Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Padgett, M. Articles by Menard, J. Search for Related Content GeoRef GeoRef Citation

Error analysis of a Garden Banks prospect's seismic imaging using a well and two sidetracks

Houston, Texas, U.S.

Corresponding author: MPadgett@quantum-earth.com

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

The Garden Banks well described below was drilled to test a seismic amplitude anomaly at 6.1 s two-way time (23 000 ft subsea). The original well found pay and was sidetracked twice for field size delineation. The first sidetrack drilled downdip and established an oil/water contact. The second sidetrack drilled updip to test an adjacent fault block. These three penetrations provide hard data with which to analyze the imaging errors of two prestack time migrations and one prestack depth migration of the prospect area with respect to fault placement and oil/water contact location.

Both prestack time migrations have "high amplitudes" below the oil/water contact and place the north-bounding fault too far north. These prestack time migrations would cause an operator to drill a dry hole "inside the amplitude," but downdip of the oil/water contact. The prestack depth migration contains a more accurate depiction of the hydrocarbon accumulation, position of the north fault, and location of the oil/water contact.

The prospect is in 2600 ft of water and is part of the general Llano-Auger minibasin system. The well targeted a seismic amplitude anomaly at 6.1 s associated with sands interpreted to be deposited in a deepwater sheet sand environment. The sands are interpreted to be trapped to the west by a salt weld/pinch out and trapped to the north by a down-to-the-south fault (Figure 1). The amplitude anomaly is not subsalt and dips are 23–26° ESE. Illumination studies have indicated that the anomaly should be well imaged by the data sets, though perhaps not optimally.

View larger version (36K): [in this window] [in a new window]   Figure 1. Structure and base map of the area around the Garden Banks discovery. Shown are the well with sidetracks and the basic structure with contours of 500 ft. The map is a combination of the well control and a generalized seismic interpretation beyond that control. . . . [Full Text of this Article]