Optimum Timing for Miscible CO<sub>2</sub>-EOR after Waterflooding in a Tight Sandstone Formation
Bibliographic record
Abstract
In this paper, CO 2 dissolution into a light oil/reservoir brine and optimum timing for CO 2 enhanced oil recovery (CO 2 -EOR) after waterflooding in a tight sandstone formation are experimentally studied. First, the gas–oil ratio (GOR) of CO 2 -saturated light oil and the gas–water ratio (GWR) of CO 2 -saturated reservoir brine are measured by using a PVT system. The measured GOR is found to be approximately six times of the measured GWR at the same pressure and temperature. Second, the equilibrium interfacial tensions (IFTs) between the light oil/reservoir brine and CO 2 are measured at different equilibrium pressures and the actual reservoir temperature by applying the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case. The measured equilibrium IFT between the light oil and CO 2 is about one-third to one tenth of that between the reservoir brine and CO 2 under the same test conditions. Third, the minimum miscibility pressure (MMP) between the light oil and CO 2 is determined to be 11.0 MPa from the measured equilibrium IFTs by using the vanishing interfacial tension (VIT) technique. Lastly, a total of five coreflood tests are performed to determine the optimum timing for miscible CO 2 -EOR after waterflooding. All five tests are conducted at the same production pressure of 12.0 MPa to ensure that CO 2 flooding is miscible. In comparison with CO 2 secondary flooding, CO 2 tertiary flooding has a much delayed CO 2 breakthrough (BT) because the initially injected water substantially reduces the mobility of the subsequently injected CO 2 . Accordingly, the oil recovery factor (RF) of CO 2 flooding in terms of the residual-oil-in-place (ROIP) is much higher. By comparing the total oil RF of waterflooding and CO 2 flooding in terms of the original-oil-in-place (OOIP), the oil RF of CO 2 flooding in terms of the ROIP, and the pore volume (PV) of CO 2 BT from the beginning of CO 2 flooding, it is found that the optimum timing for starting miscible CO 2 tertiary flooding is when waterflooding reaches half of its maximum secondary oil RF.
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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 | 0.001 |
| 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".