Because of anisotropy and inhomogeneity arising from the presence of non-salt interbeds, constructionandoperationofgasstoragecaverninbeddedsaltdepositsaresingularly challenging. In this paper, physical and mechanical properties of common interlayers in bedded salt deposit are discussed. Large behavioral differences among lithologies (shale, mudstone,anhydrite,anddolomite)exist:anhydritesaregenerallyverystrong, mudstonescanbeveryweak,andbotharecommoninterbedsinbeddedevaporites. Based on analysis and experience, we propose four basic issues that must be addressed to estimate operational pressurelimitsin beddedsalt deposits. These issues are the well- bottom tightness, general cavern tightness, cavern roof stability, and flow control.
Salt deposits can be classified into four types according totheirgeometricdispositionandgeological history:
Sedimentary (bedded) salt with a tabular (undeformed) structure (e.g. Prairie Evaporites, Saskatchewan)with approximately horizontal upper andlowerbounds. A subset of this category isrecrystallizedbutundeformed bedded salt (e.g. Lotsburg Salt, Alberta),
Salt deposits with flexural structures possessing deformation-related internalstructuresuchas folded and opened (flexural fractures) dolomite orshalebands,withanoverallthickness dominated bycompressivetectonics(e,g.salt structures inNewBrunswick,foldedsaltthe western limit of the Appalachian thrust belt)
Diapiric salt emplaced by gravitationally- dominated viscoplastic flow from greater depth, forming salt domes, ridges and salt tongues, all having experiencedgreatdeformationsand possessing clearflowstructuresthathave erased mostoftheoriginallithostratigraphy, and havingexperiencedmassive recrystallization(e.g.salt domes,ridgesand tongues in the Gulf of Mexico or offshore Nova Scotia)
Vein-like structures, generally very small-scale, formed byvariousprocessesassociatedwith precipitation,extrusion, orinternaltectonically controlled salt bodies within rock masses.
For flexural and vein-like deposits, in some circumstances solutionstoragecavernscanbe constructed or miningcantakeplace(New Brunswick). However, we do not deal with these classes of deposits because ofstructuralcomplexity,andweaddressonly storage cavernsinbeddeddepositsofsufficient thickness,appropriatedepth,andreasonable lithostratigraphy. For example, thin strata cannot be used because ofvolumeneedsandcavernaspectratio,very deep caverns are plagued by rapid closure, and sequences with largeshaleanddolomitecontentswillpresent excessive solutioning difficulties.
In bedded salts, excessive or thick non-salt interlayers interspersedinthesolublesequence makeit difficult or impossible to construct a cavern of economic storage volume that is also unequivocally stable under the operatin
