The planning phase is key to a successful relief well operation. The goal for this planning phase is to produce a comprehensive project plan, which defines all processes and activities required to meet the final objective. The relief well team, a multidisciplinary team with roles and responsibilities clearly defined at each phase, should undertake live simulation drills to identify any gaps and implementation redundancies.  

Designing the optimum relief well trajectory requires going from the interception window derived from intensive dynamic fluid modeling to the surface location while respecting the directional constraints, the well architecture constraints, taking into consideration the surface exclusion zone, and incorporating a selection of ranging technologies through single or multiple technologies deployment.

Locating the target well requires the use of ranging techniques. Positive detection requires deriving the relative position between the relief well and the target well by measuring the distance and direction from the relief well to the target well. The locate phase is based on a strategy that allows for investigating the total area of the potential detection zone.

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The range of this zone mainly depends on the size of the combined Ellipsoid of Uncertainty (EOU) and the expected ranging detection distance. In the worst-case scenario where the target well has not been detected as expected, a new zone for investigation is defined and a new plan is developed accordingly.

It is only by having positive detection of the target well that the ranging technique capabilities can be confirmed. Thus, it is important to monitor closely the potential magnetic interferences by analyzing the available raw data (near-bit direction and inclination packages, measurement while drilling (MWD)), to ensure a safe approach toward the target well until the positive detection of the target well exists.

The positive detection of the target well allows for reinitializing the relative uncertainty between the target well and the relief well, and is likely to require a new relief well plan to comply with the ranging results. This procedure needs to be performed under the relief well constraints as defined in the planning phase (directional and ranging considerations, interception constraints, etc.).

The interception phase is the final objective in drilling a relief well which is intercepting the target well. The interception angle depends on the communication option chosen; either parallel positioning between the target and relief well in the case of perforating, high-incidence angle in the case of direct intercept, or low-incidence angle in the case of reentry into a milled window.

During this phase, the distance between the relief well and the target well is very small. It is important to use advanced 3D simulation tools to model the interception, considering the relative positioning between the wellbores and all possible scenarios for the final approach until the soft touch.

3D reverse ranging engineering process allows to modify the target well surveys to correspond to the ranging calls and improve the relative positioning between the intercepting well and the target well. Understanding the directional behavior of the target well from the 3D reverse ranging process is key to ensure a successful intercept on first attempt.

Killing Operations:

Following the successful interception phase, the first step of the killing operation phase is to successfully establish communication between the relief well and the target well by hydraulic communication, milling, or perforating. In this latter case, performing perforating simulations is recommended to select the perforating gun size, density, orientation, and the resulting penetration diameter into the target well casing. In addition, for a high-profile relief well, it is recommended that surface tests be performed to validate the final option.

If the milling option is selected,  modelling the milling operation is important, including the detailed description of the milling assembly, the relative positioning between wellbores, and the completion dimensions. The milling modelling allows for assessing the milled window characteristics (shape, length, width, flow area, etc.) in different possible scenarios, with the objective being to simplify the decision making  in selecting  the best operational milling parameters.

Following successful milling operation, kill mud is pumped into the target well to stop the flow. The kill mud properties are defined at the planning phase based on the killing simulations (density, volume, flow rate, etc.). The objective of stabilizing the well process is to allow for reducing the high-pumping rate used in the pump-to-kill step to a reasonable level until the target well is stable. Kill mud continues to be injected while carefully monitoring the pressure and mud volume.

Plug & Abandon:

This final phase of the relief well process aims to properly plug and abandon the target well in a secured manner. The plugging requirements depend on the local regulatory bodies, but the general objective is to inject cement into the target well to ensure that the productive zone is permanently isolated. Bridge plugs could be required in addition in some cases. Pressure tests are undertaken to ensure target well integrity.