Zero-Offset DAS-VSP FWI: Data & Processing Checklist

🌐 中文版 / Chinese version

Worksheet for full-waveform inversion of zero-offset DAS-VSP data. Nine main steps; each row lists the operation, the data it requires, and its product. Data providers can match deliveries against the “Data required” column. Primary target is near-well Vp; optional extensions are Q and anisotropy.

1. Data specifications

Required

Data	Key requirements	Format
Raw DAS shot gathers	Per shot per channel, unstacked, undenoised; plus a preprocessed version with its flow documented; headers must carry shot coordinates, channel number, MD, offset, sample interval, start time; header byte map attached	SEG-Y preferred; HDF5 / TDMS / SEG-D accepted
DAS acquisition parameters	Sample rate, record length, channel spacing, gauge length, pulse rate, interrogator model and firmware, physical quantity and units, gain and polarity, cable installation and fiber type, known coupling issues	Document
Source information	Source type; per-shot coordinates and offsets; sweep parameters; pilot or correlated wavelet; shot times and synchronization; number of sweeps per point, single-sweep records preferred	Document + SEG-Y/ASCII
Well information	Trajectory MD/TVD/x/y/inclination/azimuth; wellhead coordinates, elevation, KB; casing program; cable top/bottom depth; channel-depth calibration table and method	CSV or Excel
Well logs	DT, DTS, density, gamma, caliper, temperature	LAS
Initial-model data	Checkshot time-depth; interval velocities; velocity volume through the well; formation tops	SEG-Y / ASCII
Metadata	CRS and projection; unit system; time datum; polarity convention; record of prior processing	Document

Recommended

Data	Purpose
Geometry files SPS or UKOOA P1/90	Geometry cross-check
Statics	Near-surface correction
Ambient-noise records without shooting	Step 0 SNR assessment
Acquisition report and observer logs	Tracing anomalous channels
Legacy VSP products: corridor stack, up/downgoing fields	Steps 7A/8 reference
Surface seismic section through the well, prior velocity or Q results	Step 8 validation
Walkaway / multi-offset / multi-azimuth shots	Step 9 extensions, high value

2. Processing sequence

#	Step	Operation	Data required	Product
0	Data reception & QC	Verify trace headers, CRS, units, polarity; SNR and usable bandwidth statistics per shot and per depth interval	Raw DAS shot gathers; header byte map; metadata; ambient-noise records	QC report; usable shot/channel list
1	Channel-depth calibration	Map channel numbers to MD/TVD using tap tests, casing collars, known markers	Calibration table; well trajectory; casing program; cable installed depth	Channel-depth table
2	DAS preprocessing	Remove bad channels and poorly coupled intervals; suppress common-mode noise and cable ringing; unify polarity; strain-rate/strain conversion as needed	Full acquisition parameters: gauge length, channel spacing, physical quantity and units, gain and polarity, cable installation, coupling notes	Clean shot gathers
3	First-break picking	Pick direct-arrival first breaks on every channel	Clean gathers; shot times and synchronization scheme	First-break table
4	Initial model & tie	Compare first-break traveltimes with checkshot and sonic; build 1-D starting Vp	Checkshot; sonic DT/DTS; density; interval velocities or velocity volume; formation tops	Initial Vp model
5	Wavefield separation	Flatten on first breaks -> extract downgoing field by median/FK/SVD -> subtract to obtain upgoing field	Clean gathers; first-break table	Downgoing and upgoing wavefields
6	Wavelet extraction	Window the downgoing direct arrival to extract the measured source wavelet; cross-check against the pilot-correlated wavelet	Downgoing field; pilot sweep; single-sweep records; sweep parameters	Measured source wavelet
7A	Conventional branch	Deterministic deconvolution of upgoing by downgoing - compresses the wavelet and removes downgoing multiples; corridor stack	Up/downgoing wavefields	Corridor stack as reference
7B	FWI main line	Forward modeling = Green function of the current model convolved with the measured wavelet; DAS strain operator in the objective; iterate near-well Vp, optionally invert the source term	Initial model; measured wavelet; clean gathers or upgoing field; channel-depth table; trajectory	Near-well Vp model
8	Validation	Compare inverted Vp with sonic, checkshot, corridor stack; residual analysis	Products of steps 4 and 7A; legacy VSP results	Validation report
9	Optional extensions	Q estimation if bandwidth allows; VTI parameters if walkaway or multi-offset shots exist	Multi-offset gathers and their geometry files	Q profile; VTI parameters

3. Delivery formats

Data type	Preferred	Alternative
DAS gathers	SEG-Y	HDF5, TDMS, SEG-D
Wavelet / pilot	SEG-Y	ASCII
Well logs	LAS	CSV
Trajectory / calibration	CSV	Excel
Geometry	SPS	UKOOA
Velocity / horizons	SEG-Y	ASCII
Parameters & notes	PDF or Markdown	Word

4. Reservoir data framework for future 4D coupling

If time-lapse VSP/DAS observations are later coupled to the reservoir model for seismic-constrained history matching, the following reservoir-side data will be needed. Not required now; listed in advance so the data channel can be planned.

Category	Content	Format
Static model	Corner-point grid, porosity/permeability/saturation properties, faults, zonation	GRDECL / EGRID
Dynamic model	Full simulation deck: PVT, relative permeability, initialization, schedule; or at minimum per-timestep pressure and saturation restarts	Eclipse-style DATA / INIT / UNRST
Production history	Rates and injection by well, bottom-hole pressures, RFT/MDT points, well-test interpretations	CSV / Excel
Rock-physics calibration	Core elastic measurements, dry-frame moduli; DT/DTS/density logs shared with Section 2	Report + LAS
Time-lapse alignment	Restart file of the reservoir state at each VSP/DAS acquisition date	UNRST

Coupling route: two simulated states pass through Gassmann fluid substitution to give delta-Vp, compared against time-lapse VSP/DAS observations; the residual enters ensemble history matching as an observation term.