Bibliographic record
Abstract
Abstract VSP surveys provide the best way to measure anisotropic parameters for formations with transverse isotropy. Two types of anisotropic parameters can be determined from a walkaway VSP survey: effective parameters for overburden formations above and below VSP receivers, and local parameters for formations within the depth range of a receiver array. Each type has advantages and disadvantages. We use a case study to demonstrate the determination of these two types of anisotropic parameters and use them to build anisotropic depth profiles. Walkaway VSP data were acquired offshore East Coast Canada. The receiver array was centered at a depth of 2051 m and covered a vertical depth range of 143 m. The survey well was deviated 46 °from vertical at the array and rotated 61 ° from the plane of the shot lines. The maximum sourcereceiver offset was 4000 m. Effective anisotropic parameters were calculated from direct and reflected P-wave traveltimes using traveltime inversion. Local anisotropic parameters were computed from the direct P-wave data using a local phase slowness analysis technique. The estimated effective anisotropic parameters Õand ?were 3.7% and 16.7% for the overburden. The estimated local parameters Õ and e were 5.6% and 20.7% over the receiver depth range, confirmed by the interval parameters computed using traveltime inversion for the same depth range. The effective parameters Õand?were -1.9% and 23.8% for the formations just below the array. Combinations of these parameters, in conjunction with well log and seismic data, were used to build anisotropic profiles. This case study shows that the joint use of local slowness and traveltime inversion methods reliably allows theextraction and maximization of anisotropy information from walkaway VSP data. It provides a means to build anisotropic profiles that best approximate formation anisotropy. Introduction Transverse Isotropy with a Vertical symmetry axis (TIV or VTI) is a relatively common type of anisotropy observed in seismic data. A walkaway VSP (WVSP) has a wide angular aperture and well-determined direct arrivals. By placing receivers within the suspected anisotropic zone, a walkaway VSP offers the best dataset available for in-situ seismic anisotropy measurements. Three parameters define weak P-wave anisotropy in a general VTI medium; the P-wave velocity in the direction of the symmetry axis, V0, and the Thomsen parameters Õand ? 1. For horizontally layered VTI formations, the vertical interval velocity function Vv obtained in a VSP velocity survey is a good approximation for V0. The anisotropic parameters Õand ?can be determined from WVSP traveltime and polarization data using a variety of techniques 2, 3, 4. Three sets of anisotropic parameters can be determined from WVSP; effective parameters for overburden formationsabove VSP receivers, local parameters for formations within the depth range of a receiver array, and effective parameters for formations below the array. In practice, receivers are usually placed in a small depth range in the borehole because of acquisition constraints and economic conditions. In such cases, local anisotropic parameters can be derived for a limited depth range.
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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 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".