Origin and evolution of formation waters, Alberta Basin, Western Canada sedimentary Basin. I. Chemistry

Abstract

Inorganic chemical analyses and short-chain aliphatic acid content are used to interpret the origin and compositional evolution of formation waters in the Alberta portion of the Western Canada Sedimentary Basin. Forty-three formation water samples were obtained covering a stratigraphic interval from Devonian to Cretaceous. The data show that: (1) there is a subaerially evaporated brine component that shows no apparent contribution of waters derived from evaporite dissolution; and (2) formation waters have maintained characteristics indicative of subaerially evaporated waters, despite subsequent flushing by gravity-driven meteoric waters in the basin. Formation waters are predominantly Na-CI brines that contain 4-235 g/1 total dissolved solids (TDS). Short-chain aliphatic acids (SCA) range up to 932 mg/l, with the following abundance: acetate >> propionate > butyrate. Their number varies randomly with subsurface temperature, depth, geological age and salinity. Instead, SCA distributions appear related to proximity to Jurassic and Mississippian source rocks and to zones of active bacterial SO4 reduction. Based on chemical composition, the formation waters can be divided into three groups. Group I waters arc from dominantly carbonate reservoirs and Group II from elastics. Groups 1 and II are differentiated from Group II1 in that they are composed of a brine end member, formed by evaporation of sea water beyond the point of halite saturation, that has been subsequently diluted 50-80% by a meteoric water end member. Group III waters are from elastic reservoirs and are dilute, meteoric waters that are decoupled from the more saline, stratigraphically lower, waters of Groups I and II. Group I waters have been influenced by clay mineral transformations in shales surrounding the carbonate reservoirs, ankeritization reactions of reservoir dolomites and calcites, and possible decarboxylation reactions. Group II waters indicate significant leaching reactions, particularly of feldspar and clay minerals. Group I and Group I1 waters both indicate ion exchange reactions were also possible. The waters are near equilibrium with respect to quartz, calcite, dolomite and barite, but are undcrsaturatcd with respect to evaporite minerals (halite, anhydrite). Occurrence of feldspar (predominantly albite) and kaolinite seems to control the population of the water cations. Post-Laramide invasion of meteoric waters provided an impetus for many of the diagenetic reactions in both carbonate, but especially in elastic reservoirs. Subsequent hydrochemical isolation of Group I and I1 waters from further meteoric influences occurred, resulting in pronounced mixing relations and eross-formational fluid flow replacing the once dominant lateral flow.

Fluid inclusion and stable isotope evidence for the origin of mineralizing fluids in south-west England

“…As with high-temperature boiling, evaporation of surface waters leads to the loss of water vapour and consequent isotopic fractionation (Viglino et al, 1985). Large shifts in the original H-and O-isotopic composition of the fluids can occur, to higher 6D and 6~SO values (Knauth and Beeunas, 1986), and Connolly et al (1990) have recently suggested that combined mixing-evaporation processes can lead to large variations in the 6D contents of formation waters. Deep sedimentary basins containing thick accumulations of Permo-Triassic Red Beds and evaporite horizons are present adjacent to the Cornubian Massif (Smith, in press) and, therefore, could have produced such fluids.…”

Isotopic and geochemical characterization of fossil brines of the Cambrian Mt. Simon Sandstone and Ironton–Galesville Formation from the Illinois Basin, USA

“…Brines from Ordovician age and younger strata in the Illinois Basin (i.e., Stueber et al, 1987Stueber et al, , 1993Walter et al, 1990;Walter, 1991, 1994) and brines from Michigan, southwest Arkansas, eastern Ohio, the Alberta Basin and Canadian Shield Lowry et al, 1988;Connolly et al, 1990;Wilson and Long, 1993a,b) have been studied extensively. These studies used various geochemical techniques such as ion concentration ratios, 87 Sr/ 86 Sr, d 18 O, and dD values to understand groundwater evolution including mixing scenarios with evaporitic brines, glacial and non-glacial meteoric waters, signatures of original seawater, the influences of subaerial exposure and evaporation, and water-rock interaction.…”

“…Individual lines: (1) Canadian Shield (Precambrian) fromFrape et al (1984);(2)and(3)Michigan Basin brines (Paleozoic) fromWilson and Long (1993a,b); (4) southwest Arkansas basin (Mesozoic) fromMoldovanyi and Walter (1992); (5) the BFL global regression [Ca excess = 0.967(Na deficit) + 140.3; R = 0.981] fromDavisson and Criss (1996); (6) eastern Ohio basin (Paleozoic) fromLowry et al (1988); and (7) Alberta Basin of Canada (Paleozoic and Mesozoic) fromConnolly et al (1990).…”

Mixing of halite brines with meteoric water in the Clarke Lake gas field, Canada

“…4). CLE is within range of formation waters from the Devonian of west-central Alberta (Connolly et al, 1990;Michael et al, 2003), which these authors interpreted to represent highly evaporated seawater that was variably diluted by meteoric water following the Laramide Orogeny.…”