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.
TÜV Rheinland Sonovation operates the D / C PEC technology to be able to measure accurately the remaining wall thickness of the surface casing, intermediate casing and the conductor at the splash zone level. D / C PEC is an application for offshore wells, using pulsed eddy currents. The inspection can be executed during production of the offshore well.
The corrosion is unpredictable and concentrates mainly around the splash zone between the highest (HAT) and lowest astronomical (LAT) tide but can also be present at the top side and other locations of the well. The D / C PEC probe will be inserted in the annulus between the conductor and the surface casing (D-PEC) or in the annulus between the surface casing and intermediate casing (C-PEC) to make the measurements.
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. Corrosion of the surface casing happens in both cemented and noncemented offshore wells.
TÜV Rheinland Sonovation has a total well integrity concept available, which contains; -D & C PEC, -Modern CAD/FEM tools, -Corrosion and chemistry analysis, global well safety analysis. A full corrosion monitoring program with D & C PEC is high value information for gaining advanced knowledge of the integrity of the offshore well to enable better planning of production and well-abandoning activities.
In close partnership with one of the oil majors in Europe, TÜV Rheinland Sonovation developed a total approach to determine the integrity of offshore wells. The approach consists of the following activities:
Wellhead “gap” measurements
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.
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.
D & C PEC wall thickness measurements
PEC stands for “Pulsed Eddy Current” and measures the wall thickness by magnetizing the surface of the object under assessment. This technique does not require the surface to be cleaned.
D-PEC: 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. 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.
C-PEC: For the C-PEC measurements, the annulus between the surface casing and the intermediate casing will be entered with or without a lubricator via a valve on the well head. The C-PEC equipment is intrinsically safe.The casing is measured between LAT and direct under the christmas tree in 20-cm increments and up to every 50 cm in less critical zones.
Fluid water samples
Water samples can be taken and investigated in a laboratory to check the condition of the water and rapeseed oil in the annulus.
Well integrity calculations
The management of well integrity is a combination of technical, operational and organizational processes to ensure a well’s integrity during the operating life cycle.
Analyses of fatigue damage due to regional loads and new boundary conditions (long period of operation, bigger blowout preventer, vessels, etc.).
Load case calculation will be performed together with fracture mechanical break-before-leakage analysis.
Wellhead fatigue can occur because of loads due to;
- motion of the platform,
- wave load (regional issues),
- movement from Blowout-Preventer.
Especially on low and high pressure casing, surface casing and welds of all casings, fatigue can occur.
3D numerical simulation and visualization tools for realistic evaluation of material behavior under external loading, together with 3D numerical computation for realistic assessment of external loading, leads to a reliable prediction of damage accumulation, development of recommendations for further safe operation.
Based on data from several validation exercises carried out on pipes, an accuracy of ±5 % (2-standard deviation) is expected for PEC wall thickness measurements on surface casings and conductors.
Benefits at a Glance
- Extend the life of offshore wells.
- Pro-actively and easily check casing corrosion without interrupting production, also if your well is cemented!
- Gain advanced knowledge of well integrity to enable better planning of production and well-abandoning activities.
- Considerably reduce health, safety and environmental risks.
Exclusive D & C PEC Offshore Well Inspection
D & C PEC is an exclusive, patented, non-destructive method used to help you ensure the structural integrity of offshore wells. TÜV Rheinland Sonovation is the only company offering this critical inspection to the market offshore wells.