Basic Sciences in GATE PE
The Science domain tests geology, geophysics, fluid properties, and thermodynamics as applied to petroleum systems. Expect calculations involving rock and fluid properties, phase behaviour, and basic heat transfer.
Core rules and concepts
- Porosity: (\phi = V_p / V_b). Permeability follows Darcy's law; k depends on pore geometry and fluid saturation.
- Fluid properties: oil formation volume factor ((B_o)), gas solubility ((R_s)), viscosity correlations (e.g., Standing), and gas deviation factor (z-factor).
- Phase behaviour: bubble point (first gas bubble), dew point (first liquid drop), and retrograde condensation.
- Geophysics: seismic two-way time to depth conversion using interval velocity.
- Linear Darcy flow in field units: (q = \frac{0.001127 k A \Delta P}{\mu L}), with q in bbl/day, k in md, A in ft², (\Delta P) in psi, (\mu) in cp, L in ft.
Worked example
Calculate linear flow rate for k = 50 md, A = 10 ft², (\Delta P) = 200 psi, (\mu) = 2 cp, L = 5 ft. (q = (0.001127 \times 50 \times 10 \times 200) / (2 \times 5)). Numerator: 0.001127 × 50 = 0.05635; × 10 = 0.5635; × 200 = 112.7. Denominator: 10. q = 11.27 bbl/day. Check that the constant is 0.001127, not 1.127.
Traps that cost marks
- Using 1.127 instead of 0.001127 for field-unit linear flow.
- Forgetting to convert acres to ft² when area is given in acres.
- Using viscosity in Pa·s instead of cp.
- Applying the ideal gas law without the z-factor at high pressure.