GATE Petroleum Engineering Petroleum Exploration Syllabus

Petroleum Exploration syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Petroleum Exploration in GATE Petroleum Engineering, not a summary of it.

1. 1

   Classification and Description of Common Rocks

   2 topics

   • Clastic Reservoir Rocks
   • Nonclastic Reservoir Rocks
2. 2

   Origin, Migration, and Accumulation of Petroleum

   overview

   Examined as a single unit within Petroleum Exploration — no further topic split in the official outline.

3. 3

   Petroleum Exploration Methods

   overview

   Examined as a single unit within Petroleum Exploration — no further topic split in the official outline.

Petroleum Exploration flashcards for GATE Petroleum Engineering

22 of 50 cards from the Petroleum Exploration deck — real questions with worked answers.

1. What is a petroleum reservoir rock?

   A rock with sufficient porosity to store hydrocarbons and sufficient permeability to allow them to flow through it under reservoir conditions, enabling economic production.

2. How are reservoir rocks broadly classified by origin?

   Into clastic (detrital/siliciclastic) rocks formed from transported fragments of pre-existing rocks, and nonclastic (chemical/biochemical) rocks such as carbonates and evaporites formed by precipitation or organic activity.

3. Define clastic reservoir rocks.

   Sedimentary rocks composed of fragments (clasts) of pre-existing rocks and minerals that were weathered, transported, deposited, and lithified — chiefly sandstones, siltstones, and conglomerates.

4. What are the most common clastic reservoir rocks?

   Sandstones, which account for roughly half of the world's hydrocarbon reservoirs, followed by conglomerates and fractured siltstones/shales.

5. Define porosity ($\phi$) of a reservoir rock and give its formula.

   Porosity is the fraction of bulk rock volume occupied by pore space: $$\phi = \frac{V_{p}}{V_{b}} = \frac{V_{b}-V_{s}}{V_{b}}$$ where $V_{p}$ is pore volume, $V_{b}$ bulk volume, and $V_{s}$ grain (solid) volume.

6. Distinguish absolute (total) porosity from effective porosity.

   Absolute porosity counts all pore space (connected and isolated), whereas effective porosity counts only interconnected pores available to fluid flow. For reservoir evaluation, effective porosity is used: $\phi_{eff} \leq \phi_{total}$.

7. How does porosity differ between clastic and carbonate reservoirs in character?

   Clastic (sandstone) porosity is mainly intergranular (primary) and fairly predictable; carbonate porosity is highly variable and often secondary (vuggy, moldic, fracture, intercrystalline) due to diagenesis and dissolution.

8. State the theoretical porosity of an ideal rhombohedral packing of equal spheres.

   About $25.95\%$ (commonly stated as $\approx 26\%$), the minimum porosity for uniform spheres; cubic packing of equal spheres gives the maximum of $\approx 47.6\%$.

9. Why is porosity of well-sorted sand independent of grain size for ideal spheres?

   Because porosity for a given packing geometry of uniform spheres depends only on the packing arrangement, not on the absolute diameter — scaling all grains equally leaves the void fraction unchanged.

10. Define permeability and give Darcy's law for linear horizontal flow.

    Permeability $k$ is a rock's capacity to transmit fluid. Darcy's law: $$q = \frac{k\,A}{\mu}\frac{dp}{dx}$$ where $q$ is flow rate, $A$ area, $\mu$ fluid viscosity, and $\frac{dp}{dx}$ pressure gradient.

11. What is the SI and oilfield unit of permeability, and how do they relate?

    The practical unit is the darcy (D); $1\ \text{D} \approx 0.987 \times 10^{-12}\ \text{m}^{2}$. Reservoir permeabilities are usually quoted in millidarcies (mD), where $1\ \text{D} = 1000\ \text{mD}$.

12. Define one darcy of permeability.

    A rock has a permeability of $1$ darcy if a fluid of viscosity $1\ \text{cP}$ flows at $1\ \text{cm}^{3}/\text{s}$ through a $1\ \text{cm}^{2}$ cross-section under a pressure gradient of $1\ \text{atm/cm}$.

13. Distinguish absolute, effective, and relative permeability.

    Absolute permeability is measured with a single saturating fluid; effective permeability is to one fluid in the presence of others; relative permeability is the ratio: $k_{r} = \dfrac{k_{eff}}{k_{abs}}$, with $0 \leq k_{r} \leq 1$.

14. How does grain sorting affect porosity and permeability in clastic rocks?

    Well-sorted sands have high porosity and permeability; poorly sorted sands have smaller grains filling pore throats, reducing both porosity and (especially) permeability.

15. How does grain size affect permeability for similar sorting?

    Coarser-grained sands have larger pore throats and therefore higher permeability; permeability scales roughly with the square of grain (pore) diameter, while porosity is largely insensitive to grain size.

16. What is the textural classification of a clastic rock based on?

    Grain size (gravel/sand/silt/clay), sorting, rounding/sphericity (roundness), and grain-to-matrix relationships — collectively the rock's texture and fabric.

17. Give the Wentworth size boundaries for sand.

    Sand ranges from $\frac{1}{16}\ \text{mm}$ ($0.0625\ \text{mm}$) up to $2\ \text{mm}$. Below sand is silt ($\frac{1}{256}$–$\frac{1}{16}\ \text{mm}$) and clay; above sand is gravel ($>2\ \text{mm}$).

18. What three main components make up a sandstone in the textural-maturity sense?

    Framework grains (sand-sized detrital particles), matrix (fine silt/clay between grains), and cement (chemically precipitated material binding grains).

19. What are the three poles of the QFL (Dott/Folk) sandstone classification?

    Q = quartz, F = feldspar, and L = lithic (rock) fragments. Their relative proportions define quartz arenites, arkoses, and litharenites.

20. Define a quartz arenite.

    A texturally and mineralogically mature sandstone containing more than $95\%$ quartz framework grains with little matrix, indicating extensive weathering, transport, and recycling.

21. Define an arkose.

    A feldspar-rich sandstone containing more than $25\%$ feldspar, typically derived from rapid erosion of granitic/gneissic source rocks with limited chemical weathering.

22. Define a greywacke (wacke).

    A poorly sorted, matrix-rich (>$15\%$ clay-silt matrix) sandstone with abundant lithic fragments, typically deposited rapidly by turbidity currents; generally a poorer reservoir due to high matrix.

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