Ultra-Deep Sub-Salt Hydrocarbon Exploration Targets: Dead Sea Rift Zone-Implications From Ultra-Deep U.S. Gulf Of Mexico, Anadarko, Permian, and Tarim (China) Basin Successes
The major increase of daily petroleum production of the United States is attributed to unconventional and conventional petroleum technological advances. The offshore Gulf of Mexico is contributing significantly to the added absolute daily petroleum production numbers. Recently ultra-deep drilling has added significant oil reserves to Shell, Chevron and Total in the Deepwater U.S. Gulf of Mexico. Shell has announced 6 new discoveries in the Norphlet formation, a Jurassic age aeolian dune sand long thought to be only present onshore.In the 1970’s ultra-deep gas( 19000’, 6 km) was produced onshore from the Norphlet and Smackover in Mobile Bay Alabama. The sourcing is believed to be the Smackover formation, an organic rich carbonate which also serves as a reservoir, an oolitic carbonate in the onshore. Offshore deep-water wells have penetrated up to 1400 feet of net pay sands. Wells were drilled to 29000’,9 km. Seismic profiles demonstrate anticlinal folds associated with the Louan salt mobilization. Reservoir studies suggest facies selective. Sandstones demonstrate primary diagenetic calcium carbonate precipitation and cementation supporting the sandstone infrastructure during compaction which later dissolved with the simultaneous dissolution and migration of hydrocarbons. Changes in pH concentrations created the diagenetic conditions. Ultra-deep drilling sub-salt onshore U.S. Gulf of Mexico (25,000'-35,000', 10 km) has discovered the occurrence of viable petroleum reservoirs at depth with significant methane gas from Cretaceous (Tuscaloosa) and Paleogene age rocks. Mc MoRan Oil &Gas LLC drilled the Highlander prospect inland of the Louisiana Gulf Coast (- 29500’ td.,9 km.). The well encountered 150 feet of net pay, with sandstone porosities of 24 percent and, attained a 75 mmcfg/d on a 42/64th inch choke, with 10300 PSI flowing tubing pressure. The well has produced over 50 BCF of gas since January 2015, and it can be noted that the perforated interval is more than 5000 feet, 1.6 km., deeper than any other producing well in Louisiana. Ultra-deep Gulf of Mexico risked potential may approximate 30 Tcfg. Ultra-deep drilling in the Anadarko basin (30.000’ , 10 km.), and the Permian basin (23.000 ‘. 7 km contain dolostones with porosities of up to 10 percent and are due to mesodiagenetic dolomitization, with onset at 4 km., 12000’, corresponding to a vitrinite reflectance of .55.Xenotopic textures result in the carbonates at ultra-deep depths .Petrophysical studies of the Anadarko basins’s Hutton Group ( lower Paleozoic) demonstrate good reservoir properties with moderate porosities ( 5.2-6.9%) and moderately sized pore throats ( 2.6- 8.8 uM). Higher porosity rocks such containing moldic and vuggy porosity dolostones have lower mercury-recovery efficiencies (RE). The simultaneous reactions of organic and inorganic chemistry creates the ideal sequence of source and reservoir rock timing events. The Paleozoic ultra-deep reservoirs produce primarily gas. The geothermal gradient of the DSR is low (1.14 f/100ft.) Higher geothermal gradients (2.0 f/100ft) exist locally drilled into the salt. The Dead Sea demonstrates extreme subsidence rates (2.66km/my, 8724 ft./my) during the last 1.5 million years, with hydrocarbon generation modelling of the Sedom Deep 1 well suggesting onset at 4 km, 12000 feet. When comparisons are made to basins in North America, Mexico, Cuba, and Bahamas (.20-.50 km/my,656’-1640’/my).the Dead Sea is over 5 times greater in respect to subsidence rates. Hydrocarbon generation modelled in those basins occurred during the Mesozoic. The South Caspian basin demonstrates petroleum systems with drastic subsidence of 10 km.in the past 6 million from the Pliocene and contains a low geothermal gradient (1.20f/100ft). Hydrocarbon basin modelling suggests onset at 10 km,33,000 feet .Thus, the DSR is uncommon with hydrocarbons generated relatively recently in the geologic past. In China, the ultra-deep drilling (7700m, 24000’) resulted in the discovery of giant oil discovery in the Tarim basin. The Paleozoic reservoir contained oil preserved due to a regional low geothermal gradient. The basin underwent rapid subsidence of 2 km in the past 5 million years. Geologists attribute the short duration in reaching its current high temperature to lack of cracking. The departure of thermal maturation organic geochemical relationships due to extreme rapid recent burial may also occur in the DSR where extreme recent subsidence occurred. To the southwest of the DSR, in the Negev, regional studies correlating 18 wells encountered thick Triassic and Jurassic sandstones and carbonates, which are intercalated with marine and non-marine shales. In the Anadarko basin highly porous dolostones at ultra-deep depths are attributed to by shale fluid compaction. Additionally, exposed Upper Cretaceous pinnacle reefs near the western margin of the DSR demonstrate dolomitization, a result of phreatic diagenesis. The USGS estimates, the DSR contains, based on geophysical data, 6km of basin fill with 4 km of pre-basin sedimentary rocks below it. Exploration in the DSR (15 wells) targeted Mesozoic and younger clastics and carbonates in structural traps. The deepest well drilled in the DSR is the Sedom-1 to a depth of 6450 m (21,156’) near the master-faults of the western southern DSR. Seismic profiles suggest the well drilled sub-salt bottomed in Miocene age rocks, basin fill. There exists significant untested potential below the total depth of the Sedom-1 well. Two wells encountered Mesozoic rocks, Aminiz -1 (4605 m. t.d., 15104’) and En Gedi-1 (2949m, t.d., 9072’). Light oil was encountered in two Triassic age dolomites and sandstones. Gas was produced from fields at the graben margins. The sourcing from the hydrocarbon is believed to be the rocks of the Campanian-Maastrictian Menuha and Ghareb Formations, identified as a regionally important source rock from Egypt’s Western Desert to Southeast Turkey. Exploration targets are in the central southern portion of the DSR at a depth of 10 km. (32000’) where the master-transform faults are absent and limited migration of hydrocarbons and salt. Seismic sections demonstrate sedimentary rocks below graben fill. However Syrian Arc anticlines have not been identified in the sub-basin fill Mesozoic rocks. At depth primary reservoirs would be high porosity sandstones and dolostones below the Neogene salt. The trapping mechanisms would be stratigraphic traps diageneticaly controlled.
AAPG Datapages/Search and Discovery Article #90341 ©2019 AAPG Geoscience Technology Workshop, Exploration and Development of Siliciclastic and Carbonate Reservoirs in the Eastern Mediterranean, Tel Aviv, Israel, February 26-27, 2019