4D-Close-the-Loop Workflow to Calibrate the Geomechanical Simulation Model and Identify Drilling Geohazards: Field Application

摘要

Anomalous time shift observations from 4D seismic data shot in an HPHT field in the North Sea are being investigated. We are using these time shift signatures to understand the dynamic geomechanical behaviors of two major shales units (Shale I and Shale II) between the main producing sands. To capture the geomechanical and pressure diffusion behavior in these shale units, we have performed a coupled fluid flow and geomechanical simulation. Next, we use a 4D-Close-the-Loop workflow to integrate reservoir simulation results, the rock physics model, and seismic signature into a comprehensive and iterative process to update the simulation model. In this process, geomechanical modeling and the conversion of model results to synthetic 4D seismic time shifts allow for a quantitative comparison of synthetic response with the observed 4D seismic anomaly. The application of this hands-on approach has prompted the calibration of the fluid flow and the geomechanical properties of different reservoir units. Consequently, a better match between the modeled 4D seismic time shifts and those observed from the field data has been achieved. Furthermore, this calibration provides a model that more reliably predicts the pore pressure and stress tensor changes, allowing more confidence in selecting safe well paths. The calibrated geomechanical model suggests that Shale I, which is a silty marine shale, undergoes pressure diffusion, and therefore, the trapping mechanism of Shale I is highly uncertain. The clay-rich Shale II, however, acts as an effective pressure barrier, and hence it is overpressured relative to the surrounding formations and could be a high-risk formation for future drilling programs. In this case study, the application of the 4D-close-the-loop workflow allows the calibration of the geomechanical model, and hence a close examination of stress distribution at the level of Shale I and Shale II. These findings have provided additional information that could identify potential geohazards and prevent the risk of well deformation and failure.