Unconventional Shale reservoirs, with typically ultra-low permeabilities, have been a major focus of hydrocarbon production over the past few decades. In this paper, we investigated the effect of biogeomechanical altered near-wellbore properties on hydrocarbon recovery from tight formations, using Niobrara shale samples. We first obtained the mechanical and elastic properties of Niobrara shale samples using the scratch test method. Subsequently, we treated the core sample with a cultured microbial solution at distinct conditions. Further, we obtained the new geomechanical properties impacted by the process. Finally, we showed the potential impact of this altered near-wellbore properties on hydrocarbon recovery from the Niobrara shale formation. Our results suggest that in Niobrara shale reservoirs, biogeomechanical alterations of near-wellbore properties could potentially (1.) impact the mechanical, microstructural and mineralogical properties, (2.) reduce its mechanical integrity, and (3.) improve hydrocarbon recovery from Niobrara shales in addition to other stimulation techniques.

1 Introduction

Biogeomechanics is the scientific study of how biological processes influence the mechanical properties and behavior of rock and soil (Kolawole et al., 2021). Few studies have attempted to investigate the effect of biological processes on the geochemical (Abdel Aal et al., 2004; Atekwana et al., 2006), physical and mechanical properties of unconsolidated sandstones (Kalish et al., 1964; Phillips et al., 2015; Hudyma et al., 2018), carbonates (Raleigh and Flock, 1965), and minerals (Mueller and Défago, 2006).

The bacterium Clostridium acetobutylicum (ATCC® 824) (Sreekumar et al., 2015) is utilized for this study, and it is also known as "Weizmann Organism". In a research study (Banat, 1995), molasses were injected together with Clostridium acetobutylicum into sandstone rock samples, the metabolism action of the bacteria increased the reservoir permeability, and hence significantly improved oil recovery. In a microbial enhanced oil recovery (MEOR) study (Van Hamme et al., 2003), the in-situ growth and metabolism action of Clostridium acetobutylicum reduced the interfacial tension and increased microscopic oil-displacement efficiency, hence improving hydrocarbon recovery. The study further established that the synthesis of organic acid metabolite by Clostridium species dissolves the minerals-grain bond (cementation) in reservoir rocks, and increases pressure and permeability.

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