Page 55 - Fundamentals of Gas Shale Reservoirs

Continental slope/ basin Biogenous (siliciclastic) 7 (1–27) II ± sulfur HI = 500 (150–800) 10–130 Supply, slope stability, and bottom currents Resedimentation and contour currents on slope and proximal basin; some midwater suspensions Marine algae, bacterial mats(?) Open marine pelagics and limited benthics Restricted on slope, but widespread in basin

Siliciclastic biogenous HI = 530 (165–825) Water depth, bottom energy, and supply Distal riverine plumes, oceanic currents, storms, and tides; surface, midwater flows, and bottom Marine algae (±some Open marine benthic and pelagic; some fine plant debris; spore abundance provides distance to shoreline Widespread lobes and sheets at highstands

Characteristics of shales and of major shale depositional environments (after Bohacs, 1998, table 1 and Potter et al., 2005, Table 5.1)

Shelf 4.6 (1.1–20) I/II 3–40 currents plants)

Siliciclastic coal HI = 280 (170–520) Diverse depending on type but includes overbank flows, shifting channels, longshore currents, tides, and storms Similar to alluvial except for widespread delta front deposits and some bay fills

Deltaic 6 (3–34) III, III–I 20–200 Ratio of inshore wave/tidal power to supply As in alluvial, but also some brackish marine

Coal siliciclastic HI = 188 (35–599) Longshore currents, tides, and storms; mud deposition behind barriers except for fluid mud along open coastlines invertebrates Limited except for some large lagoons and for open coastlines

Coastal 9.2 (4–17) III, III–II 5–50

Overfilled Siliciclastic coal 7 (0.5–45) I/III HI = 600 (50–700) 10–30 Supply + H 2 O >> accommodation; minor role for climate Oscillating, but prograding shoreline Land plants, algae Modest diversity; plant debris and rare vertebrates Sheets with channel cutouts on prograding shorelines

Lake (600–1100) Supply + H 2 O = accommodation Stable shoreline Great diversity of pelagic and bottom fauna; water depth and permitting Carbonates and black shales widespread
Balanced Biogenous chemical 15 (2–30) I HI = 900 5–15 Mostly wind‐driven, but also flood plumes, storms, turbidity currents (deep lakes), stratification, and Algae (±land plants) climate most

Underfilled Chemical (evaporites) biogenous 1.5 (0.2–15) I HI = 400 (10–600) 1–5 Supply + H 2O << accommodation Very climate sensitive Stable shoreline overturning Algae, bacteria Sparse, restricted fauna (high salinity or deep water) Carbonates, evaporites, and black shales most widespread

Fluvial/ floodplain Siliciclastic 2 (1.8–50) III HI = 150 (230–445) 10–70 Ratio of load to discharge; gradient Overbank flows/shifting channels/ floods; suspension in strongly turbulent, unidirectional flows Land plants, algae Plant debris, spores, pollen, and rare vertebrates and invertebrates Limited by channel cutouts and valley width

TABLE 2.1 Lithology TOC (%) Type of organic matter Typical thickness (m) Major controls Current systems Organic matter input Fossils Lateral continuity