Understanding a subsurface pipe failure

[hogwildwa]

TL;DR Summary

During a fracturing operation, fluid leaves the pipe through a perforated cemented sliding sleeve. We have noticed that the pipe is being deformed a few feet on either side of the sleeve. I am trying to figure out what is causing the deformation.

The situation is that we have 4.5 inch diameter pipe with a 300,000 lbf yield rating installed in a horizontal completion. The pipe is cemented in place but it is very likely that the one side of the pipe may not have any cement in it. During the fracturing operation, a sleeve is opened and fluid is pumped out the casing at a pressure of 5300 psi. The reservoir pressure that would help support the cemented portion of the pipe is 1700 psi. We have noticed that the pipe deforms on either side of point where the fluid exits the casing. I believe that the incomplete cement support is allowing high pressure on one side of the pipe which is producing a force/bending moment that is deforming the pipe. I tried some simple calculations but I am not sure that I am looking at the problem correctly. Attached is my evaluation. I would appreciate any comments.

 

[Ranger Mike]

I have been working in this area for a year. A manufacturing company making pipe elbows for the fracking industry had a problem with blow by of the elbow to pipe connection at 15,000 psi. My first question is “ How out of round are the coupling surfaces”.

Castings are machined to tolerance but the control of SIZE is only one indication of functionality. So how does form error or Out of Roundness (ovality, roundness etc..) effect the pipe? The best way to handle stress in all directions is the circle. This is why raindrops are round when they puddle on the sidewalk. The circle resists force ( atmosphere of 14 psi at sea level) equilaterally. If we take this one more step, if the pipe is really out of round then the pipe can not handle force equilaterally. This form error can not be measured with calipers micrometers or V-blocks.

 

[hogwildwa]

This is large scale oilfield pipe, similar to what you might use for surface pipelines. The normal burst pressure is about 8000 psi. It is not perfectly round but it is pretty round. General we are running a few thousand feet of it and would not caliper it. I am really trying to understand whether high pressure on one side of the pipe in a void in the cement could provide sufficient force to deform the pipe.

 

[JBA]

Your description and illustrations are a bit confusing to me as to the "pipe" vs. the "casing". In my past experience with fracking (although on vertical well completions) the casing is cemented to the formation and then perforated and subsequently the fracking pressure is applied to the interior of the casing and to the formation. In that scenario, the unsupported section (which you show as being in the region of the perforated section of the casing) would be pressure balanced as the the fracking pressure is applied.

 

[hogwildwa]

thank you for your response. You're absolutely right in the scenario that you mentioned the vertical well with good cementing and perforating, the pressures would be balanced. In this case we're talking about a horizontal well where cementing is problematic and it's very likely that there is a void in the cement on the top of the pipe. We have noticed this in a number of cement evaluation logs. In addition access to the formation is not to perforations but it's through a shifted sleeve. And that scenario the side of the pipe that has good cement would not see the pressure until the cement failed. The other side of the pipe with little or no cement would have the pressure build up in that area. That's the scenario that I'm trying to describe here. Basically, I'm trying to understand why we are seeing pipe deformation on each side of these sleeves after every frag job. this has caused us to have tools get stuck a number of times. I hope this is a little bit clearer.

 

[hogwildwa]

JBA,

Here is a link to the SPE website and a paper on cemented sleeves.

https://www.onepetro.org/journal-pa...een=&fromSearchResults=true&to_year=&rows=25#

 

[JBA]

Thanks for the reference, using its title as a reference led me to the below Halliburton video for "Multistage Continuous Pressure Fracturing".

https://www.halliburton.com/en-US/p...etions/horizontal-completions/rapidstage.html

As a result, I think I now have a better understanding how the sleeve method is employed; but, with the sleeve withdrawn and the perforations open, the void region can only be pressurized to the fracking pressure by the applied fracking pressure inside the casing so it would still appear that until the internal fracking pressure in the casing is vented there is still a pressure balance between the inside and outside of the casing in the void region.
As a result, my primary focus is still on the mechanics of how an eccentric pressure or loading might be applied to deform the casing; and, leaves me with questions and comments none of which contradicts your current assumption that a cementing void is a factor in the problem.
(Note: I admit I am still unclear on the formation fracturing mechanics for horizontal completions in that for vertical completions the accepted concept for the pressure required to fracture an oil sand, where the fractures are horizontal, is the pressure required to overcome and lift the overburden load on the formation, which is clearly not applicable for vertical fractures with horizontal displacements from horizontal completions.)
1. Is your fracking a continuous pressure ball activated closing method similar to that shown in the referenced video?
2. You first state the pipe "is being deformed a few feet on either side of the sleeve" and then you next describe it being "on either side of point where the fluid exits the casing". Please clarify these apparently conflicting statements.
3. You state that the deformation is an issue for running tools through the casing and if it is taking place during the fracking process it would seem that the problem would first be observed by interfering with the closing of the sleeve or its reopening after the completion of the fracking process.
4. One speculation thought that comes to my mind, assuming you are using proppants and the cement void is in the region of the casing ports, it would seem that during the injection process the proppants would migrate into and fill that void at high pressure and, if the continuous pressure method is used, then the sleeve is closed; and, I wonder whether or not that would somehow how be a contributing factor to the problem.

 

[hogwildwa]

Thanks for the reference, using its title as a reference led me to the below Halliburton video for "Multistage Continuous Pressure Fracturing".

https://www.halliburton.com/en-US/p...etions/horizontal-completions/rapidstage.html

As a result, I think I now have a better understanding how the sleeve method is employed; but, with the sleeve withdrawn and the perforations open, the void region can only be pressurized to the fracking pressure by the applied fracking pressure inside the casing so it would still appear that until the internal fracking pressure in the casing is vented there is still a pressure balance between the inside and outside of the casing in the void region.
As a result, my primary focus is still on the mechanics of how an eccentric pressure or loading might be applied to deform the casing; and, leaves me with questions and comments none of which contradicts your current assumption that a cementing void is a factor in the problem.
(Note: I admit I am still unclear on the formation fracturing mechanics for horizontal completions in that for vertical completions the accepted concept for the pressure required to fracture an oil sand, where the fractures are horizontal, is the pressure required to overcome and lift the overburden load on the formation, which is clearly not applicable for vertical fractures with horizontal displacements from horizontal completions.)
1. Is your fracking a continuous pressure ball activated closing method similar to that shown in the referenced video?
2. You first state the pipe "is being deformed a few feet on either side of the sleeve" and then you next describe it being "on either side of point where the fluid exits the casing". Please clarify these apparently conflicting statements.
3. You state that the deformation is an issue for running tools through the casing and if it is taking place during the fracking process it would seem that the problem would first be observed by interfering with the closing of the sleeve or its reopening after the completion of the fracking process.
4. One speculation thought that comes to my mind, assuming you are using proppants and the cement void is in the region of the casing ports, it would seem that during the injection process the proppants would migrate into and fill that void at high pressure and, if the continuous pressure method is used, then the sleeve is closed; and, I wonder whether or not that would somehow how be a contributing factor to the problem.

WRT to 1 and 3. The sleeves are open with a shifting tool conveyed by coiled tubing. The tubing and shifting tool stay in the hole during the fracturing operation. The OD of shifting tool is close to the casing ID dimensions so when deformation occurs, the shifting tool can become stuck.

WRT to 2, There is no conflict here as the fluid exits the casing through the sleeve and the deformation is occurring on either side of the sleeve (in most cases).

Deformation has been observed even when proppant wasn't pumped. Also, these wells used a crosslinked hydroxypropyl guar frac fluid with a viscosity in the 100's of cP the proppant should normally be transported efficiently past the void section.

 

[hogwildwa]

Thanks for the reference, using its title as a reference led me to the below Halliburton video for "Multistage Continuous Pressure Fracturing".

https://www.halliburton.com/en-US/p...etions/horizontal-completions/rapidstage.html

As a result, I think I now have a better understanding how the sleeve method is employed; but, with the sleeve withdrawn and the perforations open, the void region can only be pressurized to the fracking pressure by the applied fracking pressure inside the casing so it would still appear that until the internal fracking pressure in the casing is vented there is still a pressure balance between the inside and outside of the casing in the void region.
As a result, my primary focus is still on the mechanics of how an eccentric pressure or loading might be applied to deform the casing; and, leaves me with questions and comments none of which contradicts your current assumption that a cementing void is a factor in the problem.
(Note: I admit I am still unclear on the formation fracturing mechanics for horizontal completions in that for vertical completions the accepted concept for the pressure required to fracture an oil sand, where the fractures are horizontal, is the pressure required to overcome and lift the overburden load on the formation, which is clearly not applicable for vertical fractures with horizontal displacements from horizontal completions.)
1. Is your fracking a continuous pressure ball activated closing method similar to that shown in the referenced video?
2. You first state the pipe "is being deformed a few feet on either side of the sleeve" and then you next describe it being "on either side of point where the fluid exits the casing". Please clarify these apparently conflicting statements.
3. You state that the deformation is an issue for running tools through the casing and if it is taking place during the fracking process it would seem that the problem would first be observed by interfering with the closing of the sleeve or its reopening after the completion of the fracking process.
4. One speculation thought that comes to my mind, assuming you are using proppants and the cement void is in the region of the casing ports, it would seem that during the injection process the proppants would migrate into and fill that void at high pressure and, if the continuous pressure method is used, then the sleeve is closed; and, I wonder whether or not that would somehow how be a contributing factor to the problem.

WRT to 1 and 3. The sleeves are open with a shifting tool conveyed by coiled tubing. The tubing and shifting tool stay in the hole during the fracturing operation. The OD of shifting tool is close to the casing ID dimensions so when deformation occurs, the shifting tool can become stuck.

WRT to 2, There is no conflict here as the fluid exits the casing through the sleeve and the deformation is occurring on either side of the sleeve (in most cases).

Deformation has been observed even when proppant wasn't pumped. Also, these wells used a crosslinked hydroxypropyl guar frac fluid with a viscosity in the 100's of cP the proppant should normally be transported efficiently past the void section.

 

[JBA]

Please understand what I am trying to accomplish here is to consider as many possible alternative scenarios that might be factors in what is occurring.

While as a new product development engineer for high pressure relief valves I attended a seminar on "creative design" by an engineering dean; and, in that seminar he stated that "you have not investigated all possible solutions until you have ten candidates, no matter how improbable some may be" while ten isn't a magic number, the point being that this opens your mind and prevents initially starting to focus on a single first idea; and, I found this philosophy to be of value.

I have a couple of additional questions:
1. To be sure I understand completely, by your statement that the deformation occurs at either "side" of the sleeve I assume you mean at either "end" of the sleeve?
2. How far is each end of the sleeve extend from the casing ports location and are there multiple ports located circumferentially around the casing at the port location?
3. Does the cement void extend beyond the end(s) of the sleeve?

In this respect I am considering whether or not the sudden pressure drop in the void when the formation fractures could be be creating a pressure differential spike between the casing ID and OD deforming the unsupported casing into the void and; as a result, ovaling the casing on the sides adjacent to void.

Also, I wonder what effect, if any, there is due to the fact that in the cemented regions of the ports the pressure must fracture the surrounding cement as well as the adjacent formation; whereas, with the old perforate and frack procedure there was initial cement perforation and localized formation fracturing at the port location(s) from the explosive perforating prior to applying the fracking pressure.

 

[256bits]

Your description and illustrations are a bit confusing ...".

Same here, but that's just me, I've worked in mining but not the oil.
@hogwildwa
Interesting topic due to the progression of technology in this industry.

In the Word attachment, the word "void" is used.
I have trouble imagining what the term would mean. Void of cement certainly fits the description, but it does seem troublesome that the "void" would only be at the locations of stimulation along the line.
Improper cementing - mentioned in post 5 cementing logs - just by random occurrence to have voids at the stimulation location, would indicate quite a few ( many) voids along the line.

Would an unstable formation have anything itself to do with pipe deformation?
Any history for that as being a cause of pipe deformation in the industry.

 

[JBA]

During my time in the production and well servicing industry was restricted to oil bearing sandstone formations that tended to be uniform in structure and fractured horizontally; so shale structure fracture and dislocation mechanics due to pressure fracturing are a mystery to me.

A quick review of some paper abstracts related to shale formations indicates that an array of natural horizontal fractures are present in shale formations. The below is an example:
https://repositories.lib.utexas.edu/handle/2152/47320

That information, leads me to consider whether or not vertical expansion of existing horizontal fractures near the casing during fracking might be able to deform an unreinforced section of casing.