Some safety considerations when flowing a well for the first time
We would like to share with you some simple safety considerations from a well clean-up, i.e. when flowing the well for the first time. These are some good working practices which will help to reduce the possibility of a dangerous situation occurring. These considerations are very simple but sometimes not followed, perhaps because of high confidence from routine operations and previous successes.
Start flaring during daylight
On some clean-up operations, perforations and initial flaring occurred during the night. Despite some safety culture, some teams may not be willing to wait a couple of hours for day lights or may not see any risk associated with performing one of the most hazardous operations during the hours of darkness.
To be carried out safely, perforating and flowing the well for the first time require good visibility. The essential personnel in the well test area need to be experienced, alert and aware of any hazard. As a result, the start of a well clean-up and initial flow of hydrocarbons to surface should whenever possible coincide with daylight hours. Later on, flow during the night should only be possible if the well has stabilized.
Use of fixed chokes to clean-up a gas or gas condensate well
The adjustable choke is very simple and practical to use, especially during clean-up operations. However, there have been some couple of incidents in the North Sea, when the adjustable choke gets eroded with gas flow during clean-up. Unfortunately, these well test incidents no longer get shared between companies.
The adjustable choke is more likely to get eroded and in this case, the upstream choke pressure decreases while the downstream choke pressure increases. On some occasions, experienced people won’t spot (or understand) the problem, when under pressure. They may then take some actions that may render the situation worse and lose control of the test.
Some acknowledge this problem but hardly take any action for “simplicity” and “practicality” of the adjustable choke. We may wrongly think that it is “designed to get eroded” or that “in case of erosion, we just need to replace the adjustable choke with a new one and voila”.
For gas or gas condensate wells, it is recommended to clean up the well through only fixed chokes on both sides of the choke manifold. This should also apply for high pressure wells.
Slowly open the well during clean-up
On some tests, the well is started at a high choke size and the choke is then quickly increased to maximum size, in less than half-an hour from start-up. Did we say we need to be cautious when bringing hydrocarbon to surface for the first time from an unknown reservoir ?
There may be a need to accelerate the recovery of the liquid cushion and get hydrocarbon at surface to minimize clean-up time and therefore rig time ($). However, this may represent a safety issue. With a high choke setting, we may have less control with liquid recovery and the arrival of gas at surface, with potentially some risk with low pressure tanks and other equipments. We need to take extreme care not to overflow and overpressure the tank. If you want to minimize rig time and flaring, there are other techniques to do this- which are much safer, by using the latest well test analysis tools and techniques.
The choke should be opened on a 4 or 8/64” position, and then slowly increased by 4/64” increments. When opening up the well, monitor both upstream and downstream pressure for erosion or plugging, as mentioned in the Well Clean-up session. The downstream choke pressure shouldn’t be higher than the pressure rating of the downstream low pressure equipments. And the well should be cleaned at maximum choke size. (Don’t wait to connect the well to the production facilities to increase the drawdown in the first week of production).
You can check for the presence of gas in the tubing with the DP across the multiple gauges that are separated by some vertical distances (this assumes access to real-time data with several wireless gauges along the tubing), a change in noise at the choke, some gas bubbles when using the choke hose in a liquid container, etc. You could also use the recovery volume to guide you. As soon as most of the cushion is recovered or that gas is detected at surface, we should bypass the tank.