--> ABSTRACT: Distribution and Character of Complex Micropore Systems in the Eagle Ford Formation of South Texas, by Antia, Jonathan; Jennings, Debra ; #90142 (2012)

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Distribution and Character of Complex Micropore Systems in the Eagle Ford Formation of South Texas

Antia, Jonathan *1; Jennings, Debra 1
(1) Intergrated Reservoir Solutions Division, Core Laboratories, Houston, TX.

Detailed plane light and milled surface SEM petrographic studies of the Eagle Ford indicate that reservoir quality is controlled by complex micropore systems that reflect mineralogy, depositional fabric, grain type, organic content, and diagenesis. Cyclic interbedding of contrasting marl, limestone, and shale lithologies created strongly layered, heterogeneous reservoirs with poor recovery efficiency. Because depositional environment exerted a primary control on the reservoir rock types and subsequent diagenesis, their vertical stacking patterns reflect the complex interplay of high- (4th and 5th order) and intermediate-frequency (3rd order) stratigraphic sequences.

The most abundant pore types in marls occur within and between coccolith fragments. Organic nanopores (ONP) are most abundant and best developed in organic matter in marls with more porous fabrics. ONP also occur within foram chambers. Development of ONP appears to be favored by increased maturation of kerogen, as rocks with higher vitrinite reflectance typically have more ONP.

The limestones are generally influenced by tractive currents initiated by wave, tide and storm processes. These limestones are typically recrystallized, and are characterized by poorly developed intercrystalline and intraparticle pore systems. The degree of recrystallization appears to be the predominant control over the abundance, connectivity, and size of intrinsic pores present in these intervals. Few ONP are associated with recrystallized intervals; this is likely related to the paucity of organic matter in these intervals caused by oxidation and sedimentologic winnowing.

Differences in the relative abundance of pore types in any given interval appear to be controlled by the ratio of recrystallized limestones and marls which is largely a product of the depositional facies (i.e. proximal vs. medial or distal facies), stratigraphic stacking patterns, and the abundance or organic matter and clay in the matrix. Depositional facies in the Eagle Ford are predictably stacked in small- and larger-scale stratigraphic sequences that are recognizable throughout this study. Understanding the distribution and type of porosity within the Eagle Ford allows the regional characterization of reservoir rocks and the development of predictive exploration models.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California