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Frequency-enhanced imaging of stratigraphically complex, thin-bed reservoirs

A case study from South Marsh Island Block 128 Field

Pogo Producing Company, Houston, Texas., U.S.

Corresponding author: countiss@pogoproducing.com

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

Application of a poststack processing method that separates signal from noise, while enhancing only the high frequency "earth signal," helped identify new well locations in thinly bedded reservoirs that would not have otherwise been drilled. More importantly, wells drilled after application of this method added significant new reserves to a 27-year-old, offshore Gulf of Mexico field and nearly quadrupled daily production rates.

Numerous attempts have been made to image thin beds (<1/4 of dominant wavelength) by extracting higher frequencies from poststack seismic. Two common goals are: (1) define pinch outs of producing zones and (2) resolve internal bed geometries (lithofacies). This improved resolution is required during reservoir development. The most common poststack method is spectral whitening or boosting the amplitudes of all frequencies within a certain band-pass to the same level. The problem with this method is that it fails to discriminate noise from signal. Noise is boosted along with subsurface signal and, depending on the signal-to-noise ratio (SNR), may fail to extract the desired information. Other techniques such as coherence cube technology and seismic inversion help define some properties through a different approach but are limited by the inherent bandwidth of standard seismic.

	Case study—South Marsh Island

 
The discovery well for South Marsh Island Block 128 Field (Figure 1) was drilled in June 1974. The field is a stratigraphically complex, salt-cored, NW-SE trending anticline bounded on the west by a large down-to-the-west fault. The reservoir ranges in age from Angulogerina B (Early Pleistocene), to Lenticulina 1 (Late Pliocene), and lies between 4500 and 9000 ft subsea. Original depositional bathymetry encompasses inner neritic paleo depths at the younger, shallower horizons, to upper bathyal, in deeper zones. All reservoirs are normally pressured. At the beginning of this project the field had seven exploratory wells and 93 platform wells, including sidetracks, drilled from four . . . [Full Text of this Article]