Build up pressure appear after sharp decline.......Please help

[bayan]

There is reservoir three phases, oil,gas and water,it was sharp pressure decline during about 4 years after that build up pressure appear suddenly in the reservoir.any Eng. have explaining that phenomena.the reservoir has stronge aquifer
Thank you in advance for any comments

[vinomarky]

Ruling out measurement errors, reduction in offtake and other such basic avenues, a front runner may be pressure sensitive/active faults

[bayan]

Thank you so much for the explanation. I inquire how active faults effect build up pressure? could you please explain that?
Thank you

[kochichiro]

Look at your production history, you are probably having variable withdrawal rate.
For example, at the beginning of production oil rates were significantly higher and each year they dropping drastically. Thus, inflow from aquifer compensated and later overcompensated pressure decline from production. It is the case, when you are having low-permeability aquifer or bottom aquifer.

In my experience, I encountered tight oil field with aquifer, during first 5 years of production initial reservoir pressure declined from 300 atmospheres to 150 atmospheres. After that field was abandoned for 10 years, but there was small unofficial oil production from it (approximately 10 barrels a week). After 10 years when field started to be re-vitalized by another company, they discovered that reservoir pressure returned to its initial value – 300 atmospheres.

[vinomarky]

If there was a sealing fault (ie clay smear) separating your oil reservoir from other oil compartments (or indeed an aquifer), which under a certain delta P broke down, allowing some degree of communication, then you may see an apparent increase in pressure. Kockichiro's suggestion is also a valid alternative to consider in lower perm reservoirs.

[bayan]

Thank you every one and I'm appreciated any help.
Best Regards