Evaluating the Pressure-Dependent Equivalent Permeability Evolutions for Shale Matrix: Experiments and Modeling
Bibliographic record
Abstract
Abstract The ability to model and predict matrix permeability changes during reservoir depletion is critical for accurate analysis of long-term production performance in unconventional gas reservoirs (UGRs), including shale gas and coalbed methane reservoirs. Yet, flow quantification in the nanoporous matrix is still challenging due to the complex pore structure and morphology. To understand the pressure-dependent matrix permeability evolution, this study conducted laboratory permeability measurements using pulverized samples. Equivalent permeability was estimated from the pressure decay profile for the Devonian shale sample. A novel experimental system, a differential volumetric unit, has been established and applied to capture the accurate transient gas flows for the shale sample. The measured permeability of shale exhibited overall decreasing trends with pressure depletion. Due to the presence of slip flow and Knudsen diffusion, low-pore-pressure data did not follow the same decline trend fitted by high-pore-pressure data as observed in the shale sample. This study also utilized methane as the invasion fluid to examine the adsorption effect on matrix permeability, whose value could be up to 40% lower than permeability without correction for adsorption because of the condensation of adsorbed phase at pore surface occupying available pore space. Since these tight rock matrixes are composed of micro- and nanopores, matrix permeability is primarily related to pore structure (e.g., the pore size distribution, porosity and tortuosity). Low-pressure N2 adsorption was conducted to characterize the complex pore structure of the Marcellus shale sample. A multimechanic model was proposed to predict the pressure-dependent matrix permeability based on pore structure information and investigate the effect of gas adsorption on apparent permeability. This model has successfully linked the realistic, complex pore structure with the pressure-dependent matrix permeability of shale and coal. The proposed model could be coupled into the commercially available simulator to forecast long-term production profiles for UGRs wells.
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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 | 0.001 | 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 | 0.001 | 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".