Seismic Investigation of Monotonic and Constant Pressure Hydraulic Fracturing Schemes in Granite
Authors: Butt Awais , Hedayat Ahmadreza , Moradian Omid 
Published: August 2024

ABSTRACT:
The conventional monotonic hydraulic fracturing (MN-HF) with continuous injection rate till breakdown has potentially shown to be sub-optimal in controlling HF propagation and ensuring efficient production in some HF operations. Alternatively, constant pressure hydraulic fracturing (CP-HF), operating under a pressure lower than the formation's breakdown pressure, offers advantages potentially reducing environmental impact and costs. However, additional research integrating real-time monitoring techniques is necessary to improve our understanding of HF phenomena and fracture characteristics of these injection schemes. This study involves HF of Barre-granite with combined active-passive monitoring using gear-oil injected under MN-HF and CP-HF injection schemes. The concentration of microseismic events in planar regions suggested formation of a single planar fracture through MN-HF. Conversely, CP-HF resulted in a wider distribution of microseismicity and tortuous HF with numerous branches which is in favor of permeability enhancement for projects such as Enhanced Geothermal Systems (EGS). For CP-HF, generated microseismicity was reduced and aseismic deformation processes detected by active monitoring were more pronounced than in MN-HF. This study emphasizes HF initiation and propagation processes associated with MN-HF and CP-HF stimulation schemes, providing valuable insights for more accurate characterization of the stimulation operation.

1. INTRODUCTION
Adopting multi-stage HF in extended horizontal wells has revolutionized the global oil and natural gas industry. Multi-stage HF offers several advantages to single-stage stimulation, ranging from increased reservoir contact and drainage to enhanced recovery and production (Dusseault and McLennan, 2011; Economides et al. 1991; Giger, 1985). This technology has the potential for comparable influence in geothermal applications (McClure et al. 2022), where HF in ultra-low permeability hot dry reservoir rock can be mandatory to increase the efficiency and production for cost-effective thermal resource extraction (Breede et al. 2013). However, employing the conventional HF procedure, which entails pumping fluid at a consistent rate (monotonic) till the formation breakdown, has shown to be suboptimal for multi-stage HF. The monotonic fluid injection has resulted in non-uniform HF growth in different stages. This can be attributed primarily to HF being created in one stage affecting the propagation of HF from neighboring stages (stress shadowing), reducing overall effectiveness and recovery (Bunger and Cardella, 2015; Roussel and Sharma, 2011; Roussel et al. 2012; Seth et al. 2021; Yoon et al. 2015). Also, the monotonic injection approach in multi-stage HF involves increased water usage and wastewater production/disposal. HF has been associated with induced seismicity; a phenomenon that has been demonstrated to correlate directly with the injected fluid volume (McGarr, 2014). The risk of triggering damaging earthquakes may increase with the intensity and frequency of fracturing operations in multi-stage projects with monotonic injection methods.