Successful acquisition and interpretation of VSP data using LWD technology

Abstract

Downhole logging provides critical information for assessing the reservoir, and planning field development. In the case of complex well trajectories, conventional wireline logging presents operational risks that can be avoided with data acquisition using logging-while-drilling (LWD) technology. Seismic while drilling is a technology which can acquire borehole seismic during drilling, delivering real time check shots and waveforms in real time with lookahead capabilities. For the drilling of a significantly deviated well in the Northern Dampier Sub-Basin, offshore Australia, a vertical incidence vertical seismic profile (VSP) was acquired utilizing this seismic while drilling technology in lieu of wireline data. The key objectives of the VSP data were to calibrate the seismic time-to-depth relationship and image the reservoir to support detailed interpretation of the internal reservoir structure. Acquisition of the VSP data was performed while pulling out of the hole after the well had reached target depth. Due to the deviated well geometry, an additional vessel was used to deploy the seismic source — this ensured the seismic source was positioned vertically above each receiver location (walk-above or vertical incidence VSP). Processing of the VSP followed a routine walk-above VSP processing workflow, including tool orientation, multicomponent wave field separation, multiple and noise suppression, and stacking. Deliverables included a traditional velocity report, corridor stack and the unstacked up-going wavefield, useful for interrogating internal reservoir structure. This VSP survey delivered good results, the multicomponent seismic VSP provided a robust seismic to well tie, and the image obtained has contributed to improved reservoir understanding in the Fletcher East Oil Field. This type of acquisition is cost effective and recommended for the acquisition of VSP data in highly deviated wells.