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24-Pet-A5 Petroleum Production Operations · December 2014

Question 4 of 5: Electrical Submersible Pump (ESP) Sizing

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Exams December 2014 — 98-PET-A5 Petroleum Production Operations (3 hrs, open book). Reference texts: Golan & Whitson, Well Performance, 2nd ed.; Ahmed, Reservoir Engineering Handbook, 5th ed.; Brown, The Technology of Artificial Lift Methods, Vol. 2a–4; Beggs, Production Optimization Using Nodal Analysis, 2nd ed.; Craft & Hawkins, Applied Petroleum Reservoir Engineering, 3rd ed.

Question 4: Electrical Submersible Pump (ESP) Sizing (25 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given.

Well depth / ESP set depth8000 ft / 7000 ft
Productivity index, $J$ / $\bar P_r$1 bbl/day/psi / 3000 psi
Oil gravity / gas gravity35°API / 0.65
Formation GLR100 SCF/STB (half separated at pump)
Casing ID below pump6 in.
Total liquid rate, $q_L$1200 STB/day
Casing flowing gradient$dP/dL=0.0001\,q$ psi/ft
$P_{wh}$ / tubing ID160 psi / 2.441 in.

Find. The required ESP horsepower.

Check: no pump/motor mechanical efficiency is given, so the boxed figure below is the hydraulic horsepower the fluid column itself demands ($Q\cdot\text{TDH}\cdot\text{SG}/3960$); an installed motor nameplate would be sized higher to cover a typical 50–65% pump efficiency (roughly 25–30 HP). Friction losses in the tubing above the pump are folded into the same homogeneous no-slip gradient used in Question 3 (no separate friction correlation or viscosity was supplied in the source for the tubing leg, only the casing $dP/dL$ formula below the pump).

Approach. Use the IPR to fix $P_{wf}$ at total depth, subtract the given casing flowing-gradient loss to reach the pump intake, compute the required pump discharge pressure by carrying the surviving (half) free gas up the tubing to $P_{wh}$, and convert the resulting differential pressure to head and hydraulic horsepower.

  1. Flowing bottomhole pressure. $P_{wf}=\bar P_r-q_L/J=3000-1200/1=1800$ psi at 8000 ft.
  2. Pump intake pressure. $dP/dL=0.0001\times1200=0.12$ psi/ft over the 1000 ft casing interval (8000 to 7000 ft): $\Delta P=120$ psi, so $\boxed{P_{intake}=1800-120=1680\ \text{psi}}$.
  3. Gas split at the pump. Formation GLR = 100 SCF/STB; half is separated and vented up the casing-tubing annulus, half (50 SCF/STB) continues up the tubing with the liquid.
  4. Required pump discharge pressure. Marching the homogeneous no-slip mixture (GLR = 50 SCF/STB, oil SG = 0.850) downward from $P_{wh}=160$ psi at surface to 7000 ft gives $\boxed{P_{discharge}=2422\ \text{psi}}$.
  5. Pump differential and TDH. $\Delta P_{pump}=2422-1680=742$ psi. Converting to head using the mixture's own density at average pump conditions ($\rho\approx50.1$ lbm/ft$^3$, gradient $=0.348$ psi/ft): $\text{TDH}=742/0.348=\boxed{\text{TDH}=2133\ \text{ft}}$.
  6. Hydraulic horsepower. $Q=1200\ \text{STB/day}\times42/1440=35.0$ gpm; mixture SG at pump $=50.1/62.4=0.802$. $\text{HP}=\dfrac{Q\cdot\text{TDH}\cdot\text{SG}}{3960}=\dfrac{35.0\times2133\times0.802}{3960}=\boxed{\text{HP}=15.1}$.
ESP0 ft, P_wh=160 psi7000 ft: ESP intake 1680 psi / discharge 2421.6 psi8000 ft: perfs, P_wf=1800 psitubing6 in casing (below pump)
Fig. 4 — ESP completion schematic: pump set at 7000 ft, intake/discharge pressures, and the reservoir/perforation datum at 8000 ft.
QuantityValue
$P_{wf}$ (8000 ft)1800 psi
Pump intake pressure (7000 ft)1680 psi
Pump discharge pressure required2422 psi
Pump differential pressure742 psi
Total dynamic head, TDH2133 ft
Required ESP hydraulic horsepower15.1 HP