List of top Reservoir Engineering Questions

For a hydrocarbon reservoir, the following parameters are used in the general material balance equation (MBE):

\[ \begin{aligned} N & = \text{Initial (original) oil in place, stb} \\ G & = \text{Initial volume of gas cap, scf} \\ m & = \text{Ratio of initial volume of gas cap to volume of oil initial in place, rb/rb} \\ S_{wi} & = \text{Initial water saturation} \\ S_{oi} & = \text{Initial oil saturation} \\ B_{oi} & = \text{Initial oil formation volume factor, rb/stb} \\ B_{gi} & = \text{Initial gas formation volume factor, rb/scf} \end{aligned} \]

The total pore volume (in rb) of the reservoir is:

Which of the following logging tool(s) underestimate(s) porosity in a gas-bearing formation?

The drainage oil-water capillary pressure data for a core retrieved from a homogeneous isotropic reservoir is listed in the table. The reservoir top is at 4000 ft from the surface and the water-oil contact (WOC) depth is at 4100 ft. \[ \begin{array}{|c|c|} \hline \textbf{Water saturation (\%)} & \textbf{Capillary pressure (psi)} \\ \hline 100.0 & 0.0 \\ \hline 100.0 & 5.5 \\ \hline 99.0 & 5.6 \\ \hline 89.2 & 6.4 \\ \hline 81.8 & 6.9 \\ \hline 44.2 & 11.2 \\ \hline 29.7 & 17.1 \\ \hline 25.1 & 36.0 \\ \hline \end{array} \] Assume the densities of water and oil at reservoir conditions are 1.04 g/cc and 0.84 g/cc, respectively. The acceleration due to gravity is 980 cm/s2. The interfacial tension between oil and water is 35 dynes/cm and the contact angle is 0 degree. The depth of free-water level (FWL) is at ________ ft (rounded off to one decimal place).

The formation resistivity factor \((F)\) is related to the formation porosity \((\phi)\) in a water-bearing carbonate formation by the following correlation: \[ F = 0.9 \phi^{-2} \] where \(\phi\) is in fraction. The resistivity of the invaded zone of the formation obtained by the Microspherically Focused Log (MSFL) is \(4.5 \, \Omega m\), and the resistivity of the mud-filtrate is \(0.05 \, \Omega m\). The formation porosity is ________ % (rounded off to one decimal place).

Which of the following option(s) is/are CORRECT for well testing analysis of a reservoir?
The porosity of a formation with matrix density of \(2.65 \, g/cc\) and fluid density of \(1.0 \, g/cc\) is \(0.15\). The formation has shear modulus of \(30 \, GPa\) and bulk modulus of \(36 \, GPa\). The compressional wave velocity in the formation is \(\underline{\hspace{1cm}} \times 10^3 \, m/s\) (rounded off to two decimal places).

The laboratory analysis data obtained from the core is as follows: - Weight of clean dry core in air = 30 g - Weight of core completely saturated with oil = 32 g - Weight of saturated core completely immersed in oil = 24 g If the density of oil used for saturation of core during the experiment is \(0.88 \, g/cc\), then the effective porosity of the core is  ________ % (rounded off to two decimal places).

The Buckley Leverett frontal advance theory is employed to evaluate the performance of the water flooding operation in a horizontal reservoir. \[ \text{Cross-sectional flow area} = 40000 \, ft^2, \quad \text{Payzone thickness} = 20 \, ft, \quad \phi = 20\%, \quad q_w = 1000 \, rb/day, \quad L = 1000 \, ft, \quad PVWI = 0.5 \] The time of breakthrough is \(\underline{\hspace{1cm}} \) days (rounded off to one decimal place).

A hydraulically fractured vertical well has fracture permeability of \(4000 \, mD\), reservoir permeability of \(80 \, mD\), fracture width of \(0.12 \, in\), and fracture half-length of \(1000 \, ft\). Dimensionless fracture conductivity is \(\underline{\hspace{1cm}} \times 10^{-4}\) (rounded off to one decimal place).
Log-log plot of pressure drop (\(\Delta p\)) versus time (\(t\)) obtained using well test data is matched with one of the Grigarten type curves. Thereafter, a point on the type curve is chosen with \(P_D = 10\) and \(t_D / C_D = 100\). The corresponding match point on the log-log plot is \(\Delta p = 250 \, psi\) and \(t = 10 \, hrs\). Oil flow rate = \(500 \, rb/day\). Viscosity of oil = \(1.5 \, cP\). Thickness of reservoir = 10 ft and formation volume factor of oil is \(1.2 \, rb/stb\). The permeability of the reservoir is \(\underline{\hspace{1cm}} \, mD\) (rounded off to one decimal place).
Correlation equations for gas compressibility factor \((z)\) and viscosity \((\mu)\) as functions of pressure \((p)\) are given: \[ z = C_1 p^{-0.25}, \quad \mu = C_2 p^{1.25} \] where \(C_1 = 1.96\), \(C_2 = 7 \times 10^{-4}\). Pressure \(p\) is in psi, and viscosity \(\mu\) is in cP. Real gas pseudo pressure corresponding to \(p = 2500 \, psi\) is \(\underline{\hspace{2cm}} \times 10^6 \, psi^2/cP\) (rounded off to two decimal places).

An isotropic and homogeneous oil reservoir has porosity \(20\%\), thickness \(20 \, ft\), and total compressibility \(15 \times 10^{-6} \, psi^{-1}\). Variation of flowing bottomhole pressure with time under pseudo-steady state is: \[ p_{wf} = 2850 - 5t \] During the well test, oil flow rate is \(1800 \, rb/day\). The drainage area of the reservoir is \(\underline{\hspace{1cm}} \), \(\mathrm{acres}\) (rounded off to two decimal places).

A homogeneous rock layer Q of density \(2600 \, \text{kg/m}^3\) is lying below homogeneous rock layer P of density \(2400 \, \text{kg/m}^3\).
A compressional wave travels from P to Q. On reaching the interface, this wave is incident normally and gets reflected and refracted.
The velocity of the compressional wave is \(2.7 \, \text{km/s}\) in P and \(3.5 \, \text{km/s}\) in Q.
The ratio of reflection coefficient to transmission coefficient at the interface is:
Match the well logging methods in GROUP I with their corresponding measured parameters in GROUP II. \begin{tabular}{|c|c|} \hline GROUP I & GROUP II
\hline (P) Neutron log & (I) Resistivity in the flushed/invaded zone
(Q) Density log & (II) Hydrogen ion concentration in the formation
(R) Microspherically Focused Log (MSFL) & (III) Interval transit time of a compressional wave
(S) Sonic log & (IV) Electron density of the formation
\hline \end{tabular}
Reservoir Quality Index (RQI) based on Kozeny–Carman equation as a function of permeability (\(k\)) and porosity (\(\phi\)) is given by: \[ RQI = C \, f(k,\phi) \] where \(C = 0.0314\). If permeability \(k = 152 \, \text{mD}\) and porosity \(\phi = 0.18\), then find RQI in \(\mu m\) (rounded off to two decimal places).
The ratio of number of production to injection wells for a regular Seven-Spot pattern is .............. (rounded off to one decimal place).
Consider the diffusivity equation for radial flow of a fluid in an infinite and homogeneous reservoir: \[ \frac{1}{r}\frac{\partial}{\partial r}\left( r \frac{\partial P}{\partial r} \right) = \frac{1}{\eta} \frac{\partial P}{\partial t} \] where \(P\) denotes pressure, \(r\) is the radial distance from the centre of the wellbore, \(t\) denotes time, and \(\eta\) is the diffusivity constant. The initial pressure of the reservoir is \(P_i\). The condition(s) used in the derivation of analytical solution of the above equation for pressure transient analysis in an infinite acting reservoir is/are:
Which of the following statement(s) is/are CORRECT about polymer flooding?
Which ONE of the following rocks shows the highest reading in the natural gamma ray log?
\(C_1, C_2,\) and \(C_3\) are the Dietz shape factors of three reservoirs with circular, square, and rectangular drainage areas, respectively. The well is located at the geometric center of the reservoir. Which ONE of the following options is CORRECT about the shape factors?
Four curves designated as I, II, III, and IV are shown in the figure. \(q_f\) is the bottomhole oil flow rate, \(q_s\) is the surface oil flow rate, and \(B_o\) is the oil formation volume factor. Which ONE of the following curves depicts the minimum wellbore storage effect? \begin{center} \includegraphics[width=0.7\textwidth]{04.jpeg} \end{center}
Four curves designated as I, II, III, and IV are shown in the figure. \(P_b\) is the bubble point pressure of a crude oil at the given temperature. Which ONE of the following options correctly depicts the solubility of asphaltene (\(q_a\)) in the crude oil with pressure (\(P\)) at a given temperature? \begin{center} \includegraphics[width=0.7\textwidth]{03.jpeg} \end{center}
Which ONE of the following CANNOT be obtained from pressure transient analysis in well testing?

The drainage oil-water capillary pressure data for a core retrieved from a homogeneous isotropic reservoir is listed in the table. The reservoir top is at 4000 ft from the surface and the water-oil contact (WOC) depth is at 4100 ft. 
 


Assume the densities of water and oil at reservoir conditions are 1.04 g/cc and 0.84 g/cc, respectively. The acceleration due to gravity is 980 m/s². The interfacial tension between oil and water is 35 dynes/cm and the contact angle is 0°. 
The depth of free-water level (FWL) is .......... ft (rounded off to one decimal place). 
 

Consider the following diffusivity equation for the radial flow of a fluid in an infinite and homogeneous reservoir. \[ \frac{1}{r} \frac{\partial}{\partial r} \left( r \frac{\partial P}{\partial r} \right) = \frac{1}{\eta} \frac{\partial P}{\partial t} \] where, \( P \) denotes pressure, \( r \) is the radial distance from the center of the wellbore, \( t \) denotes time, and \( \eta \) is the diffusivity constant. The initial pressure of the reservoir is \( P_i \). The condition(s) used in the derivation of analytical solution of the above equation for pressure transient analysis in an infinite acting reservoir is/are: