Land surface uplift above compacting overconsolidated reservoirs

An investigation on land surface deformation resulting from the compaction of producing overconsolidated gas/oil reservoirs is presented. If the deple ted formation is significantly less compressible than the surrounding mediu m the vertical reservoir shrinkage is relatively smaller than the horizonta l one, thus generating a possible swelling of the overburden and a conseque nt pronounced decrease of land subsidence or even a surface uplift. Such an effect may also cause an additional land settlement during the post-produc tive recovery phase over fields which exhibit a stiffer behavior in expansi on. In the present paper the surface displacements caused by the depletion of an overconsolidated disk-shaped reservoir are analyzed by a finite eleme nt model taking into account the influence of the disk burial depth and are al extent, the Poisson ratio of the medium, and the underburden stiffness. The results obtained with a more realistic three-dimensional setting are al so discussed to address the possible effects of an irregular reservoir geom etry. (C) 2001 Elsevier Science Ltd. All rights reserved.