Stress-strain analysis in productive gas/oil reservoirs

✍ Scribed by Gambolati, Giuseppe; Teatini, Pietro; Tomasi, Lucio

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 284 KB
• Volume: 23
• Category: Article
• ISSN: 0363-9061
• DOI: 10.1002/(sici)1096-9853(199911)23:13<1495::aid-nag7>3.0.co;2-7

✦ Synopsis

A numerical study of the stress}strain distribution in a thin disc-shaped reservoir embedded in a poro-elastic half-space and subject to a unit pore pressure decline is presented. The results are then compared with those of a geometrically equivalent porous cylindrical body which is either free to or prevented from expanding laterally (oedometric analogy). The analysis is based on the linear theory of poro-elasticity solved with the aid of the "nite element method. The strength source is provided by the pressure gradient generated in a small region surrounding the gas/oil "eld where pore pressure dissipates. The in#uence of the burial depth c is also investigated. The results show that the reservoir rock undergoes a vertical compaction which is independent of c and very close to the compaction of the equivalent con"ned cylinder. The con"nement factor is also similar. The horizontal displacement is, however, much larger. Its maximum value occurs at the boundary of the "eld and is of the same order of magnitude as . In addition, at the outer reservoir margin shear stresses develop which are totally missing in both the free and the constrained cylinders. It is shown that the vertical displacements of reservoir top and bottom, as well as the radial ones, are sensitive to c, especially in shallow formations. Finally, the largest shear stress is found to be related to the magnitude of the pressure gradient, i.e. to the radial size of the neighbouring volume where pore pressure vanishes.