Diagenetic sequences in low-permeability argillaceous sandstones

Abstract

A regular sequence of mineral paragenesis is observed in low-permeability (‘tight’), very fine-grained sandstones of brackish marine to fresh water origin in portions of the Cretaceous of the Rocky Mountains, North America. From pore throat to pore centre in these rocks, the common authigenic sequence is illite (pore throat), kaolinite, silica (pore centre), and siderite (pore centre but after silica). Associated fine- to medium-grained sandstones exhibit a sequence of quartz followed by kaolinite plus traces of calcite from pore throat to centre. Comparison of Gibbs' free energies of formation calculated by the method of Tardy & Garrels show values decreasing in the same order as paragenesis (illite, kaolinite, silica, siderite) observed in the low permeability very fine-grained sandstones. Diagenetic sequences in the coarser sandstones do not match the order of free energies of formation. This implies that early precipitation in very fine-grained sandstones probably occurs under nearly static conditions, whereas constant fluid throughput in coarser grained rocks leads to a markedly different diagenetic sequence. Thus, two potential sandstone reservoirs, one coarse and one very fine, commonly will have different authigenic mineral suites though their original pore waters were broadly identical.

A review of sandstone illite cements and aspects of their significance to hydrocarbon exploration and development

“…Thomas 1978;Burley 1984;Kantorowicz 1984) given the right geochemical conditions (cf. Hurst and Irwin 1982) but may be of significance in terms of producing large volumes o f illite (cf.…”

“…(1976), and Boles and Franks (1979, or assume illite t o be a direct precipitate (e.g. Thomas 1978;Waugh 197%;Colter and Ebbern 1979;Odom et al 1979;Guven et al 1980;H u n t and Irwin 1982). Several authors (e.g.…”

The Effect of Authigenic Clays on Fault Zone Permeability

“…Authigenic clays are formed by diagenetic alteration of in situ minerals in impure (e.g., arkosic sandstones, lithic arenites) and have been identified in 90% of sandstones (from a study of 785 sandstones, Wilson & Pittman, 1977). Authigenic clays precipitate within pore spaces and, although relatively minor in volume (<10%), they have been shown to significantly decrease pore connectivity and permeability by over five fold (Bjørlykke and Jahren, 1992;De Waal et al, 1988;Howard, 1992;Hurst & Nadeau, 1995;Pallatt et al, 1984;Stalder, 1973;Thomas, 1978;Wilson et al, 2013;Wilson & Pittman, 1977;Worden & Morad, 1999). Mechanisms for permeability reduction due to pore filling clays are: Precipitation of authigenic clays within the pore space which dominantly constrict pore throats (Wilson & Pittman, 1977); complex pore filling morphologies which reduce the effective porosity (porosity that contributes to permeability) by creating microporosity (Nadeau & Hurst, 1991); and porosity reduction due to the formation of water shell on the clay surfaces creating a double electric layer (DEL) and diffuse layer (Derjaguin et al, 1987).…”

Some Applications of Scanning Electron Microscopy to the Study of Reservoir Rock

“…The Upper Cretaceous Almond and Ericson formation sandstones (Mesaverde Group) of southwestern Wyoming provide good examples of the influence of clay minerals on porosity and permeability. SEM study of samples from both reservoirs 13 showed that the clay minerals differed in the two reservoir rocks, both in composition and position, within the pore system. The Almond formation reservoir rock typically contained discrete coarse kaolinite euhedra packed in some pores (Fig.…”