--> Reducing the Errors and Uncertainties in the Petrophysical Analysis of Well Logs from Shaly Sand Reservoirs by Applying New Clay Typing Techniques, Chitale, Vivek D., #90100 (2009)
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Reducing the Errors and Uncertainties in the Petrophysical Analysis of Well Logs from Shaly Sand Reservoirs by Applying New Clay Typing Techniques

Chitale, Vivek D.1

1Halliburton, Houston, TX.

Geological and petrophysical description and characterization of shaly sand reservoirs needs to be as accurate as possible especially in the “expensive to operate” deep Previous HitwaterNext Hit basins globally. This paper shows how the errors and uncertainties involved in the interpretation of the well logs from shaly sand reservoirs can be reduced by means of a correct and meaningful application of clay science knowledge. The well log analysis thus performed enhances the accuracy in assessing the reservoir quality and compute fluid bulk volumes.

Simplified clay typing based on triple combo conventional logs is possible by using rationalized clay parameters for nuclear logs. Most common models for shaly sand reservoirs correct for clay Previous HitboundNext Hit Previous HitwaterNext Hit in shaly rocks, typically basing the “correction” on computed volume of clay or shale from logs, or from a laboratory-derived weight fraction of clay size particles in rocks (<4 microns). Now, considering that clay Previous HitboundNext Hit Previous HitwaterNext Hit (CBW) represents Previous HitwaterNext Hit of adsorption Previous HitboundTop to the surface of a given clay mineral, the “correction” should be done only if the rock actually contains a clay mineral characterized by sufficient quantity of CBW to affect the logs that need correction! Clearly, knowing clay type is essential before even selecting a formation evaluation model.

Using examples to validate these concepts, the paper highlights that clay mineral composition of a subsurface formation controls nuclear log responses -that essentially are bulk measurements - regardless of mode of distribution of constituent clays and whether they are digenetic or depositional. Implications of accurate clay typing for shale plays and tight gas sands is obvious in terms of achieving greater accuracy in predicting reservoir quality, calculating reserves, and reservoir modeling, thus helping reduce overall E&P risk. The paper shows examples from global reservoirs.


AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil