Investigating Fault-Sealing Effects on Pore Pressure Distribution, Induced Seismicity and Hydraulic Fracture Propagation: Numerical Modelling and Case Study in Northeastern British Columbia
Creators: name: Esmaeilzadeh, Zahra
Publisher: name: Science
Year: 2023
Subjects: subject: Sealing fault
subject: Pore Pressure
subject: Induced Seismicity
subject: Hydraulic Fracturing
subject: Numerical Modelling
subject: Northeastern British Columbia
subject: Geomechanics
subject: Geomechanical modelling
subject: Statistical Analysis
subject: Education--Sciences
subject: Geophysics
subject: FOS: Earth and related environmental sciences
subject: Energy
subject: Engineering--Petroleum

description: This thesis focuses on the effects of sealing faults and associated lateral pore-pressure gradients on induced seismicity and hydraulic fracturing (HF) operations. The studied formation is the Montney, a Triassic geological unit located in the Western Canada Sedimentary Basin that hosts one of the most productive unconventional plays in the world. The study area is located in northeastern British Columbia (BC), situated within the Kiskatinaw seismic monitoring and mitigation area (KSMMA), in the Septimus field where a significant induced earthquake sequence occurred in November 2018. Previously published reports show that pore pressure in the Montney Formation is compartmentalized, indicating that permeable and impermeable features such as fractures and sealing faults may control the reservoir fluid flow. Notably, the locations of pressure discontinuities are generally consistent with known faults, supporting a previous hypothesis that pressure compartments are fault-bounded. This thesis tests this hypothesis and models the effects of a horizontal pressure gradient (∆P) on fault activation and hydraulic fracture propagation. Novel methodologies have been developed for investigating complex interactions between pore-pressure gradient, seismicity and hydraulic fracturing mechanism, consisting of three workflows based, respectively, on statistical analysis of pore-pressure data, numerical simulation of hydraulic fracturing, and numerical modelling of fault activation. First, a comprehensive reservoir model is considered to characterize regional hydrodynamic, petrophysical and mechanical properties. The compiled data are used to construct a new pressure map of the Montney Formation, yielding insights into relationships between pressure boundaries and seismicity. The results confirm that pressure discontinuities are generally fault-bounded, but seal preservation depends on depth and fault properties. Earthquakes (both induced and natural) appear to cluster preferentially in areas of a high lateral pore-pressure difference. Next, using grid oriented hydraulic fracture extension replicator (GOHFER) software, HF growth is modelled in the presence of an impermeable fault and surrounding permeable damage zone. Different scenarios are considered based on ∆P and damage-zone properties. Results show that fault sealing behaviour depends on the pressure difference, stage shadowing effects, fault throw, injection rate and fault damage-zone permeability. The adverse effects of a damage zone on fluid loss of injected fluid are more pronounced when there is a lateral pressure gradient across the fault. The order of importance of these parameters implied by the modelling results is: stress shadowing &gt; lateral pressure gradient &gt; fault seal properties. Finally, the effect of lateral pressure gradient on fault activation is tested using 3D distinct element code (3DEC) software- 3D numerical modelling code that simulates the mechanical response of rock mass with discontinuities such as fractures and faults. Using this tool, sensitivity analysis of fault activation is performed based on the presence or absence of a significant pressure difference and a highly fractured and permeable damage zone on both sides of the fault. Strong ∆P may lead to asymmetric fracture geometry and considerable leakage of pore pressure into the lower pressure domain. A damage zone around the fault appears to channel pore pressure along the fault, leading to a more uniform distribution of fault aperture and pore pressure than in the absence of a damage zone, where the fault opening is concentrated near the HF intersection.