Abstract

During drilling operations fractures can be induced for a number of different reasons. When such a situation occurs it may be the favoured option to sidetrack from a shallower depth. In order to avoid intercepting the fracture it is useful to be able to model the plane of the fracture to inform sidetrack trajectory design. This paper will demonstrate an integrated approach to the design of such trajectories using the following techniques.

  • Determination of maximum horizontal stress (SH) Orientation: This is obtained from a variety of sources. Caliper logs, Image logs, LWD image logs, and X-dipole sonic are all interpreted to provide the direction of SHmax

  • Validation of SHmax orientation: The above techniques are valid in near-vertical wells with deviation up to 20°. At higher deviations an understanding of the magnitude of SHmax is required. SHmax needs to be high enough to support the premise that breakout orientations still reflect the SHmax orientation at the higher deviations encountered. This validation is obtained by Geomechanical modelling which is calibrated to observations of breakout orientation and width.

  • Fracture Detection: As well as knowing the orientation of the fracture it is important to identify the location and extent. The loss interval can be detected using time-lapse LWD resistivity. The as-drilled resistivity logs can be compared with repeat passes of resistivity logs post-losses to identify the loss interval. This can then be compared with the suspected loss zone from pre-drill pore pressure-fracture gradient (PPFG) model.

  • Sidetrack Trajectory Design: Once the location and orientation of the fracture are known a model of the existing wellbore and fracture can be made. The trajectory of the sidetrack can be chosen to minimize the possibility of encountering the fracture and repeating the loss event.

Several examples will be presented where by following the proposed workflow sidetracks have been successfully drilled without issue.

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