Abstract

3D seismic data provides high resolution images of subsurface hydrocarbon reservoirs in Widuri Field. These images give information on gross sandstone body geometry, together with details related to their internal architecture. The images are combined with well data to show how preserved sand body geometries have changed through geological time in Widuri Field. Widuri reservoirs dominantly comprise laterally restricted fluvial sandstone bodies associated with meandering channels, and form part of the Oligocene-Miocene Upper Talang Akar Formation on the northern flank of the Asri Basin. A range of techniques is used to image and interpret sandstone body geometry from the 3D seismic data. Certain techniques are suited to specific reservoirs, due largely to differences in stratigraphic setting.

Narrow, highly sinuous channel geometries, approximately 100-200 m wide, are imaged within many of the reservoir sandstone bodies, using 3D seismic. Where these features are clearly imaged, they commonly meander laterally between opposed margins of a sandstone body, and are interpreted to be fluvial channels responsible for adjacent sand deposition. In many cases these features are thought to represent abandoned channel mudstone fill, and may locally compartmentalize single reservoirs. The approximate 100-200 m width of these preserved channels is thought to be closely related to the dimensions of individual depositional units that make up a particular sandstone body. Although preserved gross sandstone body geometry appears to have changed markedly through geological time, the width of these narrow channels varies only slightly. This suggests that some of the differences in preserved sandstone body width are controlled by meander belt width and differences in rates of channel avulsion versus rates of deposition, rather than due to large changes in channel dimensions. An increase in wavelength of the channels is accompanied by a small increase in channel width through geological time, and coincides with a general change to more distal depositional environments with greater tidal influence.