A well intervention can be a significant cost during a well's lifetime because it entails lost production, caliper surveys, rigging up expensive workover equipment and possesses HSE risks. These high costs impact the operations of mature fields, especially during market downturns. To address the cost effectiveness of well workover activities, an integrated strategy was developed utilising corrosion, erosion and tubing stress analyses. The approach aims to defer unnecessary well interventions and efficiently control budgets using prioritisation of integrity-related well operations.
The proposed holistic workflow for integrity management is based upon the application of well modelling, corrosion, erosion and tubing stress analyses. These elements utilise industry-standard equations and principles to evaluate the potential for integrity loss. The corrosion analyses are based upon the corrected de Waard Milliams correlation, measured corrosion rates and the application of equations of state and thermodynamics to calculate hydrogen sulphide partitioning if sour conditions are prevalent.
Well performance modelling is linked with corrosion analyses where factors such as production rate forecasts, flow velocities, water alkalinity, tubing profile and PVT data are considered. Erosion is an important factor that impacts metallurgy longevity. To calculate erosion rates along production tubing, erosion analyses are supported and correlated with empirical data specific to individual pipe geometry and the metal behavior when contacted by particles in specific flow regimes. Stress analyses calculates various tubing safety factors (burst, collapse, axial and triaxial) to assess the time, mechanism and risk of tubing failure using production rate forecasts, wall thickness and metal loss results obtained from corrosion and erosion analyses.
Because of the complexity of corrosion, corrosion prediction models can significantly over-estimate corrosion rates by several orders of magnitude. Tuning prediction models to caliper data accounts for field-specific factors, e.g. hydrocarbon properties and scale deposition, significantly improve the accuracy of subsequent predictions and increase confidence in well-integrity-review results.
This workflow enables operators to control and balance capital (CAPEX) and operational expenditure (OPEX) related to completions and maintenance by enabling them to more accurately predict failures, plan work-over operations and assess the most cost-effective strategy.