Sedimentology and quality of reservoir sandstones within the Carboniferous Frederick Brook Member, Albert Formation, Moncton subbasin, New Brunswick

Abstract

The medial Frederick Brook Member of the Carboniferous Albert Formation is sedimentologically analyzed in this study through the detailed description of approximately 100 m of core from Boudreau-1-98, a borehole located within the Moncton Sub basin of southeastern New Brunswick. Three main lithofacies are identified, these include: (FIA & FIB) penecontemporaneously deformed siltstone and laminated siltstone, respectively; (F2) massive and bedded sandstone; and, (F3) laminated organic rich shales. FIA is interpreted to be a distal lacustrine prodelta deposit, where unstable slopes were present, attributing to the high abundance of penecontemporaneous deformation due to failure on the slopes. FIB represents distal prodelta to deep lacustrine sediment accumulation resulting in the deposition of fine, planar, parallel-laminated siltstones. F2 represents shallower deposition characterize by sand-dominated storm deposits that were possibly remobilized from a distal deltafront environment. F3 represents the deepest deposition within the lake. Four parasequences are defined within the logged section PSI is interpreted to represent a deep lake deposit. This parasequence is composed of FIB and F3, suggesting that sediment supply and hydraulic energy were low. PS2 is interpreted to represent a delta sequence dominated by FIA, FIB and F2, where a general increase in wave and current energy occurs upwards. This is attributed to a decrease in relative lake level. Deposition of PS3 is interpreted to have occurred in a storm-influenced distal prodelta environment. PS3 includes sandy silts deposited from suspension with less abundant, normally graded sand beds that are the result of storm processes. PS4 is subdivided into PS4A, 4B, 4C and 4D. PSA represents a short deepening event as suggested by its overall fining-upward trend. This gradual increase in lake level is followed by three discrete tempestites (PS4B, C & D) that may have local correlative value. Scanning electron microscopy of F2 sandstones was conducted to analyze the porosity and permeability of the potential reservoir sandstones within the Frederick Brook Member. Samples were photographed in backscatter electron mode using carbon coated thin sections, and secondary electron mode using gold coated rock slabs. Sample JB11b and JB9 were taken at depths of -165.5 m and -251.3 m, receptively. These two samples lie above the section logged and were chosen based on their low gamma signature. These are coarser-grained and have noticeable porosity in hand sample. They are both composed of medium- to coarse-grained, F2 sandstones. The last sample, JB4, was taken at a depth of -391 m and is within the logged interval. The reservoir sandstones of the Frederick Brook Member demonstrate varying amounts of porosity and pore interconnectedness due to the presence or absence of carbonate minerals. Each sample demonstrates varying chemical relationships and porosity.