The Challenge
Production was declining at a mature oil field where the Bashkirian stage is represented by highly heterogeneous carbonate reservoirs. Severe layering, vertical fracturing, and thin impermeable barriers had caused the existing waterflood to sweep only the most permeable intervals. As a result:
- The effectively swept pay thickness was typically below 50% of the perforated interval;
- Water cut had reached 73–94% and kept rising;
- The recovery factor seriously lagged behind the target of 0.38;
- Previously trialed methods – small-volume crosslinked polymer gels and cyclic waterflooding – failed to redistribute flow deep within the formation.
The operator needed a solution that could unlock the remaining oil in low-permeability streaks without drilling new wells and without heavy capital expenditure.
The Solution
In 2005, Idzhat launched a pilot project on 28 injection wells using Polymer-Disperse Systems (PDS). The system is designed to selectively increase flow resistance in high-permeability watered-out zones. Because PDS is injected in large volumes, the agent travels far beyond the near-wellbore area. This forces the injected water to divert into oil-saturated intervals that had previously been bypassed, improving vertical sweep efficiency throughout the reservoir.
Evaluation Methodology
Performance was assessed as of September 2007 – more than two years after the first treatments. To ensure the results reflect only the PDS effect, several rigorous steps were taken:
- Production logging (PLT) surveys before and after injection confirmed that injection profiles had changed and new intervals had been activated.
- All production wells that underwent well interventions (acid jobs, water shut-off, pump upsizing, etc.) in the baseline period or after the PDS treatment were excluded from the calculation. Cyclically operated wells were also disregarded.
- Where pump sizes or operating modes changed, corrections were applied to eliminate overlapping effects.
- Incremental oil and produced water reduction were quantified using displacement characteristic methods (Sazonov, Nazarov-Sipachev, Kambarov), which are widely accepted in the industry for waterflood evaluation.
Key Results
(all volumetric figures are in barrels)
| Metric | Value |
|---|---|
| Injection wells treated | 28 |
| Total incremental oil recovery | ≈ 376,100 bbl |
| Reduction in produced water | ≈ 15,470,000 bbl |
| Incremental oil per well treatment | ≈ 14,460 bbl |
| Average effect duration | 17 months (still ongoing in 9 well patterns at the cut-off date) |
| Average daily oil gain per pattern | ≈ 27.9 bbl/d |
Conversion factors: 1 metric ton of oil ≈ 7.33 bbl; 1 m³ of water ≈ 6.2898 bbl.
The PLT data delivered striking visual proof: in the treated injection wells, the intake profile became significantly more uniform. Some previously dominant intervals took less water, while earlier inactive or poorly swept streaks started to accept injection and push oil towards the producers. On individual patterns, water cut dropped by 3–5 percentage points, oil rates increased, and the volume of lifted water fell. Notably, later acid stimulations performed on some injection wells did not produce any additional incremental oil, underlining that the PDS effect was deep and robust.
Conclusion & Next Steps
The pilot demonstrated that PDS technology is highly effective in the challenging environment of heterogeneous carbonate waterfloods:
- Without any new drilling, the operator gained approx. 376,000 barrels of incremental oil and avoided over 15.5 million barrels of produced water, lowering lifting and water-handling costs.
- The results were approved by the operator’s technical management and the technology was recommended for full-field rollout across other assets with similar reservoir characteristics.
The project shows that even at a very high water cut, a well-designed diversion treatment can access substantial remaining reserves – turning a depleted pattern into a profitable one.
Based on the 2008 analysis report of pilot PDS operations performed in 2005–2007.