Using sketches, describe how the following types of structural oil traps were formed: 1. Anticline trap 2. Fault trap

1. Anticline trap:
- The first sketch shows a cross-section of a sedimentary basin with layers of rock that have been folded into an anticline shape.
- Over time, as sedimentary layers were deposited, the weight of the overlying rocks caused the layers to fold upwards into a dome-like structure.
- Oil and gas migrated from deeper underground reservoirs and became trapped in the porous rock layers at the crest of the anticline, forming an anticline trap.

2. Fault trap:
- The second sketch shows a cross-section of a sedimentary basin with layers of rock that have been offset by a fault.
- A fault is a fracture in the Earth's crust along which movement has occurred. In this case, the layers of rock on one side of the fault have moved vertically relative to the other side.
- As oil and gas migrated through the porous rock layers, they encountered the fault and were trapped against impermeable rock layers, forming a fault trap.

1. Anticline Trap

- Step 1: Sedimentary layers are deposited horizontally.
- Step 2: The layers are folded into an anticline (upward fold).
- Step 3: Oil and gas migrate upwards through the layers and become trapped at the top of the anticline, where the permeability decreases.

[Image of an anticline trap]

2. Fault Trap

- Step 1: Sedimentary layers are deposited horizontally.
- Step 2: A fault occurs, creating a break in the layers.
- Step 3: Oil and gas migrate upwards along the fault plane and become trapped against an impermeable barrier, such as a shale layer.

[Image of a fault trap]