Leakage Through Top Seals During Reservoir Production

Some drainage of pore fluids in the top seals might occur at the time scale of production due to changes of pore pressure in the reservoir. The resulting compaction may have consequences for the sealing capacities of the cap rock, as it could induce leakage along the well annulus. In order to investigate capillary effects and drainage of intra-reservoir and/or overburden seals, special laboratory tests have been performed in NGI's rock mechanics laboratory. Examples of the depth of influence of the reservoir pressure diffusion (depletion) inside a top seal are given on a field scale. Also the additional compaction due to drainage from the cap rock, under burden and mudstone intervals within the reservoir is investigated on a field scale with a 1D coupled consolidation program. The additional compaction and settlement are found to be significant and this may affect the wells or installations in an unfavorable way (well failure or leakage along wells etc). It is therefore important to characterize not only the hydro-mechanical behavior of the reservoir sediments during production, but also that of the near non-pay sediments.