Abstract
This case study illustrates a methodology adopted by an operator to reveal the dominating mechanism behind dramatic watering-out sequence, prevailing production from a mature gas condensate field in Eastern Europe. A production restoration project was triggered to understand and remedy the adverse effect of water. Finally, its source could be solely verified with the help of numerical simulation.
Many attempts to isolate or handle excessive water production fail, because remediation activities are deployed in the trial- and-error manner, without prior water source identification. Possible reasons that operators simplify their approach by reverting to the best practices/analogs, not accounting for individuality of the problem. Furthermore, ineffective water shutoff jobs are not always analyzed for their pitfalls and consequently fed to the next well. Thereby, the process lacks true insight of the nature of water appearance and, in turn, the right remediation strategy from start, if it exists.
The field development showed that, after water breakthrough, the gas rate dropped by a factor of 4 or 5, thus leading to huge production losses. First, water production occurred in the crest of the structure followed by a sequence of wells being watered-out. The past experience to isolate the invading zone accompanied with extensive logging and misleading choking-back, revealed the necessity of thorough water diagnostics. The well-known categories of problems were analyzed tying them to subsurface uncertainties and vast reservoir information. Simple types were gradually replaced by complex processes, or even by the combination of the following: faulting, multilayered channeling, system of fractures etc. The formed concepts were reviewed in the simulation model honoring available buildup/per-interval pressures, casedhole production/saturation logs and repeated openhole logs to obtain the historical water/gas ratio (WGR) evolution. Finally, the strategy was refined giving ideas for deepening of the wells and downdip sidetracking in the less invaded zones.
