Secondary porosity development during late burial in carbonate reservoirs as a result of mixing and/or cooling of brines

Carbonate reservoirs from different geologic provinces record an important event of porosity enhancement by corrosion (dissolution) in diagenetically late, deep burial conditions. Fluid mixing can be detected in successive cement stages preceding major corrosion by means of coupled fluid inclusion microthermometry and stable isotopic composition (delta(18)C, delta(18)O) of carbonate cements. Major corrosion is preceded by recurrent minor corrosion between successive cement stages. The transport of dissolved carbonate away from the system, as well as arrested diagenesis related to hydrocarbon migration appears essential for porosity preservation. Rock observations demonstrate that cooling postdates main corrosion, and appears to be coeval with oil migration. Relatively low-temperature (90-100 degreesC) fluorite with oil inclusions characterises the stage of cooling. Fluorite (and minor pyrite-marcasite, barite-celestite, dickite and quartz) is found in minor amounts filling porosity formed during major corrosion or replacing carbonate cements and matrix. (C) 2003 Elsevier Science B.V. All rights reserved.