| Popis: |
The seismo-stratigraphy of two Cretaceous carbonate plat-forms was compared. Distinct seismic facies packages, with diagnostic geometries, reflect differing accommodation space evolution, depositional environments and reservoir architecture. These are used to guide static reservoir models and ultimately assist in field development planning. The E-member of the Natih Formation of Oman represents parts of two, 3rd order sequences with a regional unconformity near the top. Seismic facies reflect changes in accommodation space and water energy. Parallel to sub-parallel loopsets at the base and top of the Natih E represent the transgressive phases of the sequences. Combinations of seismic geometries with mounded, clinoforming and planar loopsets in the Middle Natih-E represent highstand complexes. These probably developed over palaeo-topographic highs. Abrupt lateral truncations of parallel reflectors near the top of the Natih-E (E1-E2) are caused by incised channels - probably formed during lowstands near the end of Natih-E deposition. Reservoir is best developed in the mounded seismic facies, followed by the incised channel facies and finally the by the planar facies. The Cogollo Group, Venezuela is divided into - from bottom to top - the Apon, Lisure and Maraca Formations. The Apon Formation, a thick, upward cleaning, transgressive to highstand system, forms complex loopsets with variable character. Planar seismic facies, diagnostic of laterally continuous grainstone sheets, are developed in areas with less accommodation space. Mounded and onlapping seismic facies occur across a regional hinge line. These delineate depositional bodies that probably developed in deeper water. The Lisure Formation comprises interbedded shale and limestone deposited in a low energy environment. These form a planar continuous loopset. The Maraca Formation forms part of a 3rd order transgressive system tract. It is the thinnest unit, but hosts the largest proportion of hydrocarbons. It forms a laterally continuous high-energy grainstone sheet, manifested as a continuous, single loop. Subtle changes in the loop reflect variations in reservoir quality. |
