Bu Attifel (Libya) – This field contains an EUR of 2.59 BBO as a single pool inside a tilted horst-block trap within the Lower Cretaceous Upper Sarir fluvial sandstones which are heterogeneous with variable connectivity. Intense early production caused a rapid pressure decline and formation of a secondary gas cap. High GOR wells had to be shut-in and production fell. Down-flank water injection increased production. Wells were acid stimulated and higher permeability units were selectively shut-in due to water breakthrough. Ultimate recovery factor is 59%.
D35 Field (Malaysia) – Online in 1994, oil is produced by solution-gas and aquifer drive supplemented with gas re-injection. The multi-stacked coastal plain to tide-dominated deltaic sandstones of Miocene age have porosities 13-27% and permeabilities 500-4000 mD. Phased development using >40 horizontal wells had reached 21% STOIIP as of 2019.
Gorm (Denmark) – Located in the Danish Central Graben with an EUR of 409 MMBO. Oil is contained in a domal anticline over a salt diapir within a micritic Danian and Maastrichtian chalk reservoir. Matrix porosities are high (15-45%) but matrix permeabilities are only 1-3 mD and production relies on faults and fractures which connect the chalk layers and increase permeabilities to ~40 mD. Development wells are mostly horizontals drilled in a radial pattern from the crest, with water injection via horizontal wells drilled beneath the OWC. Wells require hydraulic fracturing or acid stimulation. Ultimate recovery factor is 44%.
Mitsue (USA) – Onstream since 1964, the field contains a STOIIP of 822 MMBO in the Middle Devonian Gilwood Sandstone. Light oil (41 °API and 0.6 cP) is trapped in a single pool by depositional pinch-out of fluvio-deltaic sandstones into basinal shales. The reservoir has 140-1000 mD permeability and 5-30% porosity. Recovery was initially by weak aquifer, solution-gas and gas-cap expansion drive, which is greatly improved by peripheral water injection and hydrocarbon miscible flood. With a cumulative of 406 MMBO produced by end-2021, an ultimate recovery factor of 52% is expected.
Santa Agueda (Mexico) – Onstream since 1953, the field has a STOIIP of 386 MMBO and an ultimate recovery factor of 31.8%. Heavy oil (16 °API) has been produced from fractured reefal and shoal limestones of the Albian-Cenomanian El Abra Formation by solution-gas drive. Porosity and permeability average 12% and 60 mD, respectively. Developed with 50 producers on a 140 ac well spacing without secondary or EOR recovery, the field was near depletion by end-2021.
Usa Field (Russia) – (A) Light oil (36 °API, 2.1 cP) is produced from Devonian deltaic and shoreface-shelf sandstones by water injection from the onset in 1973. The Devonian reservoir contains a STOIIP of 1667 MMBO and an EUR of 854 MMBO, giving a recovery factor of 51%. Cumulative recovery to 2010 reached 89% of EUR. (B) Heavy oil (12-18 °API, 710 cP) is produced from Carboniferous-Lower Permian carbonates since 1977, initially under moderate aquifer drive, superseded by a variety of thermal EORs since 1982, including hot water injection, continuous steam injection, cyclic steam stimulation, aided by alkaline and surfactant injection, multi-lateral and horizontal drilling, and reverse SAGD. STOIIP is 4796 MMBO and EUR is 1583 MMBO for a recovery factor of 33%. Cumulative recovery to 2018 was 31% of EUR.