Case Study: Four Stratified Annular Fill Layers Identified to Optimize Cut-and-Pull Operation, Offshore Norway

PowerFlex annular evaluation service’s flexural attenuation measurement pinpoints top of cement, solid sag, and casing position to guide efficient casing retrieval

Challenge: Evaluate top of cement, annular fill, and casing centralization to inform planning for retrieval of 9 5/8-in casing.

Solution: Log with PowerFlex annular barrier evaluation service to investigate across the annulus for identifying annular content and imaging the position of the
9 5/8-in casing relative to the 13 3/8-in outer casing string.

Result: Optimized the cut point for operational efficiency on the basis of accurate identification of the casing position and four different sections of annular fill—oil-base fluid, water-base fluid, barite solid sag, and cement—as confirmed by visual casing inspection.

Unknown annular fill

An operator on the Norwegian Continental Shelf (NCS) wanted to improve the efficiency of the cut-and-pull decision for casing retrieval. On average, 35 rig days are required to permanently plug and abandon (P&A) a single NCS well. A significant portion of that operational time is related to casing retrieval because conventional sonic logging is not sufficiently sensitive to subtle changes in the properties of the annular fill over time, especially where fluids and solids are segregated or sag has occurred. The presence of sag increases the pulling force required during casing retrieval, and in many cases forces the casing recovery to be conducted in numerous small sections. Conditions were not favorable for determining casing centralization with conventional acoustic logging, which is adversely affected by the impedance of heavy muds in relation to that of the casing and is also challenged by large casing sizes.

Comprehensive radial measurement of the annulus and casings

The powerful, innovative transducer incorporated in PowerFlex annular barrier evaluation service provides full azimuthal coverage for definitively resolving annular information in casing diameters up to 16 in and thicknesses up to 1 in. Unlike conventional ultrasonic methods, measurements by PowerFlex service overcome attenuation challenges to quantify acoustic impedance for almost any cement type and well fluid, including very heavy muds, and accurately image beyond the primary casing. The superior-quality ultrasonic and flexural attenuation data are available faster through optimized downhole and surface telemetry systems. Enhanced wellsite processing delivers a turnaround time of 2 hours or less from acquisition to receipt of the field answer product.

Quantification of annular fill and casing placement for optimized cut point

Analysis of the third-interface echoes (TIEs) obtained by PowerFlex service across the annulus clearly identified the top of cement, four distinct sections of annular fill—oil-base fluid, water-base fluid, barite solid sag, and cement—and the casing centralization. This combination of reliable information enabled the operator to select the best depth for cutting the casing without experiencing the numerous operational iterations typically required for NCS wells.

Download: Four Stratified Annular Fill Layers Identified to Optimize Cut-and-Pull Operation, Offshore Norway (3.46 MB PDF)

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