--> ABSTRACT: Characterization of Low Contrast/Low Resistivity Reservoirs with Modem Imaging Tools: Example from the Gulf of Mexico, by D. L. Eubanks and M. Oraby; #91021 (2010)

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Characterization of Low Contrast/Low Resistivity Reservoirs with Modem Imaging Tools: Example from the Gulf of Mexico

EUBANKS, DARRELL L. and MOUSTAFA ORABY

A challenge to any geologist exploring for hydrocarbons in the Gulf of Mexico area, either onshore or offshore, is to locate and identify potential low contrast/low resistivity reservoirs. Low contrast/low resistivity reservoirs can be defined in the Gulf Coast as those showing very little resistivity contrast between shales and sands. Many Gulf Coast LC/LR sand reservoirs have resistivity value of less than 2 ohmms with some as low as .7 ohmms.

Sands that makeup LC/LR generally fall into three categorizes: 1) Clean very fine grained sands, 2) Laminated sands and shales, and 3) Sands with dispersed clays. The depositional environments that developed these sands are common throughout the Gulf of Mexico. This accounts for the wide distributions of LC/LR reservoirs in the gulf.

Conventional log analysis techniques used to evaluate LC/LR reservoirs calculate very high water-saturation values and are common reasons for potential pay zones to be by-passed or unrecognized. These methods do not take into account the high irreducible water associated with the fine grained sediment or laminated sand/shale sequences that makeup LC/LR reservoirs.

Modern borehole imaging tools such as electrical micro imaging (EMI) and magnetic resonance image logging (MR/L) allow the characterization of LC/LR reservoirs as to the grain size, fluid types and mobility, and internal clay distribution. Examples of EMI and MR/L from the Gulf of Mexico show that important information needed to understanding and identifying LC/LR reservoir can be obtained.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.