Downthrown Traps of the Nw Witch Ground Graben, Uk North Sea

Abstract

The structures drilled to‐date in the NW Witch Ground Graben area have been assigned to two broad categories: (i) Upthrown traps with four‐way dip closure or tilted fault blocks, generally located on the franks of the graben: and (ii) Downthrown traps with closure against a major fault, located downthrown on the main graben border fault systems. Many of the downthrown traps are in fact combination traps, having upthrown fault‐seal and/or stratigraphic elements. A study of trap settings in the NW Witch Ground Graben has led to the following conclusions: 1. The success rate for encountering hydrocarbons in upthrown traps and downthrown traps is very similar. 2. The common belief that the footwall seal is the most critical element of a downthrown trap is questionable. 3. Modern seismic data reveals that a high proponion of unsuccessful exploratory wells were not located on a closed structure. The proportion is similar for upthrown and downthrown trap targets alike. 4. There is a lesser chance of the reservoir being absent, or there being no migration route to the trap, in downthrown structures, compared with upthrown ones. 5. Carboniferous sediments can be a footwall seal for a downthrown trap in one location, and a reservoir for hydrocarbons in another. 6. The structural evolution of the NW Witch Ground Graben, within a framework of three intersecting fault trends, has been ideal for the development of downthrown traps. The distribution of a hydrocarbon source rock, the timing of hydrocarbon migration into these structures, and the suitable distribution of sealing strata adjacent to the border fault of the structure, have also been critical.

The origin and distribution of crude oil in Zhu III sub-basin, Pearl River Mouth Basin, China

“…A C C E P T E D ACCEPTED MANUSCRIPT (Dembicki and Anderson, 1989;Hindle, 1989Hindle, , 1997Catalan et al, 1992;Thomas and Clouse, 1995), and structural morphology is the most important factor that controls the positions of petroleum migration pathways in sedimentary basins (Pratsch, 1983(Pratsch, , 1986(Pratsch, , 1994Hindle, 1997).…”

Tectono-stratigraphic development of the southern part of UKCS Quadrant 15 (eastern Witch Ground Graben): implications for the Mesozoic–Tertiary evolution of the Central North Sea Basin

“…A further unconformity separates these units from overlying Oxfordian (J52) sands. Prospectivity in this area is enhanced by the widespread development of a significant reservoir unit, the early Upper Jurassic Piper Sands (sensu lato), which essentially pre-date the development of structural traps in the Jurassic-Lower Cretaceous (Hindle 1989). Syn-tectonic sand units are also important where developed (e.g.…”

Petroleum migration and accumulation in the Bozhong sub-basin, Bohai Bay basin, China: Significance of preferential petroleum migration pathways (PPMP) for the formation of large oilfields in lacustrine fault basins

“…The ''restrainingforce school'' considers the migration pathway as a sheetlike migrating petroleum front (Rhea et al, 1994), and believes that the positions of petroleum migration pathways are largely controlled by permeability heterogeneity of the carrier beds (e.g., Rhea et al, 1994;Bekele et al, 1999Bekele et al, , 2002 and are therefore difficult to effectively predict because of complications with characterizing permeability heterogeneity related to the extent of fracture permeability and permeability alteration due to diagenesis (Bekele et al, 2002). By contrast, the ''driving-force school'' views petroleum migration pathways as very restricted rivers or streams (Gussow, 1954(Gussow, , 1968Dembicki and Anderson, 1989;Catalan et al, 1992;Thomas and Clouse, 1995; Hindle, 1989Hindle, , 1997, and believes that the positions of petroleum migration pathways in sedimentary basins are controlled largely by structural morphology (Gussow, 1968;Momper, 1978;Momper and Williams, 1984;Pratsch, 1983Pratsch, , 1986Pratsch, , 1988Pratsch, , 1994Hindle, 1997), and believes that modeling of petroleum migration pathways can be a powerful tool to reduce exploration risk (Sylta, 1991;Hermans et al, 1992;Hindle, 1997Hindle, , 1999.…”