Reading a wellbore Schematic

Wellbore Schematics • Potential – An informative layout drawing of what is in the well,

• Problems – 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.

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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.


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Header Information WELL TYPE: OIL PRODUCER FIFST COMPLETED: 22/12/96 WORKOVER DATE: MAY 2001 WORKOVER NO: 1 ANN. FLUID: CaCl2 BRINE FLUID WT: 1.17 SG

RTE: 29m SWAB: KOP: 2290M HUD: DEPTH UNITS: METRES REF. LOG: XXXXX

MAX DOGLEG: 6.184 deg @ 1725m MAX DEVIATION: 89 deg @ 4456M AV. ANGLE THRU PAY: 88 deg. MINIMUM I.D.: 4.060 @ LTV


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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


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Components – size, grade, id, position


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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.


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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

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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

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19

12

R-54

13-5/8

16

30-3/8

26-5/8

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BX-160

www.GEKEngineering.com 5000 psi, Type 6B

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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 www.GEKEngineering.com count turns) – throttling flow with a valve will lead to erosion.

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Profiles


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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?


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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.


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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’


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Completions Section – What are

the clearances, hot spots, entries, etc.


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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


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Upper section of a dual, note packer,

15a

15 15a


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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.


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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 nonperforated 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.


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Gas Lift Valve Locations: Depth Size? Dummied or Active? Condition?


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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


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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. www.GEKEngineering.com

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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. www.GEKEngineering.com

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