Locating Buried Legacy Wells for Carbon Capture & Storage

On Tuesday 10th December, 2024 it was announced that the Net Zero Teesside Power (NZT Power) and the Northern Endurance Partnership (NEP) CCS project reached financial close, meaning this is set to become a world first project where a fossil-fueled power station will store it's CO2 safely below the seabed in a disused gas reservoir.

But where are these buried well heads, and what condition are they in?

Geophysical Survey Techniques

Survey Pass 1: Magnetics

The XY position of the well head is likely off by a few tens of meters given inaccuracies in positioning and charting when these wells were drilled and abandoned, many of which have been left there since the 1960's and early 1970's. A towed magnetic survey is the most cost effective method of updating the XY position. Towing a passive magnetic system several hundred meters slant range from the vessels USBL isn't going to give you absolute positions, but it's certainly enough to support the next stage of abandoned well assessment surveys, a high-resolution 3D Acoustic survey.

Survey Pass 2: 3D Acoustics

Next stage is to assess exact XY and Z location in addition to conditional assessment. For this we turn to the use of Kraken Robotics' Acoustic Corer (https://www.krakenrobotics.com/our-services/acoustic-coring/).

The Acoustic Corer (AC) provides a 14m wide, >30m deep 3D acoustic volume below the seabed. Given the system is static on the seabed, USBL positioning is more accurate and can be further improved upon by using LBL arrays, providing the most accurate subsea position of a buried well head available.

Equipped with a high, low and parametric chirp projector, the system images in 3D below the seabed, mapping changes in acoustic impedance IE changes from one lithology to another, discrete anomalies such as buried boulders, or, in this case, man made infrastructure in the form of vertical well heads. The seabed context is of particular importance when it comes to identifying the actual wellhead over, say, items of metallic debris surrounding the well, caused by explosive cutting. So, the ability to identify a discrete anomaly over a continuous structure is an important factor to consider.

Centered on the updated magnetic position, the survey design will provide three AC scans, each capturing the well position in a Triple Venn pattern.

By imaging the well in three separate scans, the AC confirms sub-seabed position, removes any acoustic blanking caused by the asset, provides 360° acoustic imagery and, once merged into a seamless 3D volume, increases the signal to noise ratio of the data set making interpretation and data review much clearer.

Positions of infrastructure mapped, the acoustic data can also perform a final integrity check of well heads and pipelines, by locating any leaking hydrocarbons into the sediment or water column. For infield pipelines which are typically buried <5m below the seabed, Krakens Sub-Bottom Imager is typically used, mobilized to an ROV, but for deeper-buried assets and well heads, the AC provides the increased penetration needed.

The AC data is transferred to the vessel live, meaning the buried well head can be plotted whilst the AC is stationary on the seabed and the exact position logged. Once the wellhead position is known sub seabed, a marker is placed on top, enabling future excavation and reentry works to be conducted accurately, referenced to the acoustic survey data results.

Having supported CCS and decommissioning works globally, but also within the UKCS, Kraken Robotics can apply their market-leading 3D acoustic survey services to de risk your projects, get in touch.

Thanks very much for reading, reach out to learn more,

Chris

https://www.krakenrobotics.com/