Maximum Flooding Surfaces – They Key to Successful Laterals in Shale Wells.
Walter W. Wornardt, PhD
President and Chief Geologist Micro-Strat, Inc.
Eagle Ford, Austin and Taylor Formations in South Texas are recognized by the highest occurrence of Calcareous Nannofossils and Foraminifers and log signatures. Their age ranges from the Cenomanian, Turonian, and Coniacian to Santonian and are correlated to Upper Cretaceous sequence stratigraphic cycle chart after Gradstein, 2010. Marker species and abundance peaks are correlated to the high gamma and low resistivity on well logs and continuous reflectors on seismic. This interval is the maximum flooding surface condensed section and its seismic expression is the maximum flooding surface. This interval is associated with high TOC, increased organic richness, providing major seals and time lines we use as mapping surfaces. Paleobathymetry for these formations is based on benthic foraminifers. Within the Eagle Ford, and Austin up to nine age datable maximum flooding surfaces are recognized regionally in sediments of Cenomanian, Turonian, Coniacian, and Santonian age. When drilling in the Eagle Ford it is important to accurately and consistently identify and correlate the same richness zone in two or more wells. In addition to logs and seismic using the maximum flooding surfaces identified in each well provides a third data set for identification of the same richness zone in each well. This zone will be located in-between the same age datable time lines, the maximum flooding surfaces. This methodology reduces risk in these expensive Eagleford wells by verifying that the lateral that is going to be drilled or has drilled is in the correct richness zone. Subsequently various types of maps, sand %, isopach, richness, and structural can be constructed using the MFS as control. The maximum flooding surfaces identified on well logs is based on the depth of the peak of the fossil abundances and its associated calcareous nannofossil and foraminiferal marker species which in turn should correlate to your continuous reflectors on seismic thus reducing risk.
AAPG Search and Discovery Article #90152©2012 AAPG Southwest Section Meeting, Fort Worth, Texas, 19-22 May 2012