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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


24th Annual Convention Proceedings (Volume 2), 1995
Pages 181-189

Resolving MWD-Wireline Previous HitResistivityNext Hit Differences in Shaly-Sand Pay Zones

Steve Mack

Abstract

Recent experiences in offshore Indonesia using an MWD multiple depth of investigation Previous HitresistivityNext Hit sensor provided information about shaly sands which differed with the wireline dual laterolog run over the same intervals several days later. The difference in response between the two tools were substantial enough to cause differing results when utilising a log analysis program designed to determine prospective net pay. Analysis using the MWD log indicated that a marginal zone had low enough water saturation to be considered pay, in contrast to the wireline log analysis, which was more pessimistic. The cost of testing was debated but undertaken on the strength of the MWD evaluation. Good test results verified the MWD analysis, making a discovery out of a marginal zone. Substantial differences in calculated water saturation over several other reservoir sections were also the direct result of MWD-wireline Previous HitresistivityNext Hit discrepancies.

A comparison of the two technologies shows that the differences between the log responses can be explained by a combination of borehole and invasion corrections. After applying these corrections, the MWD response shows negligible changes to Previous HitapparentNext Hit Previous HitresistivityNext Hit (Ra), indicating that the raw response is very close to true Previous HitresistivityTop (Rt). In contrast, the dual laterolog required substantial corrections which led to errors in water saturation (Sw) of over 10 per cent.


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