- Copyright © 2002 Society of Exploration Geophysicists
This article expands on a pilot study by Ronghe and Trung (2000) which used impedance to delineate the extent of hydrocarbon occurrence in two sheet sand reservoirs.
The field, 45 km offshore Brunei Darussalam (Figure 1) in the Baram Delta province, is Neogene age. The stratigraphic succession is a northward-prograding sequence deposited in a series of cycles separated by marine transgressive phases (James, 1984; Sandal, 1996). Sand deposition is generally sheet-like and has been interpreted to be shoreface or delta-front related. The structural development of the offshore Baram Delta province was influenced by syn-sedimentary tectonics related to rapid and abundant sedimentation over a thick mud substratum. The field is within a growth fault zone and is associated with a prominent NE-SW trending growth fault (F1). All hydrocarbon-bearing blocks occur on the hanging wall side of this growth fault, dip to the north, and are separated by NE-SW trending normal faults. The NE part of the field includes a small pipe-like shale diapir intrusion. Data for this study comprised 166 km2 of 3-D seismic (line and trace spacing = 25 m) and wireline logs from six wells.
Figure 2 shows some wireline logs from well W3 and pressure measurements from repeat formation testing (RFT). The gamma-ray log indicates three prominent sand packages separated by shale intervals. The overall gamma-ray signature reflects the deltaic depositional response to sea-level fluctuations and subsidence. The sand packages indicate episodes of deltaic progradation and aggradation punctuated by sea-level transgressions and/or increased subsidence that caused shale deposition. The sonic velocity and density logs increase with depth, as expected, due to …