Natural Fracture Compressibility and Permeability Hysteresis: Liquid vs. Gas
Notice bibliographique
Résumé
Abstract Natural fracture compressibility and permeability estimation is important for evaluating well performance for wells completed in unconventional hydrocarbon and enhanced geothermal energy systems exhibiting a complex fracture geometry where unpropped and natural fractures contribute to flow. This experimental study compares liquid and gas natural fracture compressibility and permeability hysteresis in low-permeability rocks, with examples from the Montney and Duvernay formations. A diverse suite of core plugs (horizontal), differing in lithology (siltstones/sandstones, organic/clay-rich shales), mineralogy (quartz/clay-rich), helium porosity (2-9%), and permeability (~0.0001-0.001 md) were analyzed. Core plugs were fractured under differential stress inside a biaxial core holder. Gas and liquid fracture permeability measurements were then performed at varying stress (500-4000 psi) under loading and unloading conditions representative of fluid depletion and injection, respectively. Assuming a planar fracture geometry and that the cubic law applies, fracture width and compressibility were then calculated using fracture permeability, stress data, and core plug dimensions. Water and liquid hydrocarbons were used for liquid permeability measurements. Natural fracture compressibility (gas: 5·10−5-5·10−4 psi−1; liquid: 1·10−5-7·10−4 psi−1), permeability (gas: >30 darcy; liquid: <30 darcy), and porosity (gas >8.5%; liquid: >8.5%) were consistently larger for gas than liquid. Interestingly, however, the hysteresis in fracture attributes (compressibility, permeability, and porosity) caused by loading/unloading was consistently larger for liquid than gas. Larger hysteresis for liquids is presumably due to the ‘softening’ effect on fracture asperities under stress, and elevated inelastic reduction in (fracture) roughness for liquids compared to gases. Notably, the average empirical (natural) fracture compressibility value commonly assumed in fracture modeling (~1·10−4 psi−1) falls within the range of measured fracture compressibility values (1·10−5-7·10−4 psi−1). However, experimental fracture compressibility values covered a broad range, as opposed to the widely accepted assumption of ‘average’ fracture compressibility adopted for modeling. Interestingly, for loading and unloading, fracture compressibility followed two distinct paths, regardless of fluid type. Fracture compressibility was consistently larger for loading than unloading. The latter observations suggest that larger degrees of hysteresis in complex fracture regions may occur for liquids than gases, and for injection versus production. Natural (and induced) fracture compressibility and permeability, while important controls on well performance for complex fracture cases, are challenging and time-consuming to measure for low-permeability rocks in the laboratory, particularly over multiple stress cycles. As a result, natural fracture compressibility and permeability hysteresis data are sparse in the literature. For low-permeability rocks, these data have been primarily measured with gas. The developed workflows and provided examples are beneficial for verifying empirical and analytical correlations used for evaluation of fracture compressibility and permeability, and their hysteresis in low-permeability sedimentary rocks.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».