Question 1 of 7: Reservoir Engineering Terminology

Question 1: Reservoir Engineering Terminology (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Find. A brief (one-to-two sentence) engineering definition of each of the ten terms (a)–(j).

Approach. Each term is answered directly from its standard reservoir-engineering/petrophysics definition; no calculation is required.

a) Reservoir rock

A porous and permeable rock (commonly sandstone, limestone, or dolomite) whose interconnected pore network can store and transmit oil, gas, and water in economically producible quantities.

b) Trap

A subsurface configuration — structural (e.g., an anticline or a fault juxtaposing rock against a seal) or stratigraphic (e.g., a facies pinch-out or unconformity) — that is capped by an impermeable seal and halts the upward/lateral migration of hydrocarbons, allowing them to accumulate.

c) Secondary oil migration

The movement of hydrocarbons, after primary migration expels them from the source rock, through permeable carrier beds and fracture networks toward a trap, driven mainly by the buoyancy of oil and gas relative to the denser formation water.

d) Wettability

The tendency of one fluid phase (typically water) to preferentially adhere to and spread over the rock's mineral surface in the presence of an immiscible second phase (typically oil), set by the relative strength of adhesive (fluid–rock) versus cohesive (fluid–fluid) molecular forces.

e) Secondary porosity

Pore space created after original deposition and lithification — by fracturing, dissolution (vugs), or dolomitization — as distinct from the primary, depositional intergranular porosity.

f) Tortuosity

The ratio of the actual, winding length a fluid particle must travel through the pore network to the straight-line (apparent) distance between the same two points; it quantifies how convoluted the flow paths are and always exceeds 1.

g) Contact angle

The angle, measured through the denser (usually water) phase, at which the oil–water interface meets the solid rock surface; it is the direct measure of wettability preference (<90° water-wet, >90° oil-wet).

h) Residual oil saturation

The fraction of pore volume still occupied by oil after a displacing fluid (water or gas) has swept through a zone as thoroughly as it can under the prevailing forces; below this saturation the oil is disconnected and immobile regardless of further flooding.

i) Overburden pressure

The total vertical stress at a given depth caused by the weight of the overlying rock, fluid, and sediment column; it is shared between the rock matrix (effective/grain stress) and the pore-fluid pressure.

j) Effective permeability

The rock's ability to conduct one particular fluid phase (e.g., oil) through its pore network when more than one immiscible phase is present at a given saturation; it is always less than or equal to the absolute (single-phase) permeability.