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Perforations in the wrong place 
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Joined: Tue Aug 16, 2011 9:42 pm
Posts: 13
Post Perforations in the wrong place
I am sure that many of us have experienced seeing well logs that indicated the well would be a good producer just to see it tested as a poor well, or even P&A'd as a dry hole. This has happened, expecially in deep wells with thin pay zones. I may have found a possible explanation. The World Oil ran an article in the January Issue, 2008. A copy of that paper is attached.

After reading that paper, as best as I have been able to determine, NONE of the perforating companies are taking gun movement after the winch is stopped in account when positioning the gun to fire. I would appreciate your thoughts on this problem, and expecially what we can do to prevent good wells performing poorly, or being P&A'd.


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Wed Aug 17, 2011 1:33 am

Joined: Tue Mar 15, 2011 3:13 pm
Posts: 20
Post Re: Perforations in the wrong place
It was interesting to read a paper on Creep. I am working as logging engineer since last 5 years. I have worked with two major companies but none of them taught me about creep.
If my understanding is not wrong then the author of paper has suggested three solutions to avoid creep problem. But I am not sure how can service company implement them

1) Compare downlog to uplog of CCL near perforation zone at normal logging speed. If there is a difference then it means that wireline is stretching during uplog and, consequently, the creep occurs when winch is stopped for perforation. But this just an indication of creep happening. It doesn't tell how much creep will occur.

2) "Another simple way to determine whether creep might be a problem is to stop the winch abruptly and see if the casing collar locator continues to “rattle” for a half a second or more." Whatever CCL I have run there is no way to know if CCL is rattling. Even if CCL is stationary, it keeps on giving basic noise. Again, this just an indication of creep happening. It doesn't tell how much creep will occur.

3) "to perforate while moving". It is very dangerous and split delay of a second can cause engineer shooting way off depth.

I suggest someone should do a study to determine how much creep occurs in how much time. let say, the perforation is done immediately after winch is stopped, in that case the creep might be negligible.
Another suggestion would be to go down atleast 3 collars below perforation zone and record up CCL as slowly as possible to minimize stretch and this will minimize creep in result when winch is stopped. But I find very difficult to get CCL below 20-25 ft/min logging speed even if gain and threshold are properly adjusted
The only solution that I think with my little knowledge is to use GR for correlation as GR can be recorded as slow as possible. The less logging speed will cause less stretch in wireline for a given well and, consequently, less creep when wireline stopped for perforation.


Wed Aug 17, 2011 11:07 am

Joined: Tue Aug 16, 2011 9:42 pm
Posts: 13
Post Re: Perforations in the wrong place
You are correct, his paper does not give enough information to be able to determine creep. I have found that the up log compared to the down log only indicates that creep is a problem. It does not reveal how much the creep is, but only that it need to be determined and adjusted for. I have found that perforating on the run almost assures that the perforations are not correctly placed.


Wed Aug 17, 2011 3:22 pm

Joined: Tue Mar 15, 2011 3:13 pm
Posts: 20
Post Re: Perforations in the wrong place
There is a paper published by Schlumberger on Creep in wireline logging. If you have copy of that please let me know. I tried to download it from internet but it is not free.


Thu Aug 18, 2011 4:39 am

Joined: Tue Aug 16, 2011 9:42 pm
Posts: 13
Post Re: Perforations in the wrong place
I do not have a copy of that paper. I do know that Peter Fitzgerald authored a paper that was presented in the middle East, I think. It is obvious that Peter does believe that creep is a major issue. However, as the Pledger paper pointed out, there is a great amount of field evidence that many perforations are not where they were planned. If creep is neglected, the perfs will be higher than planned. How many times have oil zones been found with a gas/oil contact, and when the well was perforated, the production came in high GOR. Most of us have assumed that gas was being coned into the perfs. However, could it be that the gas was perforated because creep was neglected?


Thu Aug 18, 2011 5:22 pm

Joined: Tue Mar 15, 2011 3:13 pm
Posts: 20
Post Re: Perforations in the wrong place
I think it should be possible to calculate approximately how much is the creep when winch is stopped. There will be two type of stretch in wireline when winch is moving upward. One is due to weight of cable and tools and another one due to drag exerted on wireline and tool by surrounding mud. When winch is stopped there will be no more drag, and that time there will only be stretch due to weight.
The drag eqn is
F = 1/2 (Rho) (V^2)(Cd)(A)

F = Net Drag Force
Rho = Density of surrounding Fluid
V = Velocity of moving object
Cd= Drag Coefficient
A = Surface Area

I think if someone can determine drag coefficient chart experimentally for different guns wrt different casing sizes then we can accurately determine F, and from which we can calculate stretch, which is theoretical CREEP.


Sun Aug 21, 2011 5:07 pm

Joined: Tue Aug 16, 2011 9:42 pm
Posts: 13
Post Re: Perforations in the wrong place
I also believe that it can calculated. However, there are many factors that must be known for this calculation. The speed at which the tools are being moved is one of the greatest factors. The OD of the tools compared to the ID of the casing. The viscosity of the fluid in the hole, the weight of the tools. The well deviation profile must be accurately known. The size of the wireline. All of these factors impact creep, and there may be others that I have not identified. I have been in the industry for 51 years, and have thus far, not been able to calculate creep. I have seen a good straight hole at 7,200' have only 2 feet of creep, when the adjacent well, with two dog-legs, had 9' of creep at the same depth.

Because creep is a reality, and highly impacts the quality of our completions, it should be determined and compensated for every time we perforate. One thing I do every time I study a problem well is ask the question, "what would this well act like if the perforations were 5' or 10' or 20' higher than we think they are." The most creep I have seen was 30' at 16,500' in an Oklahoma well. As fields age, and wells are being recompleted into new pay zones,MANY OF WHICH ARE THIN ZONES, creep determination becomes critical to recover all the reserves the well has penetrated.


Sun Aug 21, 2011 7:34 pm

Joined: Tue Mar 15, 2011 3:13 pm
Posts: 20
Post Re: Perforations in the wrong place
I am surprised why Baker and Halliburton are not correcting for it. I am not sure about Schlumbeger.


Sun Aug 21, 2011 7:42 pm

Joined: Tue Aug 16, 2011 9:42 pm
Posts: 13
Post Re: Perforations in the wrong place
In January, 2009, Schlumberger (Peter Fitzgerald) was granted a patent on creep. If you Google "creep Patent" it should be on the first page. As best I can tell, Schlumberger has made no changes in their field operations. I have talked with many other perforating companies, and NONE of them find or adjust for creep. Many of them do not know what creep is, let alone, how to find it and compensate for it. Most of them will tell you that creep is not a problem and does not need to be determined. Ask them for yourself and see if this is the truth.


Sun Aug 21, 2011 8:29 pm

Joined: Wed Sep 01, 2010 10:06 pm
Posts: 107
Post Re: Perforations in the wrong place
Nice discussion here!
I am absolutely not in this field, but couldn't this be solved by lodging the tool in the hole with arms, letting the line slack a little and then pulling back until tension (which could also be measured downhole, right?) reaches a certain value. Couldn't downhole tension and tension measured on the rig be used to deduct the amount of creep?

I may be way off here though....


Mon Aug 22, 2011 7:20 pm
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