Compaction-Induced Porosity/Permeability Reduction in Sandstone Reservoirs: Data and Model for Elasticity-Dominated Deformation

Abstract

Summary Open literature and new experimental compaction data from five reservoir and 16 outcrop sandstones are used to delineate the near-elastic, inelastic, and failure domains in 3D-stress space for porosity classes of 5 to 15%, 15 to 25%, and 25 to 35%. Applications of this compaction-domain model include the analysis of the extent of the near-elastic domain (where elasticity theory can be used to describe and predict rock deformation), the pore-volume compressibility (Cpp), and the permeability reduction as a function of reservoir stress path. This is illustrated for a well-consolidated sandstone reservoir with an average porosity of approximately 18%. Two aspects of dynamic reservoir modeling in the near-elastic domain are addressed: calculation of Cpp from raw volumetric-compaction data as a function of isotropic total stress change, and the correction of Cpp for a nonhydrostatic reservoir stress path. Open-literature work combined with our experimental data indicates that the compaction-induced permeability reduction of 15 to 25% porosity sandstone in the near-elastic domain depends predominantly on the increase of the effective mean stress, not on the reservoir stress path.

Effective stress law for the permeability of a limestone

“…These experimental results can be explained by the pore diameter changes under the effect of the confining pressure and the pore pressure variations. The shape of the permeability curves and its reduction with the confining pressure increase is similar to the results reported in the literature for porous sedimentary rocks [17,24,26], as well as for crystalline rocks [16,17,19]. As mentioned by David et al [25], the compaction mechanism in crystalline rocks is related to the closure of microcracks, and the pressure sensitivity of permeability decreases with an increase in the confining pressure.…”

“…(23), (25) and (26) in Eq. (18), along with some algebraic re-arrangements, the following expression is obtained for the effective stress coefficient corresponding to the variations of the permeability of the model…”

Unraveling reservoir compaction parameters through the inversion of surface subsidence observations

“…This nonlinearity in subsidence response may be seen as a shift between the start of depletion and the (delayed) start of subsidence [19], or as an increase in subsidence rate with time. This time lag in subsidence response has been observed for several oil and gas fields (e.g., Bachaquero [19][20][21], Tia Juana [19,22], the SNOK field [23], and Wilmington [21,24]). The underlying cause of the time lag has been attributed to mechanisms related to reservoir compaction (such as creep, an intrinsic rate effect, and an elastic-plastic transition, [19]).…”

Geophysical investigation of Obot Ekpo Landslide site, Cross River State, Nigeria

“…The level of compaction can significantly reduce the formation porosity because the fine-grained materials that overlie the shallow Cretaceous strata have been forced into the pore spaces (Schutjens et al, 2004;Berisso et al, 2012;Wang et al, 2012). Thus, it is expected that the influence of grain surface conductivity on the bulk resistivity of the shallow sediments will be negligibly small and therefore, their effects can be neglected.…”