ADVANCES IN WIRELINE DATA ACQUISITION IN SYNTHETIC-BASED MUD SYSTEMS AND STRATEGIES FOR IMPROVED FORMATION EVALUATION

Abstract

With the growth in popularity of synthetic-based mud (SBM) systems in Australia, and the emergence of more advanced wireline logging tools, there is an expectation that better hole conditions will give rise to better value- for-money evaluation programs. This is certainly true from the drilling cost perspective, where a logging job can be completed without need for 'wiper' trips to recondition the hole. However, in order to extract maximum value from the latest generation of logging tools, careful attention needs to be applied to the formation evaluation program.

There have been some unexpected results from the wireline data quality viewpoint, with some positive results mixed with outcomes that fell below expectation, both linked to the complex nature of the synthetic-based mud recipes. Contrary to intuition, good quality electrical images may be obtained in synthetic-based muds, and some mud additives used to stop filtrate loss can seriously degrade the quality of acoustic images that are traditionally run in SBMs. Nuclear Magnetic Resonance works well in SBMs, especially where invasion is kept to a minimum. Holes drilled with SBMs do not normally display borehole ellipticity, which may be used to infer tectonic stress directions. However, oriented cross dipole shear-weave logging is able to detect azimuthal anisotropy, which may be related to tectonic stress, in holes with a circular profile.

There are trade-offs using different SBM recipes, which will impact on formation evaluation programs. Close consultation with the logging contractor and mud company, as far ahead of the drilling of the well as possible is recommended to ensure a satisfactory outcome.