The geology of Bourque: an underground reef

Reef complexes can contain excellent reservoir rocks due to their porous nature, which enables them to hold a large volume of oil that is easy to extract because of their permeability. Porosity refers to the space (the pores in the rock) taken up by the oil within the rock, like the space between grains of sand, for example. Permeability refers to the quantity of fluid that can flow through a rock to the well, based on how interconnected the pores are.

Reefs are structures that form under the sea, generally by means of corals—marine animals that secrete their own calcareous skeletons. Reefs can become huge, like the Great Barrier Reef of Australia. The reefs at Bourque are made of the calcified skeletons of sponges known as stromatoporoids.

In Gaspésie, the structures identified as reefs are over 2,000 metres below the surface and are more than 410 million years old. The reservoir rock they form is covered by a layer of impermeable rock (cap rock) under which the oil is trapped.

Pétrolia identified what appears to be a reef complex during its exploratory work (65 km2 of 3D seismic surveys). A large volume of hydrocarbons is likely located there. To confirm this hypothesis, Pétrolia plans to drill two conventional wells down to the reefs and check for oil. The Bourque No 1 well will be used to study the composition of the oil. Bourque 2 will target a specific point: the accumulation of stromatoporoids (pinnacle reef).

There are three main parts to an oil system: the source rock, the cap rock and the reservoir rock.

Seismics, Bourque 1

Seismics, Bourque 2

Rock porosity, Bourque