Over the past years, the offshore industry has faced a new phenomenon of damage to wells. The surface casing, on which the Xmas tree relies for support, is collapsing due to corrosion. As the number of incidents increases, reactive measures of mobilizing local response teams are no longer appropriate.
Shell Global Solutions developed D-PEC technology in order to accurately measure the corrosion of the surface casing and the conductor. Invisible from the outside, corrosion concentrates around the splash zone between the highest (HAT) and lowest astronomical (LAT) tide as well as at the topside of the well. Corrosion in cemented wells often occurs in the area close to the Xmas tree.
It is impossible to determine corrosion levels from the age of the well and there is no correlation between corrosion in the conductor and the surface casing. A full corrosion monitoring program with D-PEC is highly recommended to both properly inspect and control your valuable assets as well as to help you determine whether to abandon a well.
As the only company offering D-PEC well inspection, TÜV Rheinland can help you to:
Please feel free to contact us at TÜV Rheinland to learn more about how our D-PEC well inspection services can benefit your company.
TÜV Rheinland Sonovation has developed a full approach to determine the integrity of both cemented and non-cemented offshore wells.
The total approach requires the following steps:
1. Wellhead “gap” measurement
To determine that the well is not moving, pictures are taken of the wellhead and a standardized measurement is made. Providing continuous information, a monitoring program can track changes in certain values in order that appropriate action can be taken.
2. Camera inspection
To document and report abnormalities such as eccentric casing and missing centralizers, the annulus between the conductor and the surface casing is inspected with a camera to the fluid level. A video copy of this inspection is delivered as part of the report. The camera is also used to check for obstacles preventing entry with the D-PEC probe.
3. D-PEC wall thickness measurements
PEC stands for “Pulsed Eddy Current” (Link to: Home > Business Customers > Materials Testing and Inspection > Advanced NDT > Pulsed Eddy Current (PEC)) and measures the wall thickness by magnetizing the surface of the object under assessment. This technique does not require that the surface be cleaned. In order to access the annulus between the conductor and the surface casing, a hole can be drilled in the conductor without compromising its strength. A 4” hole is required for lateral access and a 2” hole is large enough for topside access.
An object is measured between LAT and HAT in 20-cm increments and up to every 50 cm in less critical zones. The standard approach starts with the measurement of one particular wind direction. If corrosion is found, the scope of inspection may be expanded to include other wind directions.
4. Fluid water samples
Water samples are taken and investigated a laboratory to check the condition of the water and rapeseed oil in the annulus.
5. Well integrity calculations
Comprehensive inspection results and D-PEC measurements allow the integrity of your well to be calculated and remedial actions to be planned well in advance. If needed, these calculations can be extended to your offshore structure.
Having acquired PEC technology from Shell Global Solutions, TÜV Rheinland Sonovation is now making D-PEC inspection available to the entire offshore industry.
The D-PEC method can be used to determine the range at which wells are affected by corrosion. Corrosion on offshore well-pipe surface casings is usually found at the splash zone area and close to the X-mas tree. The inspection is executed via the annulus between the conductor and the surface casing. D-PEC inspection services based on pulsed eddy-current inspection technology enable you to monitor corrosion of the surface casing and conductor without interrupting production.
D-PEC is an exclusive, non-destructive method used to help you ensure the structural integrity of offshore wells. TÜV Rheinland Sonovation is the only recognized inspection company to currently hold a worldwide license for this particular inspection method.