oil and gas

Question 1

describe the conditions required for the formation of oil and gas (3)

Answer 1

• low oxygen (anaerobic) conditions to prevent decay
• accumulation of marine plankton
• burial with increasing temperature and pressure

Question 1

explain the importance of a source rock, reservoir rock, and cap rock in the formation of an oil trap (4)

Answer 1

• source rock: generating hydrocarbons
• reservoir rock: being porous and permeable to store hydrocarbons
• cap rock: being impermeable to trap hydrocarbons and prevent escape
• all 3 working together to form an effective trap

Question 2

outline how hydrocarbons migrate from source rock to reservoir rock (3)

Answer 2

• primary migration: from source rock into adjacent rock layers
• secondary migration: through porous rocks toward the trap
• movement driven by buoyancy/density differences with water

Question 3

describe the types of traps that can accumulate oil and gas (4)

Answer 3

• antiform trap
• fault trap, oil trapped against impermeable fault surface
• salt dome trap
• unconformity trap

Question 4

explain how porosity and permeability affect the potential of a rock to act as a reservoir (3)

Answer 4

• porosity: the measure of pore space in the rock
• permeability: the connectivity of those pores for fluid flow
• high porosity and permeability being essential for effective reservoirs

Question 5

describe how seismic surveys are used in oil and gas exploration (4)

Answer 5

• sending shock waves into the ground
• measuring the reflected waves with geophones
• interpreting time and strength of reflections to infer rock structures
• identifying traps and possible reservoirs

Question 6

what evidence might indicate the presence of an oil or gas reservoir in a rock core sample (3)

Answer 6

• presence of oil staining/hydrocarbon odour
• high porosity and permeability
• fluorescence under UV light

Question 7

discuss how oil and gas are formed from organic material over geological time (4)

Answer 7

• low oxygen (anaerobic) conditions to prevent decay
• accumulation of marine plankton/organic-rich sediments
• burial with increasing temperature and pressure
• the process taking millions of years under specific geothermal conditions

Question 8

explain why oil and gas exploration often targets sedimentary basins (3)

Answer 8

• thick accumulations of sediment with organic material
• favourable burial and thermal conditions
• likelihood of traps and structural features being present

Question 9

compare conventional and unconventional oil and gas reservoirs (4)

Answer 9

• conventional: oil/gas found in porous, permeable reservoirs
• unconventional: oil/gas found in low-permeability rocks like shale
• unconventional methods needing fracking or horizontal drilling
• economic challenges of unconventional resources