Wellbore Schematics

• Potential

– An informative layout drawing of what is in the well,

• Problem

– Accuracy is not always good,

– Incomplete or erroneous schematics can seriously

mislead a design and may lead to a serious failure.

– Well components change with time:

• Replacements not recorded

• Corrosion or damage weakens the components.

Example Schematic – sub sea well

What information is available on new well?

1. Pipe size, end of the string.

2. Location of restrictions.

3. Deviations, dog legs

4. Overlaps

5. Shoulders

6. Pay

7. Fluid behind the pipe

8. Other BHA

9. Damage locations?

But that’s not all the information that is

there.

Header Information

WELL TYPE: OIL PRODUCER RTE: 29m MAX DOGLEG: 6.184 deg @ 1725m

FIFST COMPLETED: 22/12/96 SWAB: MAX DEVIATION: 89 deg @ 4456M

WORKOVER DATE: MAY 2001 KOP: 2290M AV. ANGLE THRU PAY: 88 deg.

WORKOVER NO: 1 HUD: MINIMUM I.D.: 4.060 @ LTV

ANN. FLUID: CaCl2 BRINE DEPTH UNITS: METRES

FLUID WT: 1.17 SG REF. LOG: XXXXX

Some points of interest:

Profile locations

Trapped annuli

Restrictions

SSSV

Gas lift valves

Ledges/shoulders

Crossovers

EOT (end of tubing)

PBTD, plugs of any type

Kick-off points

Fluid entry areas

Fish

Damage

Debris

Doglegs

Components – size, grade, id, position

Mixed equipment

• What is the pressure rating of this well?

Sometimes components are mixed in a well, often with the aid of crossover pieces to

adapt fittings of different pressure ratings. The pressure rating is set by the current

strength of the lowest strength piece. Actual testing is required to determine the level of

working pressure. When damage is known to have occurred, the components must be

tested, isolated or replaced.

Flanges

Nominal

Size of

Flange Casing Size

Diameter of

Flange

Diameter of

Bolt

Circle

Number of

Bolts Ring Type

2-1/16 2-3/8 8-1/2 5-1/2 8 R-24

2-9/16 2-7/8 9-5/8 7-1/2 8 R-27

3-1/8 3-1/2 11 8-1/2 8 R-37

4-1/16 4-1/2 12-1/4 9-1/2 8 R-38

5-1/8 5-1/2 14-3/4 11-1/2 8 R-44

7-1/16 7 15-1/2 12-1/2 12 R-46

11 9-5/8 23 19 12 R-54

13-5/8 16 30-3/8 26-5/8 16 BX-160

5000 psi, Type 6B

Valves

Above and Below: Gate valve

seals and bar – common in

wellheads.

Right top: plug

valve – common

in surface

treating “iron”

Right center:

dowhole flapper

valve.

Right lower:

butterfly valve

common on

tanks.

Note: open a valve fully (count

the turns) and close it fully (also

count turns) – throttling flow with

a valve will lead to erosion.

Profiles

Pay Interval Schematic

1. Where are the fluid entry points

1. From the wellbore

2. From the reservoir.

2. Will the interval between the sceens pack

during gravel packing?

3. Will ECP’s inflate? How long is the slide?

How rough? What deviation? What fluid is

use to inflate? What is the stability and

permeability of the set point?

Limited Schematics

Artists renditions – too much missing.

Problems in a deviated well arise around kickoff points (window

debris, sharp edges, doglegs), build angle, junction isolation quality

and changes in angle along the horizontal plane.

Detailed information drawing.

Potential Problems:

Open shoe at 16”x20”

“C” annulus.

Trapped or sealed

annuli on A and B.

Fill tag at 12,845’

Tubing cut at 12,933’

Completions Section – What are the clearances, hot spots, entries, etc.

What is below the current

completion may influence

what can be done in a

workover.

Plug quality

Leak potential from high

pressure gas or water

zones.

Corrosion potential of lower

zones

Upper section of a dual, note packer,

15

15a

15a

Bottom zone of a dual completion with sand control. Note clearances, screen location with respect

to pay, isolation potential, method of stacking the completion, and opportunities for problems.

Another style of well bore

schematic.

Note that the level of detail is

different – not as much

information on the individual

jewelry.

Note that the I-1 upper

completions is a sand control

completion with the long

string passing through a

screen. This needs a blast

joint to protect against long

string leaks and failure.

Good isolation in most cases.

The I-5 Sand is a non-

perforated future alternative

pay. In this configuration,

how could it be completed?

Note how the completion is

separated, allowing packing

of the L-4 and then building

the upper completions.

Gas Lift Valve Locations:

Depth

Size?

Dummied or Active?

Condition?

Red Flags - Restrictions

• In the design/drill

– Profiles

– Some connections

– Crossovers

– SSSV’s

– Doglegs

– Deviated sections

• Production

– Scale

– Organic ppts.

– Salt

– Tubular deformation

– Fish

– Fill

Workover Concerns

• Tubing end – entry of tool strings

• Latching plugs and fish

– Deviated set points

– Fill

• Swell of elastomers on plugs

• Swell and bow in fired perforating guns

• Overlap sections for perforating

• Liner tops (leaks)

• How to circulate out the back side.

Common Mistakes and Errors

• Schematic not current: – Last redesign, workover, failure not listed.

– Corrosion, fill, collapses, or fish not listed.

– Does pipe/wellhead need to be derated?

– Deviation shortens tool length that will run through the bend.

• So, how do you know what’s there? – Drift / tag, bailer, dummy tool runs, impression blocks,

camera…

– Talk to the field and last engineer who had the well.