Ferroan calcite cement Hibernia Sandstone

Pyrite occurs both as early and late cement in Hibernia Field. Early pyrite is present in early calcite cement, fossil fragments and siderite nodules. Late pyrite is found in intergranular pores and fractures. The association of pyrite with a porous zone in Hibernia Sandstone and its absence in adjacent ferroan-calcite cemented sandstone suggests that this pyrite formed after the dissolution of the ferroan calcite. 

The history of porosity development at the various reservoir levels in Hibernia Field clearly underscores the role of carbonate cements in delaying irreversible porosity loss in sandstone reservoirs. Early non-ferroan and ferroan calcite cements, precipitated at burial depths shallower than 2000 m, are widespread in oilfields around the world (e.g. Lindquist, 1977 Blatt, 1979 Loucks etal., 1984 Olaussen et a/., 1984 Bjorlykke et a/., 1986 Imam Shaw, 1987 Kantorowicz et al., 1987 Saigal Bjorlykke, 1987 and many others) and are typical as first major cements for a group of cement parageneses (Franks Forester, 1984). Four different sources of this early calcite cement have been considered in the literature (i) carbonate dissolu-... 

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