Crude Oil Emulsions: 2021 #8

The statement most false regarding emulsions is:
A) Mechanical equipment available for breaking oilfield emulsions includes free water knockout drums, three-phase separators, desalters, and settling tanks.
B) Sedimentation and creaming are driven by the density differences between oil and water.
C) Coalescence is an irreversible process that is enhanced by low water cut.
D) Demulsification, the separation of emulsion into its component phases, is a two-step process.

Click the buttton for the answer, with commentary. Feel free to ask questions.

C) Coalescence is the second step in demulsification. During coalescence, water droplets fuse or coalesce together to form a larger drop. This is an irreversible process that tends to a decrease in the number of water droplets and eventually to complete demulsification. Coalescence is enhanced by the following factors. High water cut increases the frequency of collisions between droplets. (HS1 P552).

Vertical Separator: 2021 #7

This is a fairly simple problem; merely the first step in sizing a vertical separator. That is, to calculate the vessel diameter based on gas capacity. I'll add in the other steps on some other practice problem set, as this is a low-priority study area considering horizontal separators are far more common.

A slight wrinkle (there's always one of those, right?) is needing to calculate the density of the gas and oil first. Needed constants: page 190 of the Reference.

Reservoir Geology: 2021 #6

#6 is fairly tough merely because few stay familiar with geologic terms, even many who work as reservoir engineers. Subjects like this make can the PE exam tricky; it's unlikely the exam will go too deep "into the weeds" on any specific subject, but it may, and so one should be prepared. 

Note that everything in this problem is directly out of the first 15 pages of SPE HS5, so it's definitely basic, and thus "fair game". 

If you think the problem missed something relevant, please note them in the comments!

Mud Calculations: 2021 #5

A rig has 950 bbl of 9.5 lbm/gal, 5% solids content mud. To deal with a high-pressure zone over the next hole section 800 bbl of 14 lbm/gal, 3% solids content mud is needed. Assuming the rig dumps and dilutes before deciding to use 14 lbm/gal mud, the quantity of barite required (sacks) is closest to: A) 1,800; B) 2,000; C) 2,200; D) 2,400.

Click the button for the answer, commentary, and references sourced. Feel free to leave comments or questions.

This is a real-world problem type similar to one in TS12, P106-107, so know how to do it. There are four basic steps:
1. Dump 150 bbl of the 9.5 lbm/gal mud for the required 800 bbl (note this is still 5% solids content mud).
2. Dilute the mud's solid content from 5% to 3%. Since solids are a mixture the dilution calculation is simple: 800 bbl(0.03/0.05) = 480 bbl (20,160 gal) of 5% and 320 bbls of "something else" to make 800 bbl (33,600 gal) of mud with of 3% solids.
3. Weight up to 14 ppg, so our "something else" is barite and water (that is, 4 additives; i=initial mud, w=water, b=barite, f=final mud).
Equations required: mass and volume balance mi+mw+mb=mf and Vi+Vw+Vb=Vf (units lbm and gal). 2 equations, 2 unknowns, so can be solved.
4. Solving the equations:
20160*9.5+mw+mb=33600*14 and 20160+Vw+Vb=33600.
191520+mw+mb=470400 and Vw+Vb=13440.
mw=278880-mb and mw/8.33ppg+mb/35ppg=13440.
mw=278880-mb and 0.12mw+0.02857mb=13440.
0.12(278880-mb)+0.02857mb=13440.
33466-0.12mb+0.02857mb=13440.
-0.09143mb=-20026.
mb=219,000 lbm = 2190 sks barite or C). [Source: TS 12 P106-107]

Remember to keep three significant digits on mud problems. I made this problem similar to one in TS12 as they solve it using equations that you won't have on this exam, but it's possible a few of you may be steely-eyed missile men and have them memorized. If so, this way you can check your method's results there.

Note this would be a very hard problem for the exam; I would say only 1/10 could get this correct in a reasonable time, so don't despair, keep at it until you understand all the different ways the problem could go. Once you've practiced these types of problems you can crank them out with ease.

Mud: 2021 #4

True statements about drilling fluids include (select any that apply):
__ The majority of wells today are drilled with water-based drilling fluids.
__ The use of pneumatic drilling fluids is limited to depleted zones or areas where the formations are low pressured.
__ Polymers are used to prevent clay dispersion in freshwater or seawater-based drilling fluids.
__ Oil-based fluids typically include 10-40% water.
__ One function of a drilling fluid can be categorized as: ensure maximum logging information.
__ One function of a drilling fluid can be categorized as: support part of the drillstring and casing weight.
__ Poor fluid loss control can cause surge, swab, and circulation-pressure problems.

Click the button for the answer, along with commentary and SPE references sourced. Note that the provided SPE Reference Guide will not help at all on these types of problems. Feel free to ask questions in the comment box below.

True statements about drilling fluids include (select any that apply):
 X  The majority of wells today are drilled with water-based drilling fluids.
 X  The use of pneumatic drilling fluids is limited to depleted zones or areas where the formations are low pressured.
 X  Polymers are used to prevent clay dispersion in freshwater or seawater-based drilling fluids.
 X  Oil-based fluids typically include 10-40% water.
 X  One function of a drilling fluid can be categorized as: ensure maximum logging information.
 X  One function of a drilling fluid can be categorized as: support part of the drillstring and casing weight.
 X  Poor fluid loss control can cause surge, swab and circulation-pressure problems.

Note that this "multi-choice" format in the new EBT exam makes it extremely difficult to know if you have it fully correct. The 2021 practice problem sets have many in this format (likely more than the real exam) because it's a good way to test knowledge.

Source HS2 (P89-93).
The majority of wells are drilled with water-based drilling fluids (P91).
The use of pneumatic drilling fluids (i.e. air, gas, and foam)is limited to depleted zones or areas where the formations are low pressured (P90).
Polymers are used to provide viscosity, fluid-loss control, shale inhibition, and prevention of clay dispersion in freshwater or seawater-based drilling fluids (P91).
OBF: The oil/water ratios typically range from 90:10 to 60:40 (P93).
The function of a drilling fluid can be categorized as: ensure maximum logging information (P89).
The function of a drilling fluid can be categorized as: support part of the drillstring and casing weight (P89). Poor fluid loss can cause surge (an increase in wellbore pressure under a bit from running into the hole), swab (a decrease in wellbore pressure under a bit from running out of the hole), and circulation-pressure problems (known as ECD) (P89).

Well Control: 2021 #3

When drilling an oil well using a rig with a 850 bbl mud system a sand was encountered from 9,000 ft to 10,200 ft. Reservoir pressure was measured at 4,950 psi.

Drilling ahead with a 9.8 lbm/gal mud weight continued until 12,000 ft, at which time the ROP rapidly increased and a kick suspected so the well was shut in. Drillpipe pressure was recorded at 650 psi. Company policy requires a trip margin of 200 psi; the barite (sacks) needed is closest to: A) 700; B) 705; C) 710; D) 715.

Click the button for the answer, commentary, and the SPE Reference Guide pages sourced. Feel free to leave comments or questions.

This problem requires basic drilling knowledge, has three distinct steps with two tricks. But all the needed equations are provided in the SPE Reference. One factor not provided in the Reference is how a "trip margin" fits into the equations; you can explore this subject in TS12 or the Guidebook (3 HYD 5).

FP = (9.8*0.052*12,000)+650 = 6,765 psi. [SPE RG P41, P47]
Note how the first reservoir pressure is a red herring, but many get fooled by this sort of misdirection.

KWM = (6,765 psi + 200 psi)/(0.052 psi-ft/ppg*12,000 ft) = 11.162 ppg. [SPE RG P48]
Trip or kick margins (given in pressure here) can be in ppg as well (the Guidebook has a section on trip and kick margins; these are tricky and you won't get any help from the provided SPE Reference Guide).

Barite = [1470*((11.162-9.8)/(35-11.162))] = 83.989 sks/100 bbl = (84 sks/100 bbl)*(850 bbl)=714 sks. [SPE RG P45]
Never forget this equation uses per 100# sk/100 bbl.
D) 715 sks.

Flanges: 2021 #2

Which statement about oilfield flanges is false? 

A) Flat-face flanges are typically available only in low-pressure and are not used in high-pressure applications.
B) RF and RTJ flanges are commonly used in the oil and gas and pipeline applications.
C) RTJ "ring" gaskets are typically made of cadmium-plated soft iron or low-carbon steel for ANSI 600 and ANAI 900 class flanges.
D) When an API flange is bolted to an ANSI flange, the connection must be rated for the API pressure rating.

Click the buttton for the answer, with commentary. Feel free to ask questions.

D) When an API flange is bolted to an ANSI flange, the connection must be rated for the ANSI pressure rating. Source HS3 P355-357.

Separators: 2021 #1

A separator may contain which of the following to aid in the separating of the gas, oil, and water streams (select any that apply):
__ Inlet diverters
__ Outlet vortex breakers
__ MAWP limit switch
__ Vapor pressure overflow drum
__ Turbo-expander system
__ Sweetening tube (low-psi)
__ Buckets
__ Weirs
__ Mist extractors

Click the button for the answer, with commentary and SPE Reference Guide pages sourced. Feel free to ask questions.

A separator may contain which of the following to aid in the separating of the gas, oil, and water streams (select any that apply):
 X  Inlet diverters
 X  Outlet vortex breakers
__ MAWP limit switch
__ Vapor pressure overflow drum
__ Turbo-expander system
__ Sweetening tube (low-psi)
 X  Buckets
 X  Weirs
 X  Mist extractors

Note that this "multi-choice" format (appearing on the new EBT exam last year) can make a problem extremely difficult, as this one is. The new practice problem sets will have quite a few of these, more than the real exam for sure, merely because it's a good way to test knowledge.

Source HS3 P3: The first step in the process is separating the gas from the liquid and the water from the oil. This is usually done in a separator - a pressure vessel into which the well-stream flows to allow the gas, oil, and water to separate because of gravity. Separators may contain inlet diverters, outlet vortex breakers, buckets, weirs, and mist extractors to aid separating the streams.