Flow experiments were performed on a ten-inch diameter by fifteen-inch longthick-walled cylindrical sample of poorly consolidated sandstone, with a1.25-inch diameter borehole.The purpose was to evaluate the effect ofchanging stress regimes on near-wellbore permeability and liner loading.Aone-inch diameter screened liner was installed in the wellbore to preclude sandproduction.The liner was instrumented with strain gages, in order todetermine stresses resulting from borehole deformation duringproduction.The cylindrical sample was instrumented with pore pressureprobes, placed at different distances from the wellbore, in order to assessvariation in formation permeability with evolving effective confining stressesand production regimes.The major conclusions of this experiment are asfollows:
1. If sand ablation does not occur and if an adequate annular space existsbetween the liner and the wellbore, load transfer to the liner is mitigated. Ifsand ablates and fills the annular gap, the complexity of the load transfermechanism increases dramatically.This has been addressed elsewhere(Abou-Sayed et al., 1995; Willson and Abou-Sayed, 1998).
2. Apparent dilatant behavior in the near-wellbore region leads topermeability increase.
3. An intermediate interval experiences a reduction in permeability, due tostress transfer, following yielding of the inner zone, adjacent to thewellbore.
In unconsolidated formations, it has been speculated that wellbore failuremay significantly increase permeability in the failed zone.This couldalso partially reduce stress transfer to a liner, decreasing the potential forcollapse.However, under these conditions, near-wellbore stresses aretransferred to an intermediate region away from the wellbore wall.Thisresults in reduced permeability in that intermediate region. Controlledwellbore deformation/failure is required to establish an optimum condition thatwould lead to overall skin reduction and reduced liner stresses. It may befeasible to manipulate wellbore deformation by "regulating" the annular spacebetween the wellbore wall and the liner (or by using a deformable liner).
Number of Pages
Looking for more?
Some of the OnePetro partner societies have developed subject- specific wikis that may help.