Case Study: Spudcan-Pipeline Interaction at the Maria Field - Challenges of Data Interpretation and Comparison of Predicted and Measured Soil Deformation-Paper

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The Maria Field jack-up installation required the Rowan Gorilla VII to operate close to a subsea production pipeline. Initial analyses raised concern about spudcan punch-through and possible damage to nearby infrastructure, but interpretation of the site data was complicated by pore-pressure sensor desaturation in the CPTs. Using the affected readings directly would have underestimated clay strength. Correcting cone resistance using an assumed pore-pressure ratio produced strength profiles consistent with normally consolidated clay and was supported by borehole and laboratory data.<br /><br />Spudcan penetration was assessed using both closed-form bearing-capacity calculations and large-deformation finite-element (LDFE) analyses. Both indicated that punch-through was possible only under low-estimate soil-strength conditions. The LDFE analyses predicted less potential for rapid penetration, partly because they represented the soil plug trapped beneath the spudcan. In the actual installation, careful preloading resulted in a penetration of just 1.2 m, and punch-through did not occur.<br /><br />LDFE analyses also estimated seabed movements at the pipeline, 13 m from the spudcan edge. Pipeline movement was monitored using two inclinometers. Recorded rotations during installation were minor and consistent with predictions for the actual shallow penetration. Movements during spudcan extraction were also smaller than the modelled worst-case estimates, as the analyses assumed extraction from a much greater depth and did not model the pipeline itself.<br /><br />Overall, the investigation and analyses supported safe jack-up installation and showed the value of combining corrected CPT interpretation, borehole data, numerical modelling, and field monitoring when assessing spudcan–pipeline interaction.

Keywords

Maria Field

Rowan Gorilla VII

jack-up installation

spudcan punch-through

subsea pipeline

CPT pore-pressure desaturation

cone resistance correction

large-deformation finite-element

pipeline movement monitoring

spudcan–pipeline interaction