Identifying Microbial Reef Fabric Types and Their Digenetic Properties at Little Cedar Creek Field, Conecuh County, Alabama

Ganganath Koralegedara and William C. Parcell
Wichita State University, Wichita, Kansas

Examination of depositional fabrics and associated diagenetic characteristics provide insights into resulting reservoir quality distribution in the Jurassic Smackover microbial reef reservoirs at Little Cedar Creek Field (LCCF), Alabama.

Heydari and Baria (2005) and Mancini et al. (2006) identified six Smackover lithofacies in the field. All facies were interpreted to form in shallow water, within 3 miles of the paleoshoreline. All these facies can be identified in the fully developed southwest region of the LCCF.

Two different microbial fabric types (after Parcell, 2002) can be identified in the thrombolite boundstone in LCCF. They are layered thrombolite (type I) and chaotic thrombolite (type II). Layers in type I are thicker and textures of type II are similar respective to the type I and type II of the five thrombolite fabric types identified by Parcell (2002). Type I is associated with centimeter scale microbial layers interbedded with lime mudstone. Density and core porosities of type I varies from 2-7% while type II porosity values are >5%. Type II characterized by equal lateral and vertical thrombolite fabric growth and it produces a good reservoir rock. Evidence of thrombolitic textures and peloids are often preserved as moldic and vuggy pores. Dolomitization in the type II is limited to limestone cement replacement and void boundary fill with polymodal planar subhedral. In the southwest of the field, unimodal planar euhedral dolomite form in voids and void boundaries. In addition, some of the peloids are partial replaced by the dolomite leaving the original moldic texture.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas