A petroleum reservoir rock must allow hydrocarbons to be stored and to flow economically to wells. Which property (or combination) best characterizes a good reservoir: low porosity, high permeability, high porosity, or the combination of high porosity and high permeability?

Introduction / Context:Reservoir engineering hinges on two foundational rock properties: porosity (storage space) and permeability (flow capacity). A productive petroleum reservoir must provide sufficient pore volume to hold fluids and adequate connectivity between pores so oil and gas can move to the wellbore.Given Data / Assumptions:

• Rock types can vary (sandstones, carbonates, fractured formations).
• Hydrocarbon production requires both storage and deliverability.
• Economic rates depend strongly on permeability.

Concept / Approach:Porosity is the fraction of bulk rock volume occupied by voids. Permeability measures the ease with which fluids flow through interconnected pores. High porosity without permeability traps hydrocarbons; high permeability with low porosity yields limited volumes. Optimal reservoirs typically exhibit both properties at favorable levels.Step-by-Step Solution:

Verification / Alternative check:Classic reservoir performance equations (e.g., Darcy’s law for flow; material balance for volumes) implicitly require adequate φ (porosity) and k (permeability) to achieve commercial production rates and reserves.Why Other Options Are Wrong:

Common Pitfalls:Assuming one property compensates fully for the other; in practice, both are needed for a good reservoir.Final Answer:Both high porosity and high permeability