More technically, referred as an application of circulating squeeze.
In a circulating squeeze, cement slurry is “forced” to flow through a lower open path and up behind the casing with returns being taken back into the wellbore or to the annulus. Normally, there is an isolation tool, a cement retainer or a packer placed above the lower opening. Some examples are: a) an attempt to complete casing cementing following incomplete primary cementing, an emblematic example is the second stage of a failed two stage cement job. In this case, a cement retainer is placed above the stage tool ports (if open) or a perforated interval. Fluid returns are taken to surface and in some occasions, pressure permitting, cement is returned to surface; b) remediate an impeded liner cementing operation. If a liner top packer is not in place or set, a cement retainer (better choice) or a packer is placed somewhere above the landing collar. Fluid returns to the top of the liner and cement top is characteristically kept within the overlap between casings or simply above a zone of interest; c) another example, now in remedial cementing, a cement retainer or a packer is placed in between two purposely-made perforated intervals with the intention to reinstate zonal isolation in a section of interest behind the casing.
When a packer is used in the example described in (c) the possibility of some costly consequences, catastrophic in nature, is significantly increased (impact + probability = risk). The worst of these consequences being losing the well entirely or a section, in a more theatrical way “wasting” the well, but because we love what we do and constructing the well is what justify our existence, we feel like “we are the well”, hence the “suicidal” connotation. Consequently, this circulating squeeze application in remedial cementing is what is known as “suicide squeeze”, but why is this a high-risk operation? Or more importantly, why do it?
Now because I am a cementer, answering the first question is more appealing to me, so let’s start by answering this.
First of all, for this method the conventional squeeze theory, where squeeze cementing is basically a filtration process that occurs while placing cement slurry into a wellbore entry point (leaks in the casing/wellbore) under differential pressure forcing the slurry against a permeable media causing solid cement particles to filter out cement liquid phase (filtrate) on the formation face until re-establishing isolation (node formation), does not apply because in a circulating squeeze the objective is not to form a cement cake or node but to fill a channel or large void behind the casing with cement slurry.
During a “suicide squeeze” as an application of the circulating squeeze methodology, the cement slurry is circulated down through the bottom perforations up to the top perforations, the packer placed in between, with returns back into the wellbore. There is a strong possibility that, if the cement volume is larger than the volume of the channel or void intended to be covered, some of the cement slurry may enter the casing / work-string annulus (behind the packer tool) during the job. Should this cement set, the DP or tubing may become stuck in the hole. This is an immediate and unwanted possibility only worsened by the amount of cement slurry above the packer setting depth and the proximity of the packer to the top perforations.
Coming back a little, let’s recognize the root of the problem: “cement volume is larger than the volume of the channel or void intended to be covered”. This problem is not because we can’t do our math; this is a problem since we don’t really know the geometry of the channel, particularly if old/damaged/fractured cement is in placed (original primary cement job), and because circumferential flow is not ensured (cement will flow only through the easiest path). But, there is another contributing element, the minimum-pumpable cement volume. This is the minimum cement volume we should pump to ensure “uncontaminated” cement slurry fills the channel or void (the cement slurry would normally undergo mixing and contamination with the fluids ahead while flowing down the workstring – the deeper the packer the higher the contamination). In summary, in a circulating squeeze operation of this nature it is likely to highly-likely that cement slurry (in addition to cement-contaminated fluids) would return back to the wellbore behind or on top of the packer. What are the implications?
- Cement slurry can impair the mechanism to unset the packer;
- The cement slurry back into the wellbore could have unpredictable behaviour (thickening time reduced and increased gel strength) due to its interaction with a permeable media (filtration) while flowing behind the casing from the bottom perforations;
- The workstring (DP or tubing) may accidentally become stuck in the hole.
As a summary, let’s put all in perspective; in suicide squeeze cement slurry in an unknown quantity with unknown thickening time might end up in the active wellbore in contact with the workstring and behind the packer; a relative large OD tool (with respect to the casing ID). In other words, a game of chance that makes the term “suicide squeeze” even more clear now.
Now, let me go further back to our second question, why do it?
I bet you anticipated a large answer to this one. But, you already now the answer, correct? A suicide squeeze is considered and executed because there is no other choice! Right? So, for all purposes I assume that if a suicide squeeze job is considered is because all other options were explored and discarded as inapplicable.
What can be done to increase our chances?
First of all, we must perform a team-wide operational and technical job risk assessment to recognize all risks and identify proper preventive or remedial measures. Below some applicable actions:
- Consider using a cement retainer for a simpler process. Easier and quicker to remove the stinger assembly than the packer, and POOH with a wider effective workstring-casing gap.
- Make sure the interval is circulated to ensure best possible cleanup and a steady circulating pressure. Fluids like acid, water or a wash can be considered, before cementing, keeping in mind density and chemical compatibility.
- Evaluate and take action on possible fluids incompatibilities (cement / brine or mud / spacer or wash). Some cement-contaminated fluids behaviors include: reduced thickening time, increased and/or shortened static gel strength, solids settling and delayed compressive strength development, among others.
- The cement slurry should be:
- Low viscosity with very low gel strength for easier flow (less pressure drop in the channel = less filtration);
- Zero free water; and
- Less than 50 ml/30 min fluid loss.
- An additional safety factor shall be considered for thickening time. In these operations the actual thickening time might be reduced and gel strength development considerably accelerated due to the loss of filtrate while the cement slurry flows under pressure behind the casing between the perforations.
- Cement slurry volume estimation shall be as conservative as possible. Use the fluids contamination feature of the cement placement simulation software to predict / estimate the minimum-effective pumpable volume.
Finally, I would like to emphasize that performing a “suicide squeeze” has to be a team’s decision. Every member of the team should be involved from start, understanding the risk and implications. A drilling engineer or the cementing specialist, if available, should prepare an initial presentation describing the process, assumptions, risk management, pros and cons. In a way, like sorts of “suicide squeeze on paper or SSOP” exercise so, everybody can contribute and be part of the process.
Please drop your questions or comments in the space below. I will be glad to answers your questions, or receive your contribution to enrich this article.