Thermal Transients

Equipment in a water injection well was not functioning as expected and the working hypothesis was that thermal conditions were responsible. Engenya was tasked with determining what those conditions were likely to be. This required the transient simulation of the shut in, startup and steady operational conditions of the well. The result of one of the cases investigated with this simulation is shown in the banner above, starting with the steady geothermal gradient that would exist at shut in conditions, simulating the injection of cold water during start up and allowing the steady thermal gradients to develop over sufficient time. This would provide a time history of the temperature experienced at any point along the depth of the well.

The model had to be sufficiently detailed to capture not only the global gradient, but also the local gradients that would enable the assessment of the operational conditions to which the malfunctioning equipment was subjected to. The top graphic shows the extent of the modelling, starting with the outer formation model seen as a light red shade that is sufficiently extended to ensure local boundary effects are far removed. Further, we can see the cement/casing interface and the wellbore, shown with a light blue shade. Within the wellbore we find the injection string, showing two packers, tubing and the control lines – the lines on the bottom of the piping. The control lines are included because they influence the local gradient and because they can be a source of heat.

The result for one of the cases run is shown in the dynamic temperature distribution graph at the bottom. Note how the starting point is the geothermal gradient, getting warmer with depth. As water flows down the well during start up, the temperature changes and is affected by local geometry. Ultimately a steady condition is reached.

This information was provided to the client, who went on to review the malfunction of the equipment with their supplier.