Effect of pore-throat structure on irreducible water saturation and gas seepage capacity in a multilayer tight sandstone gas reservoir
Bibliographic record
Abstract
In this study, effects of pore-throat structure on gas seepage capacity in a multilayer tight sandstone gas reservoir and the interlayer interference characteristics during commingled multilayer production have been experimentally investigated. More specifically, representative core samples were selected from a multilayer tight sandstone gas reservoir in the eastern Ordos Basin according to a statistical analysis of various cores with respect to their petrophysical properties. Then, high-pressure mercury intrusion (HPMI) experiments were conducted to obtain capillary pressure curves of core samples collected from each layer, while their corresponding pore-throat structure characteristics were evaluated based on median throat radius, cutoff throat volume ratio, pore-throat skewness, and fractal dimension. Subsequently, combined with the nuclear magnetic resonance (NMR) technique, gas-water seepage experiments with the collected core samples of each layer were performed to obtain the relative permeability curves and T 2 spectrum distribution curves. Considering the effect of pore-throat structure heterogeneity and water saturation on gas slippage, gas relative permeabilities of core samples were corrected. According to irreducible water saturation distribution, gas relative permeability together with water locking damage coefficient, irreducible water saturation and gas seepage capacity of each layer were quantitatively assessed. In addition, depletion experiments from single- and two-layer cores were conducted to examine the impact of pressure differences and pore-throat structure variations on interlayer interference. The heterogeneity of throats is found to be the main factor dominating irreducible water saturation. With the aggravating heterogeneity in the pore-throat structure, there exists an increase in irreducible water saturation and water locking saturation. Irreducible water is principally distributed in small pores/throats controlled by capillary force, leading to a more serious water locking phenomenon. With a decrease in proportion of small throats and a reduction in structure heterogeneity of large throats, irreducible water mainly occupies as a form of membrane in large pores/throats whose proportion and heterogeneity are the key to gas seepage capacity. With an increase in proportion of large throats and a reduction in their structure heterogeneity, the damage coefficient due to water locking becomes smaller, gas relative permeability at the irreducible water saturation increases, and the gas seepage capacity is enhanced. With a deterioration of pore-throat structures, irreducible water saturation increases, water locking phenomenon intensifies, and gas seepage capacity is weakened. The increase in disparity of interlayer pore-throat structure leads to heightened levels of interlayer interference. The interlayer pressure differentials play a crucial role in determining the extent of interlayer interference in a commingled multilayer production process. In a high-pressure layer, its gas flow rate initially remains relatively high, resulting in a rapid decline in the pressure gradient within the core at the outlet region. In a low-pressure layer, however, water locking is exacerbated by the backflow, thereby reducing the gas seepage capacity in the outlet region and ultimately diminishing its gas production rate. Differences in pore-throat structure are a significant factor affecting interlayer interference. The more pronounced the discrepancy in pore-throat structure between layers, the more severe the impact on the interlayer interference, and subsequently the lower the gas production rate. • HPMI and NMR tests are used to examine effect of pore-throat structure on irreducible water saturation and gas seepage capacity. • Based on pore-throat structure heterogeneity and gas slippage, gas relative permeabilities of core samples are corrected. • The proportion and heterogeneity of small throats are found to be the main factors dominating irreducible water saturation. • Pore-throat structures (i.e., size and heterogeneity of throats) dictate irreducible water saturation and gas seepage capacity. • Interlayer differences in pore pressures lead to different interlayer interferences during commingled production.
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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 | 0.000 |
| 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 | 0.001 |
| 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 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".