Technical Triumphs

The exploration horizons from the Paleogene period are older and have generally been buried deeper than the reservoirs previously developed in the Gulf. Consequently, they tend to have more challenging porosity and permeability characteristics than the younger reservoirs produced in the Gulf of Mexico (GoM).

In addition to the challenging rock properties, the initial reservoir pressure is lower than typically encountered. Shell will use artificial lift through a subsea separation and boosting system to enhance recovery.

Once installed, the Perdido spar will shatter the current spar water depth record by over 2,200 feet. With increased water depth comes additional challenges due to extreme water pressure and cold temperatures and extreme marine conditions, such as wind, waves, currents and seasonal tropical storms.

Accomplishing this record-breaking feat will require cutting-edge technology and engineering. “We couldn’t do this project without technology. Technology enables us to do things we’ve never done before and do those things we have done before more cost effectively,” Project Manager Dale Snyder notes.

Two major technologies are playing a key role in the field’s development

Perdido Direct Vertical Access Spar illustration

This will be the first application of full host scale subsea separating and boosting, which enables improved recovery by removing about 2000 psi of back pressure from the wells.

“Perdido has low-energy reservoirs, with low temperatures and pressure, so we have to separate liquids and gas at the seafloor and then pump it to the surface. Without developing the technology to do this, we simply couldn’t reliably produce the fields,” Snyder says.

It will be the first application of wet tree direct vertical access (DVA) wells from a spar.

Using a DVA configuration allows a larger number of subsea completions to be accessed by the facility’s rig drilling, resulting in significant savings in the drilling and completions programs for these wells.

The wet tree DVA system will use a single high pressure drilling and completion riser suspended from the host to access 22 subsea trees directly below the host. The configuration will allow the use of a surface blow-out preventer (BOP) for the drilling, completion and later sidetracking of wells.

By utilizing a single well slot for accessing the wells beneath the host, the size and cost of the host can be reduced without limiting well count flexibility, which is important given the increasing subsurface challenges in a maturing deepwater environment.

“Basically, the DVA allows us to have a large number of wells needed to develop this field,” Snyder notes.

“With more traditional DVA systems, we would be looking at significantly greater space requirements on the topsides to accommodate the wells system. The advantage of the wet tree DVA is that it reduces the space required and, therefore, the cost impacts from the wells system,” says Rome Gonazlez, Wells team lead.

Incorporation of newly developed procedures for drilling and completing wells with a surface BOP and installing subsea trees will be the key to efficient operations from the fit-for-purpose platform drill rig.