Impact of Microbes on Reservoir Quality

Abstract

It has long been recognized that temperature is a major factor in controlling mineral dissolution and creating secondary porosity in reservoirs. But, what about alteration that occurs soon after deposition? Studies of modern and low temperature ancient sandstones suggests that microbial processes play a very important early role in diagenesis which impacts both conventional and unconventional reservoir quality. Initial mineral dissolution, the development of early carbonate cements, and the formation of early clay grain coats, all appear to be influenced by microbial activity at near surface conditions. Recognizing and understanding these processes is key to improved diagenetic modeling. Examples showing the influence of microbes on early diagenesis will be shown from a variety of modern depositional settings. For example, SEM/EDS studies of modern fluvial sandstones show the presence of thin, transparent "saran-like" biofilms which appear to act as a glue attaching clay to grains to form early clay coats and also promoting the precipitation of early carbonate cement. Other examples include the partial dissolution of feldspar and mafic minerals to form early intragranular "secondary porosity" in a tropical delta, the binding of sand grains in a modern shrimp burrow, and the alteration of basalt in a contaminated aquifer.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015