Core analysis of the Hiram Brook Member of the upper Albert formation. The interpretation of the depositional environment and the determination of reservoir prospectivity.

Abstract

The Carboniferous Hiram Brook Member is the upper most member of the Albert Fm. (Horton Group). This study focuses on core from the Moncton Subbasin of the Maritimes Basin, which is located in Southeastern New Brunswick. A portion of one core (Albert Mines 4), totaling 107 m in length, is presented. Detailed sedimentological data are used to interpret the depositional environment. This data is compared to four other cores to assess lateral continuity of sedimentary facies and reservoir potential of the Hiram Brook Mbr. Three lithofacies are recognized in the sedimentological succession. These lithofacies are subdivided on the basis of various sedimentological criteria. Facies IA (FIA) consists of sandy siltstone and is found throughout the Hiram Brook Member. It generally contains low angle parallel laminae and abundant, pervasive penecontemporaneous soft sediment deformation. Poorly developed palaeosol horizons are present. Diagenetic characteristics include, calcite and oxide cements locally, minor pyrite mineralization on fractures, and the presence of calcite veins. There are no biogenic structures present, however rootlets, and wood fragments are observed. Facies IB (F2B) is composed of sandstone and is commonly interbedded with FIA. This facies is characterized by ripple or cross-laminations with local, crude oil staining. Facies 2A (F2A) is a breccia/conglomerate characterized by sharp contacts with erosive bases, and steep, poorly-defined bedding. Locally derived clasts consist of metasediments, gneisses and granites that range from angular to sub-rounded. These originate from the Proterozoic to middle Devonian basement complex. Bedsets characteristically fine upwards. Facies 2B (F2B) comprises oxidized sandstone and is interbedded with F2A. Physical characteristics include low angle parallel laminae, reduction spots, climbing current ripples, low angle tabular cross beds, and trough cross-beds. Trace fossils include Skolithos, and Taenidium. Facies 3 (F3) is composed of shale and is found locally in the Hiram Brook Mbr. Facies 3 is interbedded with FIA and FIB. It contains pervasive fissile units and is black in colour. Soft sediment deformation features are locally present. No bioturbation was observed, however a disarciculated fish fossil was identified. Analysis of FIA and FIB indicates a dynamic lacustrine environment that sporadically experienced the influence of waves. The overall succession indicates cyclic rising and falling of the relative lake level, attributed to either changes in sediment supply or rate of subsidence. Low angle, thin, parallel laminae reflect rhythmic fluctuations of sediment supply under constant sedimentation. Evidence for event sedimentation include the presence of flame structures and graded bedsets Facies 2 is oxidized and is interpreted to represent a decrease in relative lake level. Large angular clasts indicate a proximal source. Reduced zones indicate contrasting geochemical conditions possibly caused by rapid burial. Bioturbation reflects the pause between event deposits and reflects favourable conditions for colonization of the sediment. Climbing current ripples suggest unidirectional currents and high sedimentation rates. Facies 3 is interpreted to represent deposition in a lacustrine, offshore environment. Evidence includes: abundance of low angle parallel laminae, high organic content, and local pyrite on fracture surfaces. The presence of a fish fossil likely indicates a time of high preservation potential. Rootlets and palaeosol horizons indicate shoaling and emergence.