ESP: 2017 #19

ESPs have many testing options. In this problem, we are given:

1) SG of the working fluid (10% water SG 1.01, 90% oil SPI 40)
...so SG = 0.1(1.01) + 0.9(0.8244) = 0.84

2) Net Lift 3,500 ft, Friction 300 ft, Surface pressure 200 ft
...so TDH = 3,500 + 300 + 200 = 4,000 ft

3) ESP with head capacity 4,000 ft/100 stages and 1 BHP/stage:
...4,000 ft / (4000 ft/100 stages) = 100 stages
...so BHP = (1 BHP/stage)100 stages(0.84) = 84 BHP

Fairly simple. If you aren't familiar with all three steps before seeing the problem it's hard to do it quickly. So be familiar with all three steps.

ESP: 2018 #43

Problem 43. The following statement concerning troubleshooting an ESP most FALSE is:

(A) The major source of info troubleshooting an ESP...
(B) Gas locking is marked by amperage decline...
(C) Solids are spotted by amperage fluctuation...
(D) Fluid pumpoff is detected by slow amperage decline..

This is a fairly tough problem to my mind. Let's count the ways:

1. It claims "the" major source for ESP troubleshooting is the ammeter? Really? Come on, the major source? I can imagine quite a few sources, and "the major source" a definite statement. But this is also a direct quote from an SPE source (Bradley) so consider it gospel. It's also in the Guidebook.

2. The gas locking question is fair, not hard to find. You can get that even if you don't know anything about ESPs.

3. "C" is a little harder, but again with a few minutes of good sources you can find this one.

4. "Fluid pumpoff" is indeed detected by slow amperage decline often due to oversized pump (not an undersized one). Again, this is a direct quote from the Guidebook (and that same pesky Bradley source). But it's a fair question; one should know this if you understand ESPs.

Note it's easy to misread this kind of problem because it gives a correct fact first and only then gives slightly incorrect second part.

ESP: 2018 #42

Problem 42. Designing an ESP installation from given data, the TDH (ft) is closest to: 
Current production: 500 BFPD at 500 psi drawdown.
Desired production: 4X (negligible free gas, annulus friction). 
Pressures (psi) at 2M BFPD: Pump-intake/wellhead = 1M/200. 
Depth (ft) of pump at perfs = 6M; Friction loss = 41.7 ft/1M ft tbg. 
WC: 80%, 1.0625 SG; OC: 20%, 0.91 SG & 24 API. 
(A) 4,460 (B) 4,660 (C) 4,860 (D) 5,060 

See Guidebook 7 PRD 3-4, or the ESP Sizing Guide reference listed there.
Note: this problem was updated on Kindle after 10/12/2018 as the original given well data was nonsensical (even though it led to the same answer selection). Please use the well info shown above:

1. PI = dq/dp  = 500/500 = 1 bfpd/psi.
2. SGw = 0.8(1.0625) = 0.850; SGo = 0.2(.91) = 0.182; so SGf = 0.85 + 0.182 = 1.032.
4. NDL = Pdepth - PIP(2.31)/SGliq = (6,000 – (1,000*2.31)/1.032 = 3,762 psi ft
5. Hf = 6,000 ft and 41.7 ft/1,000 ft = 250 ft.
6. Hwh = 200 * 2.31 / 1.032 = 448 ft.
7. TDH = 3762 + 250 + 448 = 4460 ft (A).

Because the answer is the lowest TDH option given, any lower value one calculates will give the correct answer.

ESP

Some interesting points regarding ESPs: the older SPE Handbook (Bradley 1987) has two seemingly contradictory quotes on the same page (7-1):

a) The ESP has the broadest producing range of any artificial lift method.

b) The major disadvantage of the ESP is that it has a narrow producing rate range compared with other artificial lift forms.

What is correct?  Here's what the newer SPE Handbook says regarding ESPs:

1. 200 to 20M B/D typical (30M max).

2. High-Volume Lift Capacity excellent

3. Low-Volume Lift Capacity generally poor: low efficiency & high operation costs <400 BFPD. 

4. Limited by needed horsepower.

5. Can be restricted by casing size.

Hard to know what Bradley was trying to say. Just be aware of both SPE sources, and let this be a lesson on how language can make an otherwise simple question more difficult. I like to underline these "money quotes" in pencil in my Handbook when I run across them.