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AAPG Bulletin

Abstract

AAPG Bulletin, V. 101, No. 11 (November 2017), P. 1859-1877.

Copyright ©2017. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/02071716191

Previous HitGulfNext Hit of Mexico Previous HitoverpressureNext Hit and clay diagenesis without unloading: An anomaly?

Richard W. Lahann1

1Indiana Geological Survey, 611 North Walnut Grove Avenue, Bloomington, Indiana 47405; rlahann@indiana.edu

ABSTRACT

Compaction disequilibrium is a widely accepted cause of Previous HitoverpressureNext Hit, especially in clay-rich, rapidly deposited sediments. Clay diagenesis has been associated with the occurrence of Previous HitoverpressureNext Hit greater than the compaction disequilibrium Previous HitoverpressureNext Hit. These observations have led to the expectation that Previous HitoverpressureNext Hit will be greater than the compaction disequilibrium contribution when clay diagenesis occurs within an overpressured mudstone.

Clay diagenesis have been reported in a Pliocene section of a well from the Previous HitGulfNext Hit of Mexico, offshore Louisiana. Pressure and log data from that well indicate that despite clay diagenesis, the Previous HitoverpressureNext Hit can be attributed solely to compaction disequilibrium.

This paper examines the whole mudstone and clay mineralogy composition and petrophysical characteristics of the offshore Louisiana well with clay diagenesis, but without a diagenesis contribution to Previous HitoverpressureNext Hit and contrasts that data with results from other clay diagenesis and petrophysical studies. The comparison suggests that the offshore Louisiana well was relatively smectite poor compared with wells from regions associated with a clay diagenesis contribution to Previous HitoverpressureNext Hit. The lower smectite content resulted in a lower percentage of reacted volume that was insufficient to allow the load transfer often associated with clay diagenesis. Petrophysical features of the offshore Louisiana well and nearby wells differ from the features associated with clay diagenesis in other Previous HitGulfNext Hit of Mexico wells and a limited number of international wells.

Comparison of location, age, depositional package, clay mineralogy, and petrophysical features suggests that provenance may control the occurrence of Previous HitGulfNext Hit of Mexico mudstones that do not experience increased Previous HitoverpressureNext Hit as a result of clay diagenesis.

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