Combining Wireline and LWD Borehole-Seismic Data for Drilling an HP/HT Well

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper IPTC 13083, ’Combining Wireline and LWD Borehole Seismic Data for Drilling an HP/HT Well: A Novel Approach,’ by T.K. Lim, SPE, and Aqil Ahmed, SPE, Schlumberger, and Gunawan Taslim and Muhammad Antonia Gibrata, SPE, Petronas, prepared for the 2009 International Petroleum Technology Conference, Doha, Qatar, 7-9 December. An integrated borehole-seismic technique was used to access and mitigate drilling risk on a high-pressure/high-temperature (HP/HT) exploration well offshore Sabah, Malaysia. The approach combined wireline vertical seismic profiling (VSP) with logging-while-drilling (LWD) seismic surveys to predict pore pressure, determine geo-stopping, and obtain high-resolution seismic imaging beyond the well path. This high-resolution image was used to select the sidetrack path. The final rig-source VSP was logged at total depth (TD) to complement the pore-pressure prediction and seismic imaging. Introduction Integrating wireline and LWD bore-hole-seismic information for drilling is a new technique in Malaysia. In this approach, borehole-seismic data, which are used conventionally for geologic and geophysical interpretation, have added value for drilling and well planning. The well, drilled in 2008, is off the coast of Sabah, East Malaysia. The target reservoir, in contrast to most other reservoirs in the region, is deeper, hotter, and at much higher pressures than normal. Pore-pressure ramps and depleted sands in the field had made drilling difficult previously, generating hazardous incidents including stuck and in-hole-lost pipe, fluid losses, and kicks. These incidents had resulted in stopping drilling prematurely, resulting in ultradeep targets remaining unexplored. Studies by the sedimentologist suggested that this overpressure hazard is associated with undercompacted bathyal mudstone, and the well-casing design required accurate prediction. The well path was designed to avoid the regional fault that could complicate pore-pressure prediction. Existing surface-seismic and distant-well-based velocity control were inadequate for this purpose. Primary well objectives were the lightly explored, stacked, lowstand Upper Miocene turbidite-reservoir sequences. The deepest of these were expected to be at approximately 4000- to 5000-m sub-sea (SS) depth. The shallow units, which are depleted because of production from other locations, were at approximately 2500- to 4000-m SS depth.