Combining Wireline and LWD Borehole Seismic Data for Drilling HPHT Well: A Novel Approach

Abstract

Abstract A unique integrated borehole seismic technique was used to access and mitigate drilling risk on a Petronas Carigali highpressure, high-temperature (HPHT) exploration well offshore Sabah. The approach combined wireline vertical seismic profiling (VSP) and logging-while-drilling (LWD) seismic surveys to look ahead for pore-pressure prediction, geostopping, and obtaining high-resolution seismic imaging below the well path. Three wireline VSP runs and one seismic-while-drilling run were made. The first-run rig-source VSP at the 13 3/8-in. section was used to obtain an initial velocity model and early prediction ahead of bit and imaging. This was followed by a wireline vertical incident VSP (VIVSP) run at the 9 5/8-in. section to refine the pore pressure prediction and for target illumination. LWD seismic was deployed while drilling the following 8 3/8-in. section to provide real-time checkshots for pore-pressure constraint and geostopping above a key formation top to set casing. Both the wireline and LWD VIVSP showed minor faults that were not apparent on the 3D surface seismic; these faults explain the unusual kick encountered. This high-resolution image was used to decide the sidetrack path. The final rig-source VSP was logged at total depth (TD) to complement the pore-pressure prediction and seismic imaging. In addition, the real-time checkshots while drilling aided in stopping drilling to within a stand (less than 30 m) above the key formation top. The depth uncertainty of the key formation was over 130 m prior to drilling. Introduction Integrating wireline and LWD borehole seismic information for drilling is a new technique in Malaysia, first applied by PETRONAS Carigali Sdn Bhd, a subsidiary of PETRONAS. In this novel approach, we will demonstrate how borehole seismic data, which is conventionally used for geologic and geophysical interpretation, has added value for drilling and well planning. The PETRONAS well, drilled in 2008, is located 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 previously made drilling difficult, generating hazardous incidents including stuck and lost-inhole pipe, losses, and kicks. These incidents had resulted in stopping drilling prematurely of the wells at great cost to PETRONAS, and also left the ultradeep targets unexplored. Studies by the PETRONAS 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 was inadequate for this purpose.