GATE Petroleum Engineering Oil and Gas Well Testing Syllabus

Oil and Gas Well Testing syllabus — full chapter and topic list

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

1. 1

   Diffusivity Equation, Derivation & Solutions

   1 topic

   • Radius of Investigation
2. 2

   Principle of Superposition

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

3. 3

   Horner’s Approximation

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

4. 4

   Drill Stem Testing

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

5. 5

   Pressure Transient Tests: Drawdown and Build Up-Test Analysis

   1 topic

   • Wellbore Effects
6. 6

   Multilayer Reservoirs

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

7. 7

   Injection Well Testing

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

8. 8

   Multiple Well Testing

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

9. 9

   Interference Testing

   overview

   Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

10. 10

    Pulse Testing

    overview

    Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

11. 11

    Well-Test Analysis by Use of Type Curves

    overview

    Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

12. 12

    Gas Well Testing

    overview

    Examined as a single unit within Oil and Gas Well Testing — no further topic split in the official outline.

Oil and Gas Well Testing flashcards for GATE Petroleum Engineering

19 of 50 cards from the Oil and Gas Well Testing deck — real questions with worked answers.

1. Define the radius of investigation in a well test.

   It is the effective distance from the wellbore that a pressure transient has propagated into the reservoir at a given time, i.e. the radial distance reached by the pressure disturbance caused by changing the flow rate at the well.

2. Write the field-units equation for the radius of investigation $r_{inv}$.

   $$r_{inv} = \sqrt{\frac{kt}{948\,\phi\mu c_t}}$$ with $r_{inv}$ in ft, $k$ in md, $t$ in hours, $\mu$ in cp, and $c_t$ in psi$^{-1}$.

3. How does the radius of investigation scale with flowing time $t$?

   It scales with the square root of time, $r_{inv} \propto \sqrt{t}$, so doubling the radius requires roughly four times the test duration.

4. In the radius-of-investigation formula, how do permeability $k$ and porosity $\phi$ each affect $r_{inv}$?

   $r_{inv}$ increases with permeability ($r_{inv}\propto\sqrt{k}$) and decreases with porosity ($r_{inv}\propto 1/\sqrt{\phi}$); higher $k$ lets the transient travel farther while higher $\phi$ slows its advance.

5. How does total compressibility $c_t$ and viscosity $\mu$ influence the radius of investigation?

   $r_{inv}\propto \dfrac{1}{\sqrt{\mu c_t}}$, so higher viscosity or higher total compressibility both reduce the radius of investigation for a given time.

6. Why is the concept of radius of investigation important when planning a well test?

   It tells how far into the reservoir the test 'sees', so it sets the minimum test duration needed to detect a boundary, fault, or pressure-support feature at a known distance, and defines the volume of reservoir characterized by the test.

7. Give the diffusivity-based proportional form of the radius of investigation.

   $$r_{inv} \approx \sqrt{\frac{\eta t}{C}}, \qquad \eta = \frac{k}{\phi\mu c_t}$$ where $\eta$ is the hydraulic diffusivity and $C$ is a dimensionless constant ($\approx 948$ in field units when stated for $r_{inv}$).

8. What is the hydraulic diffusivity constant $\eta$ and its formula?

   It governs how fast a pressure transient diffuses through the reservoir: $$\eta = \frac{k}{\phi\mu c_t}$$ Larger $\eta$ means faster pressure propagation and a larger radius of investigation.

9. A common rule expresses $r_{inv}$ using the dimensionless time. What is the relationship between $r_{inv}$ and time through $t_D$?

   With $t_D = \dfrac{0.0002637\,k t}{\phi\mu c_t r_w^2}$, the transient reaches $r_{inv}$ when $t_D$ at that radius is about $0.25$ (i.e. $r_{inv}=2\sqrt{0.0002637\,kt/(\phi\mu c_t)}$ leads to the $948$ constant).

10. What is the drainage radius and how does it differ from the radius of investigation?

    The drainage radius $r_e$ is the fixed outer boundary of the region a well ultimately drains under (pseudo)steady state, while the radius of investigation grows with time during the transient period until it reaches the boundaries; once boundaries are felt, $r_{inv}$ stops growing.

11. During infinite-acting radial flow, what assumption about boundaries is implied by the radius-of-investigation concept?

    That no boundary has yet been reached: the pressure transient is still moving outward through an effectively infinite reservoir, so the response is governed only by reservoir/fluid properties and not by any limit.

12. How is the radius of investigation used to estimate the time to reach a known boundary at distance $L$?

    Set $r_{inv}=L$ and solve for time: $$t = \frac{948\,\phi\mu c_t L^{2}}{k}$$ giving the approximate flow time before the boundary's effect appears in the pressure data.

13. Why does the radius of investigation NOT depend on flow rate $q$?

    Because it describes how far the pressure disturbance has travelled (a function of the diffusion of pressure), which depends only on reservoir/fluid diffusivity and time; the rate $q$ controls the magnitude of the pressure change, not the speed of its propagation.

14. For a gas well, which parameter in $r_{inv}$ makes the radius of investigation strongly pressure-dependent?

    Total compressibility $c_t$ (dominated by gas compressibility) and gas viscosity $\mu$ vary strongly with pressure, so $r_{inv}=\sqrt{kt/(948\phi\mu c_t)}$ must use pressure-evaluated (often pseudo-pressure/pseudo-time) values.

15. Define wellbore storage (afterflow).

    It is the effect by which, after the surface rate is changed, the wellbore fluid itself continues to supply or absorb flow (by expansion/compression or changing liquid level) so the sand-face rate differs from the surface rate until the wellbore stabilizes.

16. Write the definition of the wellbore storage coefficient $C$.

    $$C = \frac{\Delta V_{wb}}{\Delta p}$$ the change in volume of wellbore fluid per unit change in wellbore pressure, with units of bbl/psi (field) or m$^3$/Pa (SI).

17. Give the wellbore storage coefficient for a well controlled by fluid compression (single-phase wellbore).

    $$C = V_{wb}\,c_{wb}$$ where $V_{wb}$ is the total wellbore fluid volume and $c_{wb}$ is the compressibility of the wellbore fluid.

18. Give the wellbore storage coefficient for a rising/falling liquid level in the wellbore.

    $$C = \frac{144\,A_{wb}}{5.615\,\rho} = 25.65\,\frac{A_{wb}}{\rho}$$ where $A_{wb}$ is the cross-sectional area of the wellbore (ft$^2$) and $\rho$ is the fluid density (lbm/ft$^3$), giving $C$ in bbl/psi.

19. Define the dimensionless wellbore storage coefficient $C_D$ (field units).

    $$C_D = \frac{0.8936\,C}{\phi\,c_t\,h\,r_w^{2}}$$ where $C$ is in bbl/psi, $h$ in ft, $r_w$ in ft, and $c_t$ in psi$^{-1}$.

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