Wettability Alteration during Low-Salinity Waterflooding and the Relevance of Divalent Ions in This Process
Bibliographic record
Abstract
From laboratory and field test results, it is now largely agreed that reducing the overall salinity, especially the concentration of divalent ions of the injected water, can markedly improve the oil recovery. However, as a result of the complexity of the crude oil–brine–rock (COBR) system, there is no clear explanation of why the divalent cations (Ca 2+ ) are of major significance in a low-salinity water effect (LSWE). In the present paper, spontaneous imbibition, ζ-potential measurements, static adsorption/desorption of benzoic acid (BA) onto crushed Berea, and BA self-assembled layers on silica wafer have been performed to correlate macroscopic wettability alteration during low-saline water flood with the microscopic release of the hydrophobic layers (organic acid layers) on mineral surfaces and explain the relevance of active cations (Ca 2+ ) in this process, thereby providing a better understanding of the underlying mechanisms of a LSWE. Spontaneous imbibition results show that initial wettability of the COBR system was dominantly controlled by the initial concentration of Ca 2+ rather than Na + in brine; i.e., the initial wettability changed to be more oil-wet with an increasing concentration of CaCl 2 in initial water, while changing the concentration of NaCl in initial water had little effect on initial wettability. Moreover, reducing salinity of imbibing brine can outstandingly improve oil recovery of cores aged by CaCl 2 brine, whereas no obvious enhanced oil recovery (EOR) by low-salinity water was observed for cores aged by NaCl brine. Decreasing the concentration of either CaCl 2 or NaCl brine was able to make the oil/brine and brine/rock interfaces become less positively charged or even more negatively charged, observed by ζ-potential measurements, resulting in increased electrostatic repulsive forces between the oil/brine and brine/rock interfaces. These results suggest that the anionic groups of organic acid from crude oil, such as carboxylate, adsorb onto negatively charged mineral surfaces mainly through calcium bridges instead of van der Waals forces or sodium bridges and reducing salinity is able to increase the electrostatic repulsive forces between mineral surfaces and carboxylate groups and then break calcium bridges to change the wettability of the rock surface to be less oil-wet, and as a result, EOR occurs. These suggestions were supported by the static adsorption/desorption studies and self-assembly experiments. After sorption to crushed Berea, the varied BA concentration in the supernatant analyzed by total organic carbon (TOC) reveals that the presence of the background electrolyte Ca 2+ largely enhanced sorption in comparison to Na + . Lowering salinity was able to desorb BA from crushed Berea. Field emission scanning electron microscopy (FESEM) was used to obtain the microchemical composition and morphology of the wafer surface interacted with BA under different ionic strengths and solution cations (Ca 2+ and Na + ). Ca 2+ ions were found to enhance the adsorption of BA self-assembled layers on a silica wafer compared to Na +, which directly demonstrates that BA molecules mainly self-assemble on SiO 2 by calcium bridges rather than sodium bridges or van der Waals forces. The BA self-assembled layers were released after immersing organo-wafer into deionized water.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".