Executive Summary
This case study examines the application of a tailored Polymer Dispersed System (PDS) in a mature oil field characterized by extreme vertical heterogeneity and high formation water salinity (up to 272 g/L). After decades of conventional waterflooding, a high-permeability sandstone layer (Zone A4) was acting as a thief zone, resulting in inefficient sweep of the main oil-bearing layer (Zone A3) and an average water cut exceeding 94%.
A modified PDS formulation, optimized for high-salinity brine, was injected into three key injection wells. The treatment successfully blocked the dominant flow channel in Zone A4 and diverted injection pressure into the previously unswept Zone A3. Over a 16-month evaluation period, the operation delivered ~47,100 bbl of incremental oil and reduced produced water handling by ~1.26 million bbl.
The Challenge: High Water Cut and Bypassed Oil
The target reservoir interval comprises alternating sandstones, siltstones, and shales across multiple zones.
- Geological Complexity: Zone A4 exhibits high permeability (up to 5,300 mD) but limited thickness, while Zone A3 contains the bulk of remaining reserves with moderate permeability (250–3,200 mD).
- Pre-Treatment Status: Injected water was cycling rapidly through Zone A4. Offset production wells were operating at marginal economic rates with water cuts as high as 97.5%. Average daily oil production from the pilot area was 73 tonnes/day (~535 bbl/d).
The Solution: Tailored PDS Formulation for High Salinity
Laboratory studies were conducted to adapt the chemistry to the field’s specific brine (272 g/L TDS).
- Formulation Optimization: Testing of various polyacrylamides and cross-linkers confirmed that robust gelation is achievable even at high salinity. The optimal formulation utilized a PDS modified with Aluminum Chloride, achieving a high Residual Resistance Factor (Rres = 3.94) in the thief zone.
- Mechanism: The PDS system effectively reduces the hydraulic conductivity of the high-permeability streaks, forcing subsequent injection water to pressurize and sweep the tighter, oil-saturated adjacent layers.
Field Implementation
A total treatment volume of ~16,300 bbl (2,591 m³) was injected across Wells 50, 64, and 67. The treatment consisted of sequenced slugs of aluminum chloride, polymer solution, and dispersed particle suspension.
| Well ID | Treatment Volume (bbl) | Pre-Treat Injectivity (bbl/d) | Post-Treat Injectivity (bbl/d) | Primary Outcome |
|---|---|---|---|---|
| Injector 50 | ~5,260 | ~2,010 @ 105 bar | ~1,130 @ 150 bar | Reduced flow capacity in Zone A4; activation of Zone A3 |
| Injector 64 | ~3,670 | ~1,810 @ 140 bar | ~1,320 @ 150 bar | Flow redistribution within Zone A3 |
| Injector 67 | ~7,370 | ~1,130 @ 120 bar | ~1,320 @ 140 bar | Pressure build-up and diversion into unswept Zone A3 |
Validation:
Pressure fall-off tests and injection profiling confirmed a 40–67% reduction in hydraulic conductivity within Zone A4. This validated that the treatment achieved deep conformance control rather than just near-wellbore skin damage.
Operational Results
The pilot area included 22 offset production wells. A positive production response was observed in 55% of the well stock.
- Immediate Oil Response: Within three months, average daily oil production across the pilot area increased by 22%, peaking at an additional 16 tonnes/day (~117 bbl/d).
- Water Cut Reduction: Significant reductions in water cut were observed in key producers:
- Well 55: Water cut decreased from 68.3% to 52%. Oil production increased from 4.9 tonnes/day (~36 bbl/d) to 9.3 tonnes/day (~68 bbl/d).
- Well 54: Water cut decreased from 97.5% to 94.2%. Oil production increased from 0.6 tonnes/day (~4.4 bbl/d) to 2.2 tonnes/day (~16 bbl/d).
- Well 34: Water cut decreased from 96.5% to 92.6%. Oil production increased from 2.6 tonnes/day (~19 bbl/d) to a peak of 5.8 tonnes/day (~43 bbl/d).
Sustained Recovery (16-Month Period):
- Incremental Oil: 6,430 tonnes (~47,100 bbl)
- Reduction in Produced Water: 201,000 tonnes (~1.26 million bbl)
Conclusion
This pilot project demonstrates the technical and operational viability of modified Polymer Dispersed Systems in high-salinity, mature sandstone reservoirs. By successfully diverting flow from a high-permeability thief zone into an oil-rich, lower-permeability layer, the operator achieved a material uplift in oil recovery while substantially reducing water handling volumes. The results support the expansion of this technology as a proven strategy for improving sweep efficiency in analogous heterogeneous reservoirs worldwide.