Transcript Slide 1
Whitings – Source of Black Gold? - UAE Algal mats & lime muds A link to Middle East carbonate source rock potential C.G.St.C. Kendall, Xavier Jenson & Eugene Shinn Departments of Geological Sciences, University of South Carolina, Jackson School of Geology, University of Texas Austin, and Marine Science Center, University of South Florida Outline of Presentation • • • • • • • • The Hypothesis Overview of Arabian Gulf Reserves Geological setting of Arabian Gulf Modern lime mud & cyanobacteria generation of Arabian Gulf Bahamian Whitings Productivity, Sequestration & Organic Matter Geological setting of Arabian Gulf Oil Fields & tie of hydrocarbon sequestered cyanobacterial remains in geologic section Significance of Russian source rock study Conclusions Hypothesis • Significant Holocene accumulations of cyanobacteria & lime mud in Arabian Gulf axis & tidal zones • These sediments have source rock potential • Similar sediments have accumulated since Triassic • Ancient carbonate muds are source of significant petroleum reserves of Arabian Gulf region • The present is the key to the past! Current Middle East Reserves Crude Oil(BB) - Natural Gas (TCF) •Saudi Arabia •Iraq •UAE •Kuwait •Iran •Oman •Yemen •Qatar •Syria •Bahrain •TOTAL 263.5 bbls 204.5 Tcf – 8 Years 112 bbls 109 Tcf 97.8bbls 212 Tcf 96.5 bbls 52.7Tcf 89.7 bbls 812.3Tcf 5.3 bbls 28.4 Tcf 4.0 bbls 16.9 Tcf 3.7 bbls 300.0 Tcf 2.5 bbls 8.5 Tcf 0.1 bbls 3.9 Tcf 675.1 bbls 1,748.2 Tcf MIDDLE EAST FIELDS Location of Middle Eastern Oil Fields Oil Production - Arabian Gulf Productive hydrocarbon section older to West [Paleozoic] & younger at Arabian Gulf Coast [Mesozoic] & youngest in East in Zagros Mts [ Upper Tertiary]. West to East production includes: •Infra-Cambrian Salt •Silurian and Ordovician clastics – Unaizah •Permian clastics & carbonates – Khuff •Upper Jurassic Carbonates - Arab & Tuwaik Mt Grp •Lwr Cretaceous Carbonates – Shuaiba & Thammama •Middle Cretaceous – Mishrif •Tertiary - Asmari Mesozoic through Tertiary-Lime Mud Source Proposed Concept • Arabian Gulf Holocene cyanobacteria & mud accumulations significant in axis & tidal zones • These sediments have source rocks potential • 4000 meters of similar sediments have accumulated here since Triassic • Sequestered ancient carbonate muds are source of the significant petroleum reserves of Arabian Gulf region • The present is the key to the past! Structural Provinces - Arabian Gulf Mesozoic to Tertiary Foreland Basin 4,000 meters of Mesozoic to Tertiary Sediment sequestered NASA Image in Foreland Basin! Analysis of Crude Oils find Alkanes & Isoprenoids • The alkane/acyclic isoprenoid fraction is the main constituent of most crude oils • A large number of crude oils and rock extracts from Timan-Pechora basin (Russia) suggest this fraction is direct product of liquefaction of biological debris preserved essentially unaltered till oil generation. • Result is the primary biological provenance of this fraction is preserved in the oil fraction. Hydrocarbon Source • Collister, Ehrlich, Mango, & Johnson (AAPG, 2004) propose primary organic materials convert to oil as dispersed alkanes & isoprenoids in rocks • Low TOC source or undermature rocks generate significant oil if source carries sufficient special kerogen derived from biological membranes is unchanged till liquefaction • Observations & experiments, mostly French labs, show resistant organic membranes in form of biopolymers play this role. • Stable over a large range of conditions, survive early secondary bacterial attack & late-stage breakdown with increasing thermal stress. Evidence • Significant Holocene accumulations of cyanobacteria & lime mud in Arabian Gulf axis & tidal zones • These sediments have source rocks potential • Similar sediments have accumulated since Triassic • Ancient carbonate muds are source of significant petroleum reserves of Arabian Gulf region • The present is the key to the past! Carbonate Provinces - Arabian Gulf Ramp Open Shelf Basin Restricted Shelf Satellite scenes SW, to West coast of Arabian Gulf 12 July 2006, MODIS Rapid Response system site, Nasa http://rapidfire.sci.gsfc.nasa.gov Dust and Whiting response Weather Station Data Temperatures - pink & MPH windspeed - black. Windspeeds over 25mph coincide with regional "Whiting" blooms. Arabian Gulf Factory producing carbonates & storing products of cyanobacteria since Permian NASA Image A big day for a bloom!! Organics in the Gulf! Nasa Image Whitings common to-day and common back in the Triassic! Organics in the Gulf! Nasa Image Wells and Illling - 1965 • Among 1st to report ” Whitings” offshore from Qatar precipitated in Persian Gulf. • Ascribed whitings to CO2 removal by photosynthesis of phytoplankton. • Groot (1964) lab analysis of suspended sediment offshore was 70% Aragonite, 10% Calcite, 15% Mg Calcite, 5% Quartz & 5% Dolomites. • Lab experiments used NaCO3 to remove CO2 pptated aragonite from Gulf, but rates did not match instantaneous formation of “Whitings” but took 2 to three weeks. NASA satellite scene with very localized & diminished ‘Whitings’ off UAE on Pearl Bank, offshore East Qatar, north flank of Bahrain shoal, and offshore from Saudi/Kuwaiti border Local Whiting Occurrences! PG Gulf Major Source Direct Precipitation Persian Gulf Facies Distribution After Wilkinson & Drummond, 2004 Persian Gulf Mud Distribution After Wilkinson & Drummond, 2004 Lime Mud Sequestered in Basin Axis & Tidal Flats The mud probably forms less than 1% of sediment signal since Mesozoic but forms a formidable source for hydrocarbons of Gulf Facies of UAE Lime muds & organics sequestered in axial trough & tidal flats Axial Muds Skeletal Sands Reefs & Coralgal Sands Ooid Tidal Deltas Coastal Sabkha Cyanobacterial mats Lime mud & organics sequestered in Mangrove swamp tidal flats Shoaling Upward Inner Shelf Cycle Shoaling Up Cycle Abu Dhabi – Mud Flats Abu Dhabi – Mud Flats High Intertidal Cyanobacterial Flats Earlier High Energy Beaches Supratidal Sabkha Evaporites Intertidal Carbonate Flats Tidal Ponds Tidal Pond SURFACE ANHYDRITE POLYGONS HALITE POLYGONS MICROTOME OF CYANOBACTERIAL MATS Modern Sources of lime mud • Isolated seas – Arabian Gulf • Wide platforms in nutrient deserts of tropical seas – Bahamas Bahamian Organic Productivity • Whitings precipitate 1.35 metric tons per year • 25% of Whiting is organic matter – mostly cyanobacteria and microalgae • As much as 1.6% of surface sediment may contain organic matter • Subsurface sediments preserve 1% TOC (up to 4%) • 7Be (half-life 53 days) found in Whitings but absent in resuspended bottom sediment Bahamas Ocean Drilling Transect Kramer, Swart, DeCarlo & Schosvbo, 2005 Modern Sources of lime mud • Isolated seas – Arabian Gulf • Wide platforms in nutrient deserts of tropical seas – Bahamas LIME MUD ACCUMULATES ON BANK, OFF BANK & TIDAL FLATS Aragonite Needles 2.5mm Long & 0.25 mm Wide MAJOR SOURCE OF LIME MUD IN BAHAMAS IS WHITINGS! Sequestration in Downslope wedge Sequestration on Tidal Flat Bahamas – shoals source of mud Rates of Accumulation • Short-lived isotopes determin accumulation rates (Shinn et al., 2000). • Samples analyzed within 20 days of collection using high-resolution gamma ray spectrometer for shortlived isotopes Be-7 & Th-234 with respective half lives of approx. 53 & 23 days. • Active billowing Whitings had Be-7 & Th 234 but bottom sediment depleted. • None of bottom sediment stirred by storms contained short-lived isotopes. • Radiogenic elements adsorbed on sediment surface, or if epitaxial growth occurred, these short-lived isotopes would be present. Bahamian Whitings Instant Precipitates • Whitings vivid white while water outside them is clear! • Instantaneous chemical &/or biochemical aragonite precipitates. • Many Whitings drift back & forth with tides over time continually raining sediment to bottom with no documented dispersal or end. • Wane in intensity at slack tide to strengthen when tide reverses. • Cloud (1961) followed a single Whiting for 48 hours while Shinn et al. (1989) followed Whitings for 24 hrs. • Some persisted for 24 hrs over hard pellet sands with no mud stirred into suspension. Shinn et al. (1989) returned to same Whitings still drifting over pellet sand 2 days later & Robbins et al. (1997) documented persistence from satellite images. • Artificial Whitings of stirred up bottom settled within 6 hours • Nearby natural Whitings persisted and did not dissipate • Whiting water pumped to settling tanks aboard boat settled in 6 hrs. Whiting Mud Sequestration • Hurricanes & winter storms export vast quantities of lime mud over bank edge. • 7 weeks after Hurricane Andrew (1992), lime mud collected as layers up to 5 cm thick over shallow ooid sands near bank edge (Shinn et al., 1993). Layers from slurries of lime mud exiting bank to Florida Straits & Tongue of Ocean. • An up to 90m thick wedge of Holocene sediment at base of Bahama Bank slope (Wilber et al.,1990) represents 40 to 80% by volume of mud presently sequestered for entire bank. • Vertical and lateral progradation rate of wedge is 11-15 m/ka and 80-110 m/ka, respectively (Wilber et al., 1990). Measures amount accumulated during last 68 ka and does not consider Whiting mud carried northward in Gulf Stream to distant locations and/or to dissolution. • Ball et al. (1967) and Perkins and Enos (1968) report significant off-bank sediment transport in Florida following Hurricanes Donna and Betsy. Similar observations made and photographed in Florida by Shinn following Hurricane Andrew in 1992. • Lime mud-laden sediment continues to spill off the platform for weeks following a hurricane. The Bahamian Bank has been submerged for the past 68 ka and is affected by a hurricane every 6 to 10 years. Overproduction, possibly far greater than 280%, is necessary to account for what is presently on the bank. Organic Matter • Phytoplankton nucleae are cores to cells • Viable phytoplankton cyanobacterial cells in Whitings not observed in bottom sediment - deteriorate quickly after deposition (Robbins and Blackwelder, 1992) . • Aragonite needles adher to surface of living planktonic cyanobacteria indicates rapid precipitation within water column (Robbins & Blackwelder, 1992; Yates & Robbins, 1998; 1999; 2001). • 25% of the 1.3 million metric tons ppted & suspended each year in Bahamas is organic matter, dropping to 1.8% of surface sediment. . • Bahamian Bank Whitings & associated organic matter cover more limited areas swept off bank into deep water. Cores through Neogene western platform slope sediments preserve 1% TOC up to 4% (Kramer, Swart. Bahamas Morphology Rim Restricted Shelf Basin Open Shelf Carbonate Mud Settings • Carbonate muds common through earth history • Carbonates signaled by thick sections adjacent to margins of recently pulled apart continental plates &/or in compressional terrains of colliding margins • Carbonate muds collect in: – Lower portions of updip shallow water cycles – Lower portions of downdip restricted basins & basin slopes Organic matter <1% weight of Holocene tidal flats & axial trough ! Carbonate Mud Accumulation Sites of Ancient Arabian • Late Paleozoic to Early Mesozoic behind Structural & Depositional Barriers • Punctuated by limited access to sea & repeated arid climatic events favoring cyanobacterial preservation • Now trapped beneath Arabian Gulf Hydrocarbon Source, Seal, Reservoir • Source Rocks – Permian Khuff - Saudi Arabia – Lw Jurassic Tuwaiq Mt. Group - Saudi Arabia – Lw Cretaceous Maudud Fm. of UAE • Seals – Usually with playa and sabkha evaporites • Reservoirs – – – – – Deep Ghawar Berri, Ghawar Zakum Field, UAE Thamama I, II, and III, Shaybah Mishrif Asmari Arabian Gulf Basin Traces complex history of plate tectonic & sedimentary fill: •Pre Cambrian to Infra-Cambrian - Continental interior •Silurian and Ordovician clastics – Continental interior •Permian clastics & carbonates – Trailing margin •Upper Jurassic carbonates – Trailing margin •Lower Cretaceous carbonates – Trailing margin •Middle Cretaceous – Compression & Zagros Mts initiated •Tertiary carbonates & clastics - Compressional margin Evolution of Arabian Gulf Foreland Basin Compression & Foreland Basin Extensional margin Extensional margin Interior Sag After Kingston et al, 1983 Hydrocarbon Production in Arabian plate Stratigraphic section Section represents approx 2,438.5m in 200 my Accumulation Rate 1.22 mm per 1 Ky Lime Source PERMIAN KHUFF FM DEPOSITIONAL SETTNG (Al-Jallal, 1995) Restricted Entrance To Sea Permian Khuff Saudi Arabia Oman & UAE Structural & Depositional Barrier over Hercynian Horst Blocks Arid Tropics Air System Wide Shadow from Adjacent Continents % WORLD’S SOURCE ROCKS Carbonate Mud Source Rocks After Baum, & Kendall Geological Setting of Jurassic Oil Seal Seal Reservoir Reservoir Intrashelf Basin Intrashelf Basin Lime Source GOTNIAN DEPOSITIONAL SETTING (Al-Sharhan & Kendall, 1986) Lime Source Restricted Entrance To Sea Upper Jurassic Saudi Arabia Kuwait, Iran & UAE Depositional Barrier over Hercynian Horst Blocks Tropical Air System ! Wide Shadow from Adjacent Continents After Dennis Tassa Zagros Fold Mountains - Iran NASA Image Lower Cretaceous Stratigraphic cross-section of Cretaceous Eastern Arabia (Alsharhan & Nairn 1986) Tertiary Lime Source Stratigraphic cross-section of Neogene Arabian Gulf (Alsharhan & Nairn 1986) From International Petroleum Encyclopedia Lime Source ORGANIC MATTER HYPOTHESIS • The Arabian Gulf a sink of organic matter since Triassic • As with modern Gulf much of this organic matter related to multiple organic blooms through geological time • Organic matter trapped in intertidal flat & basinal muds • Dispersed organic matter in form of biological membranes, have simple chemical composition & structure, & so liquefy at a threshold temperature & do not require time & temperature history for maturation. • A burst of oil generation produces transient overpressures resulting in liberation of oil by microfracturing and longrange migration through the resulting fractures. • This ensures that large volumes of oil could be generated over a short time. CONCLUSIONS • Arabian Gulf Holocene cyanobacteria & mud accumulations significant in axis & tidal zones • These sediments have source rocks potential • Similar sediments accumulated since Triassic • These ancient carbonate muds are source of the significant petroleum reserves of Arabian Gulf region • The present is the key to the past! Now to lunch! West of Dhabaiya – Mangrove Swamp Holocene tidal flats are sequestering >1% of weight as organic matter! Bahamas Deep water of marginal zone Shallow tidal flats Bahamas Bahamas Mud transported by hurricanes settle in high energy channels Bahamas – Shoals are a source of mud! Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Bahamas – shoals source of mud Appalachians Ordovician Isolated Foreland Basin Appalachians Ordovician Appalachians - Ordovician Appalachians - Ordovician Appalachians - Ordovician Appalachians - Ordovician Appalachians - Ordovician Appalachians Ordovician Appalachians - Ordovician Appalachians - Ordovician deepening up from grains to mud Appalachians Ordovician Appalachians Ordovician Murray Basin Murray Basin Lime muds & organics sequestered in axial trough & tidal flats Pellets & Grapestones Skeletal Sands Ooid Tidal Deltas Reefs & Coralgal Sands Coastal Sabkha Cyanobacterial mats Cyanobacterial mats Lime mud & organics sequestered in Mangrove swamp tidal flats Intertidal Sand & Mud Flats Tidal Channels Cyanobacterial Mats Sabkha Geologic Cross-Section - Arabian Gulf Gas Paleozoic Stratigraphic Column Arabia Gas Lime Source