Imaging Fractures Using Temperature Transients From Perturbation Analysis—A Novel Surveillance Technique Applied to the Belridge Diatomite
Bibliographic record
Abstract
Summary Results of a temperature transient analysis of data from Shell's diatomite steamdrive pilots are used to image hydraulic injection fracture lengths, angles, and heat injectivities into the low-permeability formation. The Phase I pilot is a limited-interval injection test. In Phase Π, steam is injected into two 350-ft upper and lower zones through separate hydraulic fractures. Temperature response of both pilots is monitored with 16 logging-observation wells. A perturbation analysis of the nonlinear pressure diffusion and heat-transport equations indicates that at a permeability of approximately 0.1 md or less, heat transport in the diatomite tends to be dominated by thermal diffusivity, and pressure diffusion is dominated by the ratio of thermal expansion to fluid compressibility. Under these conditions, the temperature observed at a logging-observation well is governed by a dimensionless quantity that depends on the perpendicular distance between the observation well and the hydraulic fracture divided by the square root of time. Using this dependence, a novel method is developed for imaging hydraulic-fracture geometry and relative heat injectivity from the temperature history of the pilot. The azimuth of the Phase I hydraulic fracture is determined to be 14° ± 2 N-NE. The azimuth of the Phase II upper hydraulic fracture is determined to be 16° ± 2 N-NE in the northern half of the pilot, and estimated to increase to 21° ± 2 in the southern half of the pilot. The azimuth of the lower hydraulic fracture averages 19° ± 4. The hydraulic fractures are found to be symmetric around both injectors, with an estimated length of 200 ft. Increased steam injection after the first year of pilot operations caused what is interpreted to be horizontal fractures toward the west in the G cycle and the east in the M cycle. These features are imaged to be at least 100 and 160 ft, respectively, along the hydraulic fracture azimuth. These conclusions are compared to tiltmeter data, microseismic data, and a simulation history match of pilot performance. Microseismic events recorded in the pilot are apparently not diagnostic of heat delivery to the formation.
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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 | 0.001 | 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".