Question

In an oil trap formed by an anticline, _____________ accumulates on top, ____________ in the middle, and ____________ at the bottom.
A. natural gas, oil, groundwater
B. groundwater, oil, natural gas
C. oil, groundwater, natural gas
D. oil, natural gas, ground water

Answer 1

Hint: Oil and gas traps are below ground traps, also referred to as petroleum traps, where a low-permeability cap rock covers a permeable reservoir rock. This rock combination can take many forms, but they all prevent oil and natural gas from migrating upward through the reservoir rock.

Complete answer:
An anticline is a structural trap shaped into an arch-like shape by the folding of rock strata. Initially, the rock layers were laid horizontally in an anticlinal pit, and then earth motion caused it to fold into an arch-like form called an anticline. This type of structure is noticeable on a seismic segment, but the actual structure can be obscured by velocity changes above the anticline because seismic sections are typically 'time sections'. The structural contours form closed loops in an anticline. In an anticline, the reservoir rock layer must be overlain by fine-grained cap rock that seals the top and sides. The crest height above the lowest structural contour that is closed is the closure of the anticline pit. Therefore, it is the portion or depth of the hydrocarbon that may retain or contain the anticlinal structure. If no hydrocarbon below closes the contour below, it will change by spilling into the next structure. Usually, the structure is filled with oil or gas.

So, with this we can conclude that natural gas accumulates on top, oil in the centre, and groundwater at the bottom in an oil trap created by an anticline.

Hence, the correct answer is option (A).

Additional information:
An anticline 's core and internal layers may serve as reservoirs for different fluids. In particular, anticline formations can be highly predictive of petroleum reservoirs. When the anticline is formed from sedimentary rock layers, this is particularly true. Anticlines form a structural trap that can absorb hydrocarbon pockets in the arch's bend. Impermeable rock beds in the anticline peak trap hydrocarbons, also referred to as seals or cap rock. In the pore spaces of the reservoir rock at the centre of the arch, this allows oil and natural gas to build up. Salty water also fills the lowest sections of the reservoir rock, essentially sealing the hydrocarbons into the arch. The largest oilfields, in general, occur in anticlines containing sedimentary rock.

Note: A number of faults will trim the anticlines. A good linked system may be created by intertwined fractures, inconsistencies, and shallow reservoirs, causing the oil entering the system to become substantially thickened during migration. There are some self-sealing effects on the thickened oil.