Microbiology of Oil- and Natural Gas-Producing Shale Formations: An Overview

Abstract

Shales are the most abundant type of sedimentary rock on Earth. Many shale formations contain high concentrations of organic matter and can serve as both sources and reservoirs of oil and natural gas. Oil-and natural gas-producing shale formations are characterized by very low permeability and extremely small pore throat sizes, which have traditionally made it very difficult to extract economic volumes of hydrocarbons. Recent advances associated with horizontal drilling and hydraulic fracturing have led to increased exploration and extraction of oil and natural gas in shale formations throughout the world. This increased activity in shale formations has been accompanied by a variety of microbial-related issues including reservoir plugging, reservoir souring, sulfidogenesis, and corrosion. Even though it is clear that microorganisms cause a wide variety of deleterious processes in shales, very little is known about their origins in these formations. There are several plausible sources of microorganisms in shale, including the formation itself and the fluids that are used during the drilling and hydraulic fracturing processes. This chapter contains an overview of what is currently known about the microbiological properties of shale formations and the fluids that are used during the drilling and hydraulic fracturing processes. The chapter also contains a brief description of the research issues that need to be addressed in future studies.