Rock-Fluid Interactions in a Tight Sandstone Reservoir
Bibliographic record
Abstract
Abstract In this work, we present a comprehensive and practical framework to quantify the dynamic characteristics of pore-throat structure together with wettability alterations during a waterflooding process in a tight sandstone reservoir in addition to evaluating the impact of ionic composition and salinity on its performance. Thin section analysis, XRD analysis, SEM tests, PMI and RMI experiments, contact angle measurements, zeta potential tests, and displacement experiments with and without surfactants are integrated. In a reservoir, throats with a radius greater than 0.2 μm are found to control less than 40% of its porosity but contribute over 95% to its permeability. While pore size distribution remains relatively stable, average throat radius with the maximum frequency is decreased from 0.5 μm to 0.3 μm, resulting in a 13.9% decrease in average permeability. Compared to that of using pure brine, adding surfactants reduces the cutoff movable throat radius from 0.033 μm to 0.019 μm, leading to an incremental oil recovery of 4.26%. In a strongly water-wetting formation with its oil filling the center of a pore in the form of oil droplets, the movable water saturation in the two-phase flow zone on the relative permeability curves ranges from 22.5% to 55.1%. At the isotonic point, the water saturation is 43.6%, resulting in a waterflooding oil recovery of 42.1%. Conversely, in a weakly oil-wetting formation with its oil mainly distributing in the form of an oil film, water saturation in the two-phase flow zone varies from 22.3% to 48.1%. At the isotonic point, the water saturation is 38.1%, resulting in a waterflooding oil recovery of 33.2%. Experimental observations demonstrate that low salinity water (LSW) injection expands the electric double layer (EDL) on the oil/brine and rock/brine interfaces, altering the rock wettability; however, the presence of divalent ions in the LSW undermines such wettability alteration. On the other hand, permeability reduction resulting from salinity decrease can be alleviated by introducing divalent ions into the LSW, while continuous injection of monovalent brine reduces the ultimate oil recovery. Alternatively, a mixture of monovalent and divalent ions in LSW is utilized to revive permeability and maintain wettability alteration. Furthermore, an optimized divalent ion concentration is found to be conducive to reducing the cutoff throat radius and achieving a higher oil recovery in a tight sandstone reservoir.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".