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3D geometry corrections Disclosure Number: IPCOM000238411D
Publication Date: 2014-Aug-25
Document File: 7 page(s) / 417K

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The Prior Art Database

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Title: 3D geometry corrections


In most formulations of the refraction statics problem it is a requirement that shots and receivers should be positioned along the straight line and shot's positions should coincide with some of the receiver's positions. Data-driven interferometric approach to refraction statics solution and near surface model building without first-break picking is based on these critical assumptions.

These conditions are not met in the geometry of the 3D surveys and 2D crooked lines

The technique may use time stretching and squeezing technique to transform the 3D data into an equivalent 2D case thereby allowing the implementation of the conventional straight line interferometric solution to build near-surface depth model and derive static corrections.

Detailed Description

Uncorrected variations in the thickness and velocity of the weathered layer affect substantially the quality of the images of deep reflectors of land seismic data. Therefore the goal of a refraction solution is to obtain an accurate near-surface model from refraction data and to replace variable low velocity with the velocity below weathering to improve the resolution of the seismic data.

Most refraction solutions, used in land seismic data processing, utilize first-break pick times to derive a near-surface model. Based on newer methods of refraction imaging ([1], [2]) which do not require first-break picking, a data-driven interferometric approach [3] for 2D surface seismic data was developed to obtain near-surface modeland compute refraction statics corrections. This approach allows eliminate one of the most time-
consuming steps, namely first-break picking by utilizing the first-arrival
signal instead of the scalar first-break pick times.

Critical assumptions for this method such as: seismic survey is acquired along straight lines with receivers regularly distributed along the line, shot positions coincide with at least some receiver positions, does not allow application on 3D data, crooked lines or sparse surveys. Violation of these conditions will lead to incoherent stacking, deteriorated images, and therefore unreliable near-surface model.

To build the near-surface depth model we generate refraction convolution stack (RCS) [1], a common-receiver image of the delay times of several shallow seismic refractors and refraction velocity stack (RVS), a time image of the spatial variations of seismic refraction velocity for the same refractors [2].The horizons are then picked on both RCS and RVS images and the near-surface depth model is obtained using Snell's law.

To obtain delay times the RCS is generated by convolving trace S1-R1 with the trace S2-R1 and cross-correlating the result with the trace S1-S2, assuming that there is a receiver at the position of the shot S2 (Figure 1). Resulting traces are stacked over all available shots combinations.

Refraction Convolution Stack (RCS) trace:

( ) ∑ ( ) ( ) ( )

where: - cross-correlatio...