HIGH FREQUENCY BOREHOLE SEISMIC ACQUISITION AND ITS APPLICATIONS FOR RESERVOIR DELINEATION OF THE BUNYU FIELD, ONSHORE KALIMANTAN, INDONESIA

摘要

Precise reservoir delineation requires high frequency seismic data to understand detailed reservoir architecture. This should be supported by an accurate knowledge of stratigraphy, structure, lithology, porosity, fluids and faulting is required. Well log data contributes essential information to achieve this knowledge, however reservoir properties may vary significantly between wells. Surface seismic data plays a significant role in deriving the reservoir static model that integrates the geological and geophysical data. Seismic attributes such as amplitude, frequency, and phase can reveal reservoir properties such as lithology and fluids. However, surface seismic data may be lacking or of too poor quality to derive reservoir properties and guide in-fill development drilling. Furthermore, the ability of surface seismic data to delineate reservoir properties is limited by its resolution, which is a function of its low frequency content. The main advantage of borehole seismic is that the reflected waves are recorded with much less interference and attenuation compared to surface seismic measurements and therefore a higher resolution can be achieved. In this paper, we present the application of high frequency borehole seismic imaging in the Bunyu Field, onshore Kalimantan, Indonesia. The 2D seismic data in the field is very sparse and of very poor quality due to near surface noise masking the reservoir image. The objective of this study was to delineate fault location and reservoir extension away from the well, and to evaluate rock properties such as lithology and fluids using high frequency borehole seismic data. Fundamental information is provided on VSP methodology, planning of VSP acquisition, its acquisition and processing, and the interpretation of the final data set. The VSP results revealed precise location of the fault that was observed 450 m away from the well, compared to 200m as originally interpreted, adding significant gas reserve. Offset VSP image also identified a bright spot at a greater depth and away from the well that based on seismic attributes analysis could be a target for new a drilling location. The VSP methodology provided a cost-effective approach to accurate reservoir definition in a rather challenging environment.