Microfracturing during primary migration in shales

Abstract

In several geological environments, chemical reactions are coupled to rock deformation and the associated stresses induced locally interact with the far field loading. This is the case in immature shales that undergo burial and diagenesis, where the organic matter evolves with temperature into hydrocarbons which induces local volume expansion. At large scale, this mechanism is responsible for the transport of hydrocarbons from source to reservoir rocks, a process referred to as primary migration. However, how the interactions between local fluid production, microfracturing, and transport are coupled remain to be understood. Here, we analyze this coupling phenomenon by developing a discrete element model where the generation of local overpressures occurring in kerogen patches is simulated, while the surrounding rock is subjected to external loading. It is shown that, due to local fluid overpressure; microfracturing occurs and brings the fluids to migrate through the medium. The numerical results are confirmed by laboratory experiments where the network of microfractures induced in an immature Green River shale sample heated under small differential stress was imaged in three dimensions using X-ray microtomography. Moreover, the numerical simulations identify that the state of differential stress and the initial kerogen distribution constitute two key parameters that control the formation of the three-dimensional percolating microfracture network and could thus explain primary migration in shale rocks.

Deformation Experiments on Bowland and Posidonia Shale—Part II: Creep Behavior at In Situ pc–T Conditions

“…However, recorded production curves of fractured wells typically exhibit a rapid decline within the first few years (Hughes 2013;Wang 2016; Al-Rbeawi 2018) as a result of reservoir depletion and fracture closure due to time-dependent proppant embedment (Sone and Zoback 2014;Wang 2016;Cerasi et al 2017). Fracture closure is influenced by temperature (Johnston 1987;Brantut et al 2013;Masri et al 2014), confining pressure (Niandou et al 1997;Petley 1999;Naumann et al 2007;Kuila et al 2011;Islam and Skalle 2013;Brantut et al 2013), stress conditions (Swan et al 1989;Chong and Boresi 1990;Ibanez and Kronenberg 1993;Kwon and Kronenberg 1994;Brantut et al 2013;Sone and Zoback 2013a;Rybacki et al 2015Rybacki et al , 2017, and mechanical and petrophysical properties (Brantut et al 2013;Rybacki et al 2016;Cerasi et al 2017;Morley et al 2017;Teixeira et al 2017).…”

Deformation Experiments on Bowland and Posidonia Shale—Part I: Strength and Young’s Modulus at Ambient and In Situ pc–T Conditions

“…However, the production rate of a fractured well typically declines over time (Al-Rbeawi 2018; Wang 2016), due to depletion of the reservoir and possibly due to fracture closure processes (Cerasi et al 2017;Wang 2016). Fracture closure is affected by confining pressure (Niandou et al 1997;Petley 1999;Naumann et al 2007;Kuila et al 2011;Islam and Skalle 2013), temperature (Johnston 1987;Masri et al 2014), non-isostatic stress conditions (Swan et al 1989;Chong and Boresi 1990;Ibanez and Kronenberg 1993;Kwon and Kronenberg 1994;Sone and Zoback 2013a;Rybacki et al 2015Rybacki et al , 2017 and petrophysical and mechanical properties such as mineralogy, porosity, permeability and brittleness of the reservoir rocks (Rybacki et al 2016;Morley et al 2017;Li et al 2017;Teixeira et al 2017;Cerasi et al 2017). Therefore, knowledge of the geomechanical behavior of shale rocks with respect to the above-mentioned parameters is important to better understand their fracture closure behavior (Morley et al 2017;Ilgen et al 2017;Kikumoto et al 2017;Li et al 2017;Cerasi et al 2017).…”

Synchrotron tomographic quantification of strain and fracture during simulated thermal maturation of an organic‐rich shale, UK Kimmeridge Clay

“…[] used synchrotron tomography to characterize and describe the dynamics and patterns of cracks at microscale. Their work demonstrated the potential power of sCT in such field and how the data can be used to model the fracture behavior during heating overpressuring [ Teixeira et al ., ]; however, no 3‐D strain mapping was performed.…”