Borehole and Reservoir projects

Strategic study of borehole data for land 3D design

This project involved analysing six 3-component VSPs and a large database of uphole surveys to help in designing and processing a series of 3D surveys. The VSPs showed an unusual frequency-dependent loss mechanism immediately above the target. We designed a non-linear sweep to combat these losses, which improved the resolution at the target relative to the previous 2D data. The uphole surveys were integrated with the VSPs and used to identify the main multiples and mode conversions so that they could be attenuated in data processing. Both datasets contained high amplitude source generated shear waves - studying these enabled us to optimise the design of vibratory and explosive sources for the planned 3D surveys.

Integration of borehole and surface seismic data for reservoir characterisation

This project was designed to provide the framework for a seismic reservoir study on a large onshore field. It involved:

• Performing a quality audit of the log and VSP data from 13 wells
• Re-datuming the log and VSP data in a consistent manner using a grid of uphole surveys
• Building a near-surface velocity model to assist in resolving long-period statics variations in the 3D survey
• Dephasing the 3D volume by matching to synthetic seismograms
• Re-interpreting the formation tops in time and depth on the log and VSP data
• Analysing the seismic response of the reservoir interval on the 3D seismic and VSP data

Use of log data to drive elastic modelling for a sub-basalt feasibility study

Vp/Vs ratios for basalts and sediments were needed for a project designed to investigate the use of mode-converted waves. No full wavetrain logs were available, so the shear velocities of the different rock types were estimated from P-wave, density, gamma and other logs. Finite-difference elastic modelling could then be used to predict the amplitudes of the various wave modes. A very different sub-basalt response was obtained using the full detail of the intra-basalt layering from the well logs, compared to several published models which treat the basalt as an homogeneous unit. The modelling was calibrated against recorded seismic data and played an important role in the interpretation and processing of mode conversions, as well as helping us to design the best acquisition technique for future seismic surveys.     

Borehole software

We offer a comprehensive log and VSP processing service using a combination of in-house and third party software, including:

• 2D and 3D modelling for VSP design using ray tracing, Zoeppritz plane wave or finite-difference elastic modelling
• Comprehensive processing suite for 3 component VSPs recorded with any geometry
• Wavelet extraction and dephasing of surface seismic data using synthetics and/or VSPs
• DIVINE - Transmission and reflection tomography and depth imaging by Dr. Ben Dyer. Crosshole, surface-to-borehole and surface seismic geometries.
• LogM - Log processing, synthetic seismogram and stratigraphic modelling system by GMA Inc.

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