A Method to Measure Ultralow Permeabilities of Shale Core in Multiple Directions Using Pressure-Pulse Decay Technique
Bibliographic record
Abstract
Abstract Permeability is a very critical tight reservoir parameter to characterize the process of oil/gas storage and production. In particular, distinct anisotropy of the shale reservoir, demands a practical method to measure permeabilities in multiple directions using the same core. In this work, a systematic and practical pressure-pulse decay (PPD) technique is given to determine ultralow permeabilities of shale reservoir core in a cell with finite volume. The test gas can be non-adsorption gas such as helium or adsorption gas such as methane. As described herein, given appropriate assumptions, the mathematical models based on the corresponding designed experiments (non-adsorption gas or adsorption gas) are formulated, and the exact solutions for the corresponding mathematical models are proposed using Laplace transform. Approximation techniques are further given to analyze experimental data to obtain radial and axial permeabilities. It is found that there are distinct anisotropy of shale reservoir and the permeability may be smaller when adsorption gas is used instead of non-adsorption gas. Compared with traditional two-chamber PPD techniques, its advantages mainly lie in three points: only the pressure in one chamber is measured, which can lead to fewer pressure transducers and easier experimental operation. Meanwhile, the center of shale core needs not be drilled when the radial permeability is measured. What's more, the whole measurement is based on the same core and more information of the core can be obtained. However, it should also be noted that there is about 1 MPa difference of effective stress between our axial experiments and radial experiments. The effect of this difference on permeability is typically less than 5%, so the modified PPD can detect anisotropy efficiently.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| 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".