GATE Petroleum Engineering Enhanced Oil Recovery Techniques Syllabus

Enhanced Oil Recovery Techniques syllabus — full chapter and topic list

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

1. 1

   Basic principles and mechanism of EOR

   3 topics

   • Concept of pattern flooding
   • Recovery efficiency
   • Permeability heterogeneity
2. 2

   Screening of EOR process

   2 topics

   • Macroscopic displacement efficiency
   • Microscopic displacement efficiency
3. 3

   EOR methods

   4 topics

   • Chemical flooding
   • Miscible flooding
   • Thermal recoveries
     • Steam stimulation
     • Hot water & steam flooding
     • In-situ combustion
   • Microbial EOR

Enhanced Oil Recovery Techniques flashcards for GATE Petroleum Engineering

24 of 51 cards from the Enhanced Oil Recovery Techniques deck — real questions with worked answers.

1. What is Enhanced Oil Recovery (EOR) and at which production stage does it typically apply?

   EOR (tertiary recovery) is the recovery of oil by injecting materials (gases, chemicals, heat) not normally present in the reservoir to alter fluid/rock properties. It follows primary recovery (natural drive) and secondary recovery (water/immiscible gas injection), targeting the oil left behind ($\approx 60\text{--}70\%$ of OOIP).

2. Define pattern flooding in the context of injection schemes.

   Pattern flooding is the systematic arrangement of injection and production wells in repeated geometric patterns (e.g., five-spot, seven-spot, nine-spot, line drive) so that injected fluid sweeps oil uniformly toward producers. Used where there is no strong natural dip or aquifer drive.

3. In a regular five-spot pattern, what is the ratio of producing wells to injection wells?

   $1:1$. Each injector at the center is surrounded by four producers at the corners of a square, but each corner well is shared among four patterns, so the net producer-to-injector ratio is $1$.

4. What are the producer-to-injector ratios for the normal seven-spot and normal nine-spot patterns?

   Normal seven-spot: producer-to-injector ratio $= 2:1$ (injectors at hexagon centers/corners). Normal nine-spot: producer-to-injector ratio $= 3:1$ (one center injector with corner and side-center producers).

5. What distinguishes a 'normal' (regular) pattern from an 'inverted' pattern?

   In a normal pattern the injection wells are at the corners (more producers than injectors for spots); in an inverted pattern the well roles are swapped so there are more injectors than producers (e.g., inverted nine-spot has injector-to-producer ratio $3:1$). Inverted patterns increase injectivity.

6. Write the overall recovery efficiency $E_R$ as the product of its component efficiencies.

   $$E_R = E_D \cdot E_V = E_D \cdot E_A \cdot E_I$$ where $E_D$ = microscopic (displacement) efficiency, $E_V$ = volumetric sweep efficiency, $E_A$ = areal sweep efficiency, and $E_I$ = vertical (invasion/conformance) efficiency.

7. Give the formula for microscopic displacement efficiency $E_D$ in terms of saturations.

   $$E_D = \frac{S_{oi} - S_{or}}{S_{oi}} = 1 - \frac{S_{or}}{S_{oi}}$$ where $S_{oi}$ is the initial oil saturation in the swept zone and $S_{or}$ is the residual oil saturation.

8. Define macroscopic (volumetric) sweep efficiency $E_V$.

   $E_V$ is the fraction of the total reservoir volume contacted (swept) by the displacing fluid. It combines areal sweep $E_A$ (plan view) and vertical sweep $E_I$ (conformance): $E_V = E_A \cdot E_I$. It reflects how well the displacing fluid contacts the bulk of the reservoir.

9. What reservoir property most strongly governs microscopic displacement efficiency, and which dimensionless number controls it?

   Microscopic efficiency is governed by interfacial/capillary forces. It is controlled by the capillary number $$N_c = \frac{v \mu}{\sigma}$$ where $v$ = velocity, $\mu$ = displacing-fluid viscosity, $\sigma$ = interfacial tension. Increasing $N_c$ (e.g., by lowering $\sigma$) reduces residual oil and raises $E_D$.

10. State the definition of the mobility ratio $M$ and its formula for a waterflood.

    Mobility ratio is the mobility of the displacing fluid divided by that of the displaced fluid: $$M = \frac{\lambda_{displacing}}{\lambda_{displaced}} = \frac{k_{rw}/\mu_w}{k_{ro}/\mu_o}$$ A favorable (stable) displacement has $M \leq 1$.

11. How does mobility ratio $M$ affect areal sweep efficiency?

    A favorable mobility ratio ($M \leq 1$) gives high areal sweep and a stable, piston-like front. An unfavorable ratio ($M > 1$) promotes viscous fingering and early breakthrough, lowering areal sweep $E_A$.

12. Define permeability heterogeneity and name a common quantitative measure of it.

    Permeability heterogeneity is the spatial variation of permeability within a reservoir. A common measure is the Dykstra-Parsons coefficient of permeability variation, $V_{DP}$, derived from a log-probability plot of permeability.

13. Give the Dykstra-Parsons coefficient of permeability variation formula.

    $$V_{DP} = \frac{k_{50} - k_{84.1}}{k_{50}}$$ where $k_{50}$ is the median permeability (50th percentile) and $k_{84.1}$ is the permeability at one standard deviation (84.1 percentile) on a log-normal probability plot. $V_{DP}=0$ is homogeneous; $V_{DP}\to 1$ is highly heterogeneous.

14. What is the Lorenz coefficient and what range does it span?

    The Lorenz coefficient $L$ measures permeability heterogeneity as twice the area between the flow-capacity vs storage-capacity (cumulative $kh$ vs $\phi h$) curve and the $45^\circ$ line of perfect uniformity. It ranges from $L=0$ (homogeneous) to $L=1$ (completely heterogeneous).

15. How does the mobility ratio relate to vertical sweep when layers have contrasting permeability?

    In a layered reservoir the displacing fluid advances faster in high-permeability layers; an unfavorable mobility ratio worsens this channeling, lowering vertical (conformance) sweep $E_I$. A favorable $M$ allows the front in low-perm layers to keep pace, improving vertical sweep.

16. List the three main categories of EOR methods.

    1. Chemical methods (polymer, surfactant, alkaline, ASP, micellar). 2. Miscible/solvent (gas) methods ($\ce{CO2}$, hydrocarbon gas, $\ce{N2}$, flue gas). 3. Thermal methods (steam stimulation, steam/hot-water flooding, in-situ combustion). (Microbial EOR is sometimes listed as a fourth category.)

17. What is the primary objective of polymer flooding, and what property is added to the injected water?

    Polymer flooding adds water-soluble polymer (e.g., partially hydrolyzed polyacrylamide, HPAM, or xanthan biopolymer) to increase the viscosity of injected water. This lowers the mobility ratio $M$, reducing viscous fingering and improving both areal and vertical sweep (macroscopic efficiency).

18. Does polymer flooding mainly improve microscopic or macroscopic displacement efficiency? Explain.

    Mainly macroscopic (volumetric sweep) efficiency. By raising water viscosity it reduces $M$ and improves conformance/areal sweep. It does little to reduce residual oil saturation (microscopic efficiency), since it does not significantly lower interfacial tension.

19. What is the principal mechanism of surfactant (micellar) flooding?

    Surfactants lower the oil-water interfacial tension by 3-4 orders of magnitude (to ultralow $\sigma \approx 10^{-3}\,\text{mN/m}$), greatly increasing the capillary number $N_c$. This mobilizes trapped residual oil and improves microscopic displacement efficiency $E_D$.

20. What does ASP flooding stand for, and what is each component's role?

    ASP = Alkali-Surfactant-Polymer. Alkali generates in-situ surfactant (saponification) and reduces surfactant adsorption; Surfactant lowers interfacial tension to mobilize residual oil; Polymer increases viscosity to improve mobility ratio and sweep. ASP combines microscopic and macroscopic benefits.

21. In alkaline flooding, how is in-situ surfactant produced?

    Injected alkali (e.g., $\ce{NaOH}$, $\ce{Na2CO3}$) reacts with naturally occurring organic acids (naphthenic acids) in acidic crude oils to form soaps (in-situ surfactants) that lower interfacial tension. Hence alkaline flooding works best with high-acid-number crudes.

22. Define miscible flooding and contrast first-contact vs multiple-contact miscibility.

    Miscible flooding injects a solvent that mixes with reservoir oil in all proportions, eliminating the interface (zero interfacial tension) so residual oil $\to 0$. First-contact miscible: solvent and oil mix immediately on contact (e.g., LPG). Multiple-contact (dynamic) miscible: miscibility develops after repeated mass transfer between oil and gas (vaporizing or condensing gas drive).

23. What is the Minimum Miscibility Pressure (MMP)?

    MMP is the lowest reservoir pressure at which a given injection gas becomes (dynamically) miscible with a given crude oil, achieving very high displacement efficiency. The reservoir must be operated at or above MMP for a miscible flood to work.

24. Why is $\ce{CO2}$ a favored miscible flooding agent, and what is its typical MMP range?

    $\ce{CO2}$ achieves miscibility (multiple-contact, vaporizing/condensing) at relatively low pressures, swells the oil, and reduces its viscosity. Typical MMP is about $\sim 1100\text{--}1500\,\text{psi}$ ($\sim 7\text{--}10\,\text{MPa}$), much lower than $\ce{N2}$ or flue gas, making it widely applicable.

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