This post provides additional information for those who need more detail regarding cement slurry contamination. This is a follow-up post to previous posts where we covered fluids intermixing (as in liner cementing and rheology in primary cementing).
What are the consequences of contamination?
Poor Cement Log Evaluation:
Cement log evaluations can show poor cement in Liner jobs (typically 7” or less) more commonly ranging from 3,000 to 4,500 meters in depth.
Cement slurry volumes will range from 30 to 80 bbls using only top plug even after having successfully executed cement jobs.
Gelled Contaminated Residues on Top of the Liner Hanger:
Strong contamination due to in-pipe fingering and annular channelling of the cement slurry, spacer and mud. This can be affected by the type of mud, mud salinity, density, the sufficiency of the centralization and whether the mud/hole is conditioned or unconditioned). This can lead to potentially dangerous gelled fluids/residues being left on top of the liner.
You’ll find lots of useful reference information on this table below. You may want to save it and keep it as a kind of cheat-sheet for your engineering work or studies.
|Optimized Centralization, based on: software simulation with detailed well (Survey, Caliper, ) Configuration; Fluids Definition (OBM, Spacer, Cement Slurry rheology) and ECD management (known or predicted formation pressure and FG).||High.|
|Reduction of contamination between slurry, spacer and mud by proper rheology hierarchy (mud displacement efficiency) during the Job design.||Medium to Low. It lowers as liner depth goes deeper.|
|Cement Slurry / Spacer / OBM compatibility Tests: Rheology (API), Thickening Time and SGSA (suggested contamination profile 50% Slurry + 25% OBM + 25% Spacer or based on mud displacement efficiency simulation). Actions to be taken based on results.||Medium to Low. It could be difficult and time-consuming to obtain a balance between the slurry designed characteristics for its primary purpose (safe annular placement and successful zonal isolation) and the resulting modifications performed to overcome spacer/mud incompatibility. This incompatibility can be manifested in rheology, thickening time, static gel and/or CS development.|
|Laboratory UCA test to be performed according contamination profile (select educated-worst-case scenario as per computer simulation in mud displacement efficiency). Provide contaminated slurry characteristics (Acoustic Impedance, etc.) to logging company for Cement Log Evaluation.||Medium to Low. It could be time consuming for the lab and it will only has an effect on a better understanding of the cement evaluation log.|
|Use of Saline Slurry for OBM salinity higher than 180,000 ppm (This could also be influenced by BHT and OBM density).||High to Medium. Applicability is case-specific.|
|Reduction of contamination between slurry, spacer by proper rheology hierarchy (mud displacement efficiency) during the Job design.||Medium to Low. It lowers as liner depth goes deeper.|
|Possibility of using a physical barrier (bottom plug).||High. It requires adouble-plug liner Tool system. It can reduce total slurry contamination (total contamination being, in-pipe + annular fluid mixing) in as much as 60%, specially for casing liners deeper than 4,500 meters. It could increased associated job risk related to tool failure or float equipment plugging.|
Hope that this post has been helpful to you. I run this site for free and your comments and feedback keep me going, so please let me know what you think!
Luis Lobo says
BPM…rate its important too.
Bikouyi Lekombagni says
I was going through your posts and this one remembered me some very hard time with liner’s cement jobs and particularly this contamination risks inside the pipe issue. I just want to express here that sometimes even with large volume the risk of having a poor cement log exists, maybe it is worse depending on the Well configuration.
I experienced some Liner Jobs in Mexico (Mezosoico that you know better than I do) where it was very difficult to have a good cement bond. This was the case of some long 11 7/8 in or 11 3/4 in or 9 7/8 in or 9 5/8 in liners where a huge volume is pumped. There is no need to talk about the well’s condition challenges such as lost circulation issues, MW = 1.9 – 2.0 g/cm3 or more, issues to centralize sometimes etc… So, I will focus on their configurations.
These wells are not only deep (set at +/- 5500 – 6200 m) but also long (+/- 800 – 1000 m length) that it is hard to avoid fluids contamination while traveling inside the DP and casing. This is because of the change in ID from DP to the casing while the cement is traveling inside (in-pipe /casing fingering). Even with an excellent design (centralization, fluids hierarchy, all lab tests, cement placement optimization etc…), the risk of having contaminated cement reaching the annular remains very high, of course, no need to mention the risk of having a wet shoe due to the film of mud.
We tried many times and pushed for the use the double plug system in vain due to the risks involved as you mentioned above (Deep liners, high MW etc…).
This does not mean that we did not have good results at the end, we had our learning curve. Among a large number of the lessons learned probably one of the most important was the time required to run logs to evaluate the cement. We started running logs, such as the basic CBL VDL, after weeks or months (sometimes after the next section was drilled and cemented) due to the delay in contaminated cement CS development (As per contaminated cement UCA test results). Let just say that it is easy when you have a comprehensive client because logs are not good if you only trust the non-contaminated cement CS test results.
Only a small contribution from my side because it is clear that there are so much to say about this interesting topic.
Lenin Diaz says
Thanks for your excellent contribution Bikouyi, indeed with up to 1000m liner length and 9 5/8″ to 11 7/8″ casing size in pipe contamination is expected to be a big challenge, but in your case also the annular contamination will have big role. In these cases, depending on the zonal isolation targets, the cementing design could be focused to get good cement bond towards the bottom 500m of casing, with the rest of the available space, top 500m of casing + overlap + top of LH serving as repositories for contaminated cement. However with such a heavy mud, the longer the length of targeted good cement bond towards the bottom the longer the length of contaminated cement of top of the LH. In addition, this contaminated mixture cement / mud on top of the liner hanger presenting the risk to develop high gel strength. In these cases, having a 4-arm caliper log is highly recommended.