Categorising Risk for Drilling and Completions Using High-Resolution Acoustic LWD Image Logs

Abstract

In extended reach and horizontal wells, it is critical to maintain borehole quality and stability to ensure efficient drilling and for the running and installation of completions. Categorising the risk of borehole degradation is becoming an important aspect of the well planning process. The quality of the borehole is affected primarily by geomechanical or drilling practices, which can significantly impact the life cycle and completion expenditure/cost of a well. We show examples of how recently available, high-resolution, acoustic logging-while-drilling (LWD) borehole image logs have enabled detailed characterisation of borehole shape to the extent that we can visualise and analyse all contributors to borehole stability. LWD measurements also enable the use of time-lapse logging; comparing images from the first pass with repeated logging runs at later stages in drilling to look for degradation in conditions of the borehole shape. These data can be used for several new or existing applications that can be split into two main categories: 1. drilling hazards – degrading borehole shape profiles, identification of borehole breakout and washed-out sections and 2. completions hazards – cement volume calculations, identification of trajectory and small-scale irregularities that could impair liner placement. These applications use zonation to describe all ranges in borehole trajectory, borehole shape and image artefact features for coding of the well during or shortly after drilling. This scheme is then combined with a geomechanics-centric integrated risk management workflow which provides an improved well planning process by identifying potential drilling and geological risks in each of the planed well sections. Pre-drill risk identification combined with visual verification of the borehole condition enables quick decision making for drilling and potential de-risking of subsequent wireline logging and completions operations, thereby allowing safe, predictable operations with minimal NPT, from drilling to completions. The enabling technology of high-resolution LWD acoustic imaging has made possible the visualisation of borehole shape features in detail previously not possible in either water or oil-based mud systems.