麻豆传媒

The predominantly lacustrine Albert Formation (late Devonian to possibly earliest Visean) consists mainly of grey sandstones and shales and contains oil, gas, albertite, oil shale and salt. Our present level of understanding of the Albert oil shales has been obtained largely from cores. Conventional core-logging techniques recognize oil shale units on a scale of metres. Bulk samples are commonly taken at regular 1.0-1.5m intervals and analyzed for their mineralogy and oil yield. This approach does not consider the variability of the oil shales (commonly on the order of 5-10cm).

Detailed logging of three cores (Petro-Canada Dover No`s 1 and 2, Can. Oxy. Albert Mines No. 5) and examination of physical properties (colour, lamination specific gravity, grainsize, sedimentary structures, composition) of core samples indicate 11 distinct lithotypes. Organic-poor lithotypes are breccia, sandstone, massive siltstone, laminated siltstone and massive mudstone. Organic-rich lithotypes are laminated mudstone, dolostone, oil shales A, B and C and massive oil shale. Markov Chain analysis of Albert strata from two of the cores indicates that the lithotypes exhibit patterns of vertical sequence. Transitions commonly occur between organic-rich lithotypes which are developed within the sequence as follows: laminated mudstone - oil shale C - oil shale B - oil shale A. Dolostone and massive oil shale are transitional with oil shale C and sandstone or siltstone (massive and laminated) respectively and are rarely developed. Technical analyses (mineralogy, geochemistry, organic petrology and organic geochemistry) of organic-rich lithotypes shows that the transition from laminated mudstone to oil shale A corresponds to an increasing organic carbon (specifically lamalginite) and carbonate content and decreasing silicate content:

Laminated Mudstone (Uneconomic). Very coarsely laminated with organic - inorganic couplets averaging 1.96mm, medium dark grey - light olive grey - pale yellowish brown, with fish and plant fragments, pyrite, siderite nodules and sedimentary fills common. Mudstone intraclasts present locally. Illite, dolomite and albite predominate; total organic carbon (TOC) averages 1.13% with liptodetrinite and minor lamalginite. Specific gravity averages 2.79.

Dolostone (Uneconomic). Very coarsely laminated with couples of dolomite-rich and silicate-rich laminate averaging 1.54mm, alternating pale yellowish brown and brownish black, with fish fragments and pyrite common. Dolomite predominates, TOC averages 1.92% with liptodetrinite and minor lamalginite. Specific gravity averages 2.69.

Oil Shale C (Marginal; uneconomic to low grade). Coarsely laminated with organic - inorganic couplets averaging 0.73mm, light olive grey - plate yellowish brown, with fish fragments and pyrite common. Illite, dolomite and albite predominate, TOC averages 2.86% with equal proportions of lamalginite and liptodetrinite. Specific gravity averages 2.77.

Oil Shale B (Low to medium grade). Finely laminated with organic - inorganic couplets averaging 0.49mm, pale - dark yellowish brown, with fish fragments, loop-bedding and pyrite common. Illite, dolomite and calcite predominate, TOC averages 15.7% with lamalginite and minor liptodetrinite. Specific gravity averages 2.18.

Massive Oil Shale (Medium grade). Massive with organic matter finely dispersed throughout, dark yellowish brown, with fish fragments and pyrite common. Illite, calcite and dolomite predominate, TOC averages 7.26% with liptodetrinite and minor telalginite and lamalginite. Specific gravity averages 2.38.

The transition from breccia or sandstone to oil shale A is inferred to reflect nearshore to offshore deposition in a slightly saline and alkaline lacustrine environment. Nearshore settings were characterized by "shallow" waters with high energy conditions and clastic input. Offshore settings were characterized by "deep" waters and low energy conditions which favoured algal growth and carbonate production.

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