Answer:
PDS is not inherently “better” in one lithology. It is a purpose‑engineered conformance technology whose performance is shaped by the reservoir’s void‑space architecture. Its decisive advantage is the ability to tune the size of the isolating floccules to match the specific flow‑path dimensions – pores in sandstones, fractures in carbonates. The true measure is not superiority, but adaptability and value creation in both environments.
1. What fundamentally differs between sandstones and carbonates?
- Sandstones are dominated by a pore‑throat network with layered permeability contrasts. The primary flooding problem is early water breakthrough through high‑permeability streaks, leaving lower‑permeability lenses unswept.
- Carbonates present a dual‑ or triple‑porosity system (matrix, fractures, vugs). Permeability contrasts are extreme; injected water channels almost instantly through open fractures, completely bypassing the oil‑filled matrix.
2. How PDS adapts: floc size tuned to pore or fracture scale
The technology relies on sequential injection of a low‑viscosity polymer solution and a dispersed particulate suspension. In the reservoir, these components undergo in‑situ coagulation and flocculation, forming aggregates with a deliberately engineered size distribution.
- In sandstones the floccules are designed to reach pore‑channel size, plugging high‑perm streaks and diverting water into bypassed matrix zones.
- In carbonates the floc size is expanded to bridge and seal open fractures, shutting off thief conduits while preserving oil flow from the matrix.
This unique tunability – from pore‑scale to fracture‑scale – makes PDS a lithology‑agnostic conformance platform, effective wherever high‑contrast flow pathways exist.
3. Laboratory and field evidence
Laboratory validation:
- Video microscopy confirms that post‑flocculation aggregates are significantly larger than individual pore throats, ensuring selective plugging.
- Residual resistance factor (RRF) tests show that conventional polymer solutions lose effectiveness as permeability increases, while PDS gains resistance – a direct proof that it targets the highest‑conductivity channels.
- In carbonate corefloods, PDS raised oil displacement from near‑zero to 6.5‑13.9 percentage points in low‑permeability layers.
Field‑performance summary:
| Lithology | Deployment scale | Total incremental oil | Average per treatment | Key operational impact |
|---|---|---|---|---|
| Sandstones (Volga‑Ural, West Siberia) | ~2,000 well treatments | ~41.6 million bbl | ~21,200 bbl per operation | Deep diversion in layered reservoirs; established, large‑volume economic uplift |
| Carbonates (Volga‑Ural region) | 87 pilot areas | ~1.21 million bbl | ~13,900 bbl per operation | Fracture shut‑off and matrix sweep restoration; transforms watered‑out wells into commercially viable producers |
Bottom line
PDS doesn’t ask operators to choose between sandstones and carbonates. The same fundamental chemistry is engineered for each reservoir’s flow‑path geometry. Sandstones yield higher absolute per‑treatment volumes; carbonates deliver a greater relative production recovery from technically stranded matrix oil. The technology’s unique competitive edge is its ability to set the size of the isolation barrier exactly to the target – pores or fractures – making it a genuinely universal solution for mature waterflooded assets.