Annular Fluid Expansion (AFE) Awareness

1

What is Annular Fluid Expansion?

• A force generated when fluid is heated, then expands in a sealed void between concentric well bore tubulars(annulus)

• It is a very common occurrence in oil and gas production operations.

• Annulus pressure increases can be caused by:

− Leaks between casing strings

− Leaks from the formation into the casing

− A sealed annulus that contains fluid that undergoes thermal expansion.

Source of Temperature Increase in an Annulus

• Bringing a well on-line – Changes the well temperature from the ambient temperature to the flowing temperature (under 40oF to over 150oF).

• Changes in flow rate or water content – Can result in a change in the flowing temperature. This temperature change can affect annulus pressure.

• Pumping operations – Pumping warm fluids down a wellbore or annulus can cause thermal expansion on other annuli. Stainless Steel Hydraulic lines running from the wellhead to SSSV or chemical injection mandrel are at risk as well.

− HOTS / Thaws / Circ Outs

− Identify all wellhead gauges during prejob walkdowns. Discuss pressure limits of these lines with WSLs and Pad Ops whenever adding heat to the system. Monitor these gauges during the job.

The basics…..

Fluid expands as it is heated

Gas is compressed and heated

Pressure Increases

Diesel and Crude, for example,

increase in volume by about

0.0004% per 1oF temperature rise

This may not sound like much, but

let’s look at some examples to put

it in perspective

A fluid packed vessel will build pressure much

more rapidly than one with a gas cap

Fluid Packed

No room for fluid to expand

• 10 bbl vessel

• 50% gas and 50% diesel

• Initial pressure 0 psig

• Initial temperature is 32oF

What is the pressure when the fluids

are heated to 212oF?

Effect of Temperature with large gas cushion

Diesel or Crude

expanding . . .

Gas

Compressed by

expanding diesel and

warmed by

temperature change

If we maintain an adequate gas

cushion, the total pressure rise is

slight.

Example 1

8

The lower the initial gas volume you

have in the system, the higher the

pressure goes and the faster it gets

there!

The effect of pressure with a small gas cushion

Example 2

• 10 bbl vessel

• 7% gas and 93% diesel

• Initial pressure 0 psig

• Initial temperature is 32oF

What is the pressure when the fluids

are heated to 212oF?

470

The higher the initial pressure you

have in the system, the higher the

pressure goes and the faster it

increases.

Importance of the lowering the starting pressure!

Example 3

• 10 bbl vessel

• 7% gas and 93% diesel

• Initial pressure 100 psi

• Initial temperature is 32oF

What is the pressure when the fluids

are heated to 212oF?

3640

What happened at A-22?

A-22 Annulus Pressure Build Up

• A-22 was brought online

• The OA temperature increased

from 45º F to 115º F

• The OA fluid level is rose from

85 ft to 40 ft due to expansion

of fluids in the OA

• The expansion of fluid and

subsequent compression of

gas resulted in ruptured

surface casing 17 ft below

ground

• Cellar boards and debris

knocked off the IA valve

jewelry

• Gas in the IA vented into the

well house

• Damaged electrical equipment

provided an ignition source.

A-22 Annulus Pressure Build Up

Well

brought

online

Pressure increase with temperature for gas and liquid (constant volume)

2000psi

FL (85 FT)

FL (40 FT)

A-22 Annulus Pressure Build Up

Estimated pressure build up of OA:

Assumptions

Starting gas pressure = 2000 psi

97% liquid column, 3% gas column (150 bbls total volume)

Change in temperature 45º F to 115º F = 70ºF

Final Pressure = psi7700

Effect of High Initial Starting Pressure

Higher starting pressure can result in much higher final

pressure if not bled off prior to bringing the well online

Well Pressure as Temperature Increases

0

2,000

4,000

6,000

8,000

40 60 80 100 120 140

Temperature, F

Pre

ss

ure

, p

si

Using the exact same

conditions, a starting OA

pressure of 1000 psi

would not pressure over

1600 psi

1000 psi

1600 psi2000 psi

7700 psi!

How Accurate is the Pressure Gauge Reading?

• On-line wells are required to have functional pressure gauges that are readable on all annuli. Stop

pins are required on all gauges.

• They may be under water in the spring and not readable. Installing gauge risers is an option to get

the gauges above any cellar water.

• The chemical “ Squirt Truck” is used to pump methanol into valve jewelry, reducing the chance of

freezing in cold conditions.

• Replace any pressure gauges you find that are malfunctioning.

• Gauge accuracy can be affected by the range of the gauge, calibration of the gauge, and the

potential for ice or hydrates in the gauge

When checking gauges,

ensure there is a stop pin

to prevent the gauge from

wrapping.

Even a gauge with a stop

pin can be damaged. If a

gauge is pressured

beyond it’s designed

operational range, it may

not read correctly

afterwards.

Well Conditions that could Result in High Annulus Pressure

• A well that has had a recent MIT (valves

tagged and AFE sign on wellhead)

• A new well or RWO

• A well with high IA pressure and no live

GLVs

• A well that has recently had the flow rate

increased (opened choke)

Bleeding

• Bleed vs. shut in. If annulus pressure is excessive, shut in the well and let it cool down.

• Order of preference for tie-in points:

1) Tree Cap or Flow Cross

2) Flow Line

3) Bleed Trailer

Equipment:

- Use hose rated for gas/fluid and pressure

- Check hoses for cracks, bubbles or kinks

- Check JIC Swivel. Replace if loose, worn, galled, cracked, over- torqued or damaged

• Attach the hose, install the whip check, fully open inner valve, throttle using outer needle/quarter turn valve, pressure test hose to operating pressure before starting bleed.

• When in doubt, refer to your local bleed procedures.

JIC Swivel: If there is any question about its integrity, replace it!

What is a Safe Annular Pressure?

• Every well has a Maximum Operating Annulus Surface Pressure (MOASP) documented in AnnComm and Digital Wellfile. These pressures are based on the type of well construction and specific well considerations.

• Wells that cannot be operated safely must be shut-in until repairs or further evaluation are conducted.

Summary

• Annular Fluid Expansion is common in oil and gas production operations throughout the industry

• Annular Fluid Expansion can be safely managed

• Liquid filled or nearly liquid filled annuli build pressure very quickly when the well heats up

• Bleed the annulus pressure off prior to bringing a well online

• Be ready to bleed if needed while the well is warming up

• Monitor the well frequently while it is warming up regardless of whether the annulus is fluid packed or not

• Bleed the well as needed to keep annulus pressure from breaking MOASP

• Continue monitoring until the well is thermally stable and pressure stops increasing

• Log all bleed events into your Operator notes database: “Bled OA 1200/500 5 min - gas”

• Report all wells with annulus pressures that go over MOASP, or any other anomalies, to the Well Integrity Engineer (x5525) or the Well Integrity Coordinator (x5102) and submit an anomaly report