My NEW introductory VIDEO

Recent Posts

Max Out Your Cement Coverage

If we consider the main variables to ensure proper mud in hole replacement with cement: stand-off, … [Read More...] about Max Out Your Cement Coverage

Cementing Flowchart

In recent weeks, I received some reader requests to include cement job processes or procedures as … [Read More...] about Cementing Flowchart

Cementing. Challenges across permeable zones

This article will provide you with some actionable suggestions for cementing across permeable zones. … [Read More...] about Cementing. Challenges across permeable zones

Forensic Cementing

Forensic is a term usually associated with crimes. Criminal forensics is the use of science to … [Read More...] about Forensic Cementing

Cement Slurry design Basics

First, here is a handy table to simplify the process of cement slurry design: Additive … [Read More...] about Cement Slurry design Basics

well cementing pre-job cement challenge question

Remedial Cementing with Coiled Tubing (animation)

Though I am far from being an animation expert, during my training courses I have always wanted to … [Read More...] about Remedial Cementing with Coiled Tubing (animation)

Need urgent help?

WhatsApp me at this number: +34 657 07 01 78

Footer

Recent activity

Visit our latest posts and help others by adding a comment.

Make your contribution and help keep Better Cementing for All alive!

Now more than ever, we are facing a loss of expertise in our industry, and Better Cementing for All is a unifying force, featuring interactions among industry professionals, knowledge sharing through posts, and other valuable pieces of content that we need to preserve.

Recent Comments

  • Merit on Cementing Equipment from Serva SJS Limited
  • Lenin Diaz on Cementing Equipment from Serva SJS Limited
  • Lenin Diaz on All you need to know about Bentonite in Cement Slurries
  • Lenin Diaz on Cementing Equipment from Serva SJS Limited
  • Lenin Diaz on Cementing Equipment from Serva SJS Limited
  • Lenin Diaz on Suicide Squeeze Cementing: risky but valid
  • Samuel Bekele Bedjiga on All you need to know about Bentonite in Cement Slurries

Recent Posts

  • Max Out Your Cement Coverage
  • Cementing Flowchart
  • Cementing. Challenges across permeable zones
  • Forensic Cementing
  • Cement Slurry design Basics
  • Remedial Cementing with Coiled Tubing (animation)
  • Plug and Abandonment Webinar (Español)
  • Webinar series (II). Quality Assurance in Cementing Operations (Spanish)
  • Webinar series (I). Log interpretation (Spanish)

Submit your email

&middot Better Well Cementing For All is owned by L. Diaz © 2023 &middot TOS & Privacy Policy &middot Web Design &middot