Abstract
Assuring integrity of offshore well Conductor is one of the challenges in the aged giant offshore fields operating with 1500+ wells. Such fields should have a robust and efficient integrity management system for inspection and assessment of well conductors through the well life cycle. Offshore well Conductors form the secondary load-bearing element in a well, primary being the surface casing. A practical approach in assessing the structural integrity of the well conductor is proposed in this paper.
Wells were classifying into five subgroups; optimized Inspection and Integrity Assessment methods used to establish the structural integrity of conductors; which were evaluated and validated by a 3rd part consultant. The assessment results indicate how over-conservative assumptions in engineering assessment may mislead operators to categorize wells into higher risk. Assessment was performed utilizing various modeling software. Reliability based approach was adopted to accommodate uncertainties in data utilizing appropriate engineering judgement to tackle data gaps. Average thickness measured at discrete elevations was compared with the calculated minimum required thickness (MRT) to assess the structural integrity status of conductors. This approach helped in the decision making and planning for risk mitigation repairs.
The results of optimized inspection techniques and structural assessment methodology lead to establishment of clear pattern for critical well conductors and applied to the groups to decide on maintenance strategy. The conductor wall thickness data measured from automated thickness measurement technique is matching with the measured data from manual thickness measurements. The average wall thickness at each elevation, obtained from the raw automated thickness measurement technique data to be used for assessment of the conductor. After building good confidence in the mode of failure the results indicated that manual thickness measurement technique is sufficient to assess the structural integrity of the conductors.
The consultant has performed parametric studies to validate the Minimum Required Thickness (MRT) for the most onerous well in the group; by modelling the boundary conditions of conductor span between the guides, the critical water depth, well depth etc. Sensitivity studies were performed considering the environmental loading due to wind, wave, current; vortex induced vibrations, cement height behind the pipes etc. From the new findings the integrity status of the current wells risk ranking will be reviewed and if the average measured thickness is greater than the MRT then a repair program is no more required. The resource utilization was optimized based on the final outcome of the exercise.
A procedure based optimized inspection techniques and structural integrity assessments to the group the well conductors resulted in the revision of risk ranking of wells, efficient maintenance planning and achieve high-cost optimization for its life extension. The outcome of the consultancy study will also substantiate our current method of conductor assessment and decision for repair based on risk-based approach. Based on the learnings this paper will be focusing on utilizing optimal inspection and assessment approach.
Simple and cost-effective thickness measurement terahertz system based on a compact 155 μm λ/4 phase-shifted dual-mode laser
