Efficient subsea completions

4th May 2016

Well testing is performed to determine the economic viability of a well and optimise field development plans. When collecting data, it is key that reservoir boundaries are identified, including the nature of the fluids present, and that reservoir pressure and permeability is evaluated. Crucially, this data helps to conclude the rate at which the well will produce and for how long.

Efficient subsea completions are therefore essential when optimising well performance and cost. Performing a well test flow back / clean-up of subsea development wells will confirm the integrity of your completion installation and validate the cash output / flow characteristics prior to completing the well(s).

At the heart of every well test safety strategy are subsea landing strings. Subsea safety systems minimise risks during well completion. Ideally, subsea safety systems and clean-up packages need to deliver a rapid, reliable response in all well conditions e.g. in water depths >5000ft.

Potential hazards when conducting flow back / clean-up operations back to an offshore vessel include movement and drift, due to inclement weather or positional failure, and the formation of hydrates in deepwater. Therefore, providing a dual well barrier between the reservoir and the environment, the facility to disconnect a landing string, and injection point(s) for hydrates, is paramount.

Expro’s subsea technology was recently applied offshore Australia for a campaign of more than 20 high rate gas production wells. A well testing package, including a mega flow test separator and large-bore electro-hydraulic subsea landing string, allowed maximum flow rate. The package reduced clean-up time, removed drilling mud, debris and completion fluids from the wellbore, whilst providing the rapid shut down and disconnect point when flowing at these high gas rates.

In Angola, a high debris electro-hydraulic subsea landing string with a mono-bore riser system that could be utilised on a subsea christmas tree (VXT) dual bore interface, was deployed in ultra-deepwater for a major operator.

The landing string solution was required to complete, clean-up and suspend wells with hydrocarbons safely and economically, prior to installation of the VXT. The mono-bore system eliminated the need for a dual bore riser and provided a unique solution ideal in batch completion scenarios. This allowed the VXTs to be deployed from alternative vessels and installed at a later date, offering schedule flexibility and cost savings for the client.

The cost of unplanned subsea well intervention work is typically high. For operators, safety and reliability is key in bringing hydrocarbons to the surface. Doing it right first time, via efficient well flow back and clean-up, helps to validate the integrity of your completion. Vital decisions can then be made prior to completing and producing from the well, removing the need for costly future intervention work. 

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