Hydraulic fracture monitoring: Integrated analysis of borehole logs, seismic reflectivity, microseismicity, ISIP analysis and PKN modelling.
Creators: Mirzayeva, Tahmina
Publisher: name: University of Alberta Library
Year: 2024

<p>Hydraulic fracturing operations in Montney formation present challenges due to anomalous microseismic behavior and inconsistent cloud patterns. Fracture propagation is mostly uni-directional, moving predominantly towards the northeast. However, some stages exhibit behavior contrary to this trend. The overall cloud pattern is inconsistent, lacking a clear explanation for such phenomena. This study aims to use different types of datasets to explain the behavior of fracture propagation in the Montney formation. Therefore, this study aims to elucidate the dynamics of fracture propagation through four key objectives: assessing fracture treatment parameters, unraveling microseismic behavior mechanisms, exploring the link between microseismic events and geological features, and investigating stress shadow effects.</p>

<p>Employing the Perkins-Kern-Nordgren (PKN) model alongside novel parameters, including variation in fracture height and plain strain modulus, we analyze fracture treatment parameters (Perkins &amp; Kern, 1961). Using the PKN model, we calculate the fracture half-length and compare it with the microseismic cloud fracture length to understand the link between treatment parameters and actual fracture propagation. The PKN fracture length estimation is mostly affected by the fracture duration,<br>
showing a small correlation between the PKN and microseismic cloud lengths, suggesting that higher duration may affect the results. However, there are significant discrepancies between the results, with PKN overestimating the fracture length, which is normal due to the simplicity of the PKN approach. The observed anomalies suggest additional factors influencing propagation behavior beyond treatment parameters alone.</p>

<p>Later, we used Microseismic Analysis to understand the general pattern of cloud propagation and trajectories and explore possible causes of unidirectional propagation. Microseismic events revealed that most propagation occurs toward the northeast, although some stages show a tendency toward the southwest after some stages. To investigate unidirectional propagation, we applied a magnitude filter, considering that it might be due to the distance between treatment well and monitoring well. Results revealed that this is not the cause; the magnitude cut-off only affected the cloud thickness. We also interpreted r-t plots, revealing the existence of ”Normal,” ”halted-growth,” and ”Reactivation” patterns. Later, we used r-t plots and applied a model-based approach to understand fracture length propagation over time by fitting the model equation. By doing so, we have defined the regimes of fracture treatment with time-dependency relationships. We found that regimes on the northeast side are mostly storage-dominated, while those on the southwest are mostly leak-off dominated.</p>

<p>Integration of borehole logs and seismic reflectivity data underscores the influence of geological features on fracture propagation. Natural fractures and pore pressure changes emerge as significant contributors to variation in fracture patterns, emphasizing their strategic importance. Using the FMI logs, we identified natural fractures and bedding planes around the wellbore. The ”Reactivation” pattern observed was because of the existence of open fractures. We also analyzed that the well has landed in different horizons. On the other hand, reflectivity analysis using seismic attributes (dip, azimuth, minimum and maximum curvature) and pore pressure maps helped us understand that fractures tend to move in the up-dip direction. Moreover, there are zones identified as high-pressure zones forcing fractures to move predominantly in the northeast direction.</p>

<p>When a single planar fracture is created, it increases the stresses around it due to the fracture opening. Such changes in stress are called ”stress shadow.” The stress shadow affects fracture propagation, as it may cause changes in horizontal stresses, leading to differential fracture propagation. For instance, when horizontal stresses are flipped, fractures tend to move toward the next stage. Therefore, we applied the Stress Escalation Model using Instantaneous Shut-In Pressure data by Roussel (2017). We found that stress reorientation is not the case; however, stress shadow might be the cause of the change in cloud patterns, as uni-directional propagation increases stress shadow on one side of the well, affecting subsequent stages to move in the opposite direction.</p>

<p>This comprehensive analysis emphasizes the interplay of treatment parameters, geology, and stress effects on hydraulic fracture propagation. These findings contribute to optimizing hydraulic fracturing strategies and enhancing reservoir management practices for more sustainable energy extraction from unconventional reservoirs.</p>