Compaction- and Shear-Induced Well Deformation in Tyra: Geomechanics for Impact on Production

Schutjens, P. M. T. M. (Shell Global Solutions International B.V.) | Fokker, P. (Shell Global Solutions International B.V.) | Rai, B. B. (Shell Global Solutions International B.V.) | Kandpal, J. (Shell Global Solutions International B.V.) | Cid Alfaro, M. V. (Shell Global Solutions International B.V.) | Hummel, N. D. (Shell Global Solutions International B.V.) | Yuan, R. (Shell Global Solutions International B.V.) | Klever, F. (Shell Global Solutions International B.V.) | De Gennaro, S. (Shell Global Solutions International B.V.) | Vaibav, J. (Shell Global Solutions International B.V.) | Bourgeois, F. (Mærsk Oil) | Calvert, M. (Mærsk Oil) | Ditlevsen, F. (Mærsk Oil) | Hendriksen, P. (Mærsk Oil) | Derer, C. (Mærsk Oil) | Richards, G. (Rockfield Software) | Price, J. (Rockfield Software) | Bere, A. (Rockfield Software) | Cain, J. (Rockfield Software)


ABSTRACT: Multi-scale numerical geomechanical models for reservoir and overburden deformation in the Tyra chalk field (Denmark) were made, and calibrated by laboratory deformation tests and field data. The mechanical interaction between the compacting and deforming formation, cement and casing was 1) modeled as a function of well orientation, cement distribution, and mechanical properties, 2) followed by probabilistic analysis of the model results in well-failure risking models to gain insight in the effects of rock deformation on well failure, both in space and time, and then 3) used as input in fluid-flow models to forecast the impact of well-failure on production. The risk analysis revealed that, whilst further Tyra compaction will probably lead to more well failure, its impact on production is probably low. Our geomechanical modeling helped to reduce uncertainty in the high-cost multi-year Tyra Future field upgrade planned for the next years to support Tyra production over the next decades.


1.1 Problem definition

About five meters of maximum subsidence has occurred so far in the Tyra chalk field (Denmark), significantly reducing the gap between wave crest and platform base (see Figures 1a, b). In addition, well deformations in reservoir and overburden have been measured and inferred by caliper data and hold-up-depth incidents (HUD) during logging and work-overs (Figures 1c, d). In the overburden, these have been interpreted mainly from the Upper Lark to Sele-Lista formation, 120 m to 400 m above the top reservoir at about 1950 m TVDss.

With the remaining 35% of the total depletion planned for the next decades, some 8 meters of total subsidence may occur by the end of Tyra field life (about 2042). Also, in view of the increasing reservoir compaction strains, there is concern that wells could catastrophically fail (and thus stop producing, i.e. terminally fail) as a result of the accumulated deformation and/or a possible acceleration of reservoir/overburden deformation. In the framework of the multi-year “Tyra Future” project (in which the Tyra production facilities are adapted to the subsiding sea-bed) field-wide and well-scale finite-element geomechanical models were built to 1) describe the compaction and subsidence, 2) study the mechanical effects of the compacting reservoir and its deforming overburden on cement and casing as function of well inclination, cement distribution, and mechanical properties of formation, cement and casing, and 3) provide input to reservoir fluid-flow simulations to assess the impact of Tyra well failure on production.

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