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Processing the Hod 3D multicomponent OBS survey, comparing parallel and orthogonal acquisition geometries

BP, Sunbury-On-Thames, England, U.K.

Bruno Gratacos and Ron Evans

CGG Americas, Brentford, England, U.K.

Corresponding author: kommedj@bp.com

The first 20% of the full text of this article appears below.

The Hod 3D multicomponent ocean-bottom seismic (OBS) survey was acquired to image the reservoir through a gas cloud. Data were acquired with shot lines both along the receiver cables (in-line or parallel shooting) and orthogonal to the receiver cables (cross-line shooting).

This gave us an opportunity to compare the seismic images produced from these shooting geometries to see if there is factual support for the rumors that parallel shooting results in better converted PS-wave images than orthogonal shooting. In the following we use the term C-wave for a wave that propagates as a P-wave from the source to the reflector at which point it converts and propagates to the receiver as an S-wave.

Both techniques have previously been used with success. Orthogonal shooting has been used to image through gas clouds at Valhall Field and Lomond Field. In-line shooting has been used at Alba Field. At Hod, the mobilization cost was fixed, and the incremental cost of adding orthogonal shooting to the parallel shooting was about 25% of the total cost.

Hod Field is in the central graben in the Norwegian sector of the North Sea, approximately 13 km south of Valhall Field and northeast of the major regional Skrubbe fault (Figure 1). The field has two anticlinal structures, East and West Hod. Similar to Valhall, the West Hod structure is obscured by gas in the overburden, although not as severely. The West Hod structure is an elongated anticline, with the major axis in the east-west direction (Figure 2). By orienting the receiver cables orthogonal to the major axis of the anticline, the structure was covered with four deployments—each with four cables. Acquisition parameters are given in Table 1. Data were not sampled even finer due to the limited number of receiver cables available. (Decreasing . . . [Full Text of this Article]