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The subsidence occurring in the Ekofisk field originates from the compaction of the reservoir rock due to the increasing stress placed upon it as reservoir pressure is reduced with production from the field. The mechanical properties of the reservoir rock determine how much compaction will take place for given conditions in the field and are therefore a key factor in determining the degree to which subsidence will occur. These mechanical properties can be combined with other reservoi r informati on (pressure, overburden load, structure, etc.) in simulators to predict the amount of compaction and surface subsidence that will occur in the life of the field. For this to be done accuratel'y, there must be sufficient information to describe the compaction behavior of all the rock within the reservoir for all conditions encountered.

A finite-element computational procedure for simulating the reservoir compaction and subsidence processes at Ekofisk is described. Data inputrequirements are considered, and results are presented for selected reservoir management options. Field measurements of subsidence, subsidence rates, and subsidence-bowl profiles are shown to be in good agreement with calculated results.

No abstract

Mechanical properties have been determined for Ekofisk reservoir rock for use in subsidence simulation. Tests were to describe the mechanical properties of the Ekofisk chalk for reservoir conditions. The mechanisms and time dependence of chalk co, paction and the effect of waterflooding on chalk strength were also examined.