Crushed-Rock Vs. Full-Diameter Core Samples for Water-Saturation Determination in a Tight-Gas Siltstone Play
Bibliographic record
Abstract
Summary The efficacy of crushed-rock samples vs. small plugs or full-diameter core samples for measurement of porosity, permeability, and fluid saturation is an important consideration in the evaluation of tight-gas reservoirs and shale-gas reservoirs. Crushed-rock core analysis methods originally developed for shale reservoirs are now, in some cases, being extended to low-quality tight-gas reservoirs. In this study, crushed-rock and full-diameter core measurements from two wells drilled with oil-based mud are compared to evaluate which of the two core-analysis methods is more reliable for water-saturation assessment of a major North American tight-gas siltstone play (Montney Formation, western Canada). Measurements from the studied full-diameter core samples have wide ranges of water saturation (10 to 45%) and bulk volume water (BVW) (0.5 to 2.6%). In contrast, measurements from crushed-rock samples have much narrower ranges of water saturation (10 to 20%) and BVW (0.2 to 0.7%). The lower values and limited range of water-content measurements from crushed-rock samples suggest a significant degree of artificial water loss during sample handling in the laboratory. This conclusion is supported by comparing core-measured BVW with deep-resistivity values from openhole well logs. Full-diameter BVW measurements correlate well with log resistivity, indicating they are generally representative of in-situ reservoir conditions. Crushed-rock BVW values, on the other hand, show no correlation with log resistivity. The results of this study suggest caution is warranted in the use of crushed-rock samples for water-saturation measurements of siltstones or silty shales. Failure to recognize artificial water loss from crushed-rock siltstone samples could lead to an erroneous interpretation of irreducible water saturation at in-situ reservoir conditions with potentially serious implications for resource evaluation and exploitation.
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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 | 0.001 |
| 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 | 0.000 |
| 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".