Workover in heavy oils, well performance reduction

[dev_r]

Hi everyone,

On some Canadian fields (heavy oil) it was observed that well performance decreased after workovers, whereas one would expect reverse results.
Any expatiations why?
Can anyone advise reading material or field experience on heavy/ highly viscous oil workovers?

Thanks for help.

[Land_Mark]

Many possible reasons,

Including;

1. Heavy oils with asphaltene content - certain workover fluids with certain ionic salts of metals may cause asphaltenes to become unstable and drop out of the stream and become deposited.
2. Alteration of relative permeability of oil due to excessive completion fluid leakage into formation, thereby increasing the saturation of water in the near wellbore region and decreasing the rel. perm to oil.
3. Excessive near wellbore cooling or that the workover fluid was hot water which entered the formation but was allowed to cool, causing a zone of wax precipitation in the near wellbore region.
4. Any other problems related to deposition of impurities in heavy crude oil.
5. Possibly need to refine workover strategy to properly cleanout the wellbore and wash perforations from time to time.

Markus L.

[dev_r]

Hi Markus,

Great response, thanks. I am dealing with horizontal well in an unconsolidated reservoir and I assumed that lower well performance caused by the fact that if there was circulation of fluid and when all these sediments/particles settled that lead to blocking of near well bore region.
Besides, these particles tend to block high permeable zones.
Is this possible?

Could you please advise me reading material or literature where I can find this? Any SPE or other tech articles.

Thanks.

Regards,

Dev

[Land_Mark]

Dev_r,

Try to verify where the restriction exists; if it does in the near wellbore region, then pressure transient testing will help and if you do have results from previous transient tests, you can track the evolution of the near wellbore restriction with time, so if the skin has increased over time you can make some assumptions (as those I stated before) then try to eliminate by going through the crude characterization reports (asphaltene content, wax content, fines content) and workover history (fluid leakage into formation, hot water circulation) to pinpoint the main causative factors or combinations of them. When you've found your problem, you can use resources like "Production Operations Vol. 1 and 2" or other books that suggest solutions to problems like these.

Markus L.