Evaluation of a Rapid Diagnostic Tool to Estimate Geometry Evolution of Multiple Simultaneously Propagating Fractures from Cross-Well Fiber Optic Strain Measurements

Abstract

Cross-well low-frequency distributed acoustic sensing (LF-DAS) strain rate measurements generate data useful for hydraulic fracture diagnostics. These data contain information about hydraulic fracture geometry; however, interpreting the data has relied on time-consuming and computationally expensive numerical interpretation methods. This study aims to evaluate the applicability of a rapid diagnostic tool, known as the "zero strain rate location method" (ZSRLM), for characterizing the geometry of multiple fractures propagating simultaneously. Simulations of multiple fracture propagation are conducted using a planar 3D multi-fracture simulator that incorporates 3D rock deformation, fluid flow in the wellbore, fluid leak-off, and multi-scale fracture propagation regimes. A super-time-stepping algorithm is employed to solve the nonlinear parabolic equations governing fluid-driven fractures. The far-field strain profile induced by multiple propagating fractures along a cross-well fiber optic cable is computed using the displacement discontinuity method. Various scenarios are simulated by adjusting key completion parameters, including the number of clusters, cluster spacing, in-situ stress states, and geomechanical properties. The ZSRLM is then applied to the computed strain field to estimate fracture extents and propagation rates. The accuracy of the ZSRLM is assessed by comparing the estimated fracture geometry parameters with the known simulated values. Our observations indicate that the ZSRLM is not effective when two or more fractures approach the observation well at similar times, as it becomes challenging to discern unique strain-rate converging patterns on waterfall plots for each fracture. However, when fracture arrivals at the monitor well are offset, distinct strain rate patterns emerge, enabling the application of the ZSRLM. Errors between simulated and estimated fracture extent propagation rates are quantified. Finally, the ZSRLM is applied to a field case involving multi-cluster fracture propagation, and the interpretation of the results is discussed in light of these findings. This research demonstrates the applicability of the ZSRLM for diagnosing the velocities and final extents of multiple fractures propagating simultaneously. The method offers a rapid means of characterizing stimulations using cross-well LF-DAS measurements, which can inform decisions regarding completion design, well spacing, and landing zone. The study contributes to the advancement of efficient fracture diagnostics in the industry, reducing the reliance numerical interpretation methods.