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Relief lines are sized to each individual well test and are provided to relieve over-pressure and prevent catastrophic rupture of lines or vessels.

Emergency shutdown systems are also provided, both linked to automatic and manual pilots to secure the well in the event of equipment failure.

1.7

HIGH PRESSURE / TEMPERATURE WELL TESTING

High temperature is possibly the greatest problem to overcome during high pressure/temperature well testing. If using a Coflexip hose from the surface test tree to the choke manifold then the flowing temperature must be limited to below 250F, this is achieved by choking back the well.

One way of choking back the well is to fit a hydraulically controlled choke (Masterflo) onto the flow-wing outlet of the test tree, this would have a cooling affect on the fluids immediately downstream. Alternatively the well can be choked back at the choke manifold.

The Coflexip hose could also have water hoses directed on it eg. from fire monitors, which would also have a cooling effect on the Coflexip.

To overcome the possible problem of elastomeric seal failure through the breakdown of the rubber, EXPRO use Grayloc clamp connectors providing a metal-to-metal seal on all pipework upstream of the heater. The choke on the heater will provide a cooling affect further reducing the temperature.

NOTE: For gas wells where high temperatures are encountered the main problem is in the 'flashing off' of condensate to a gas phase meaning that no P.V.T. samples can be collected for recombination from the separator.

1. EXPLOSIVE DECOMPRESSION

One of the major problems encountered in testing high-pressure wells, is the problem of explosive decompression. This phenomenon causes problems in that when seals are compressed under high pressure some gaseous elements diffuse into the seal. If a rapid pressure drop occurs or after frequent pressure cycling, materials not resistant may suffer extensive damage, usually in the form of splits and/or blisters. This is because the entrained gas expands against the elasticity of the rubber causing severe internal damage that may split or rupture the elastomer.

This problem is especially prevalent where there is a high CO2 content in the well gas stream and if this is the case then explosive decompression may occur at relatively low pressures. This is due to the ability of the CO2 to permeate the elastomers.

NOTE: The CO2 has no chemical affect on the elastomer it is a purely physical phenomenon.

The critical parameters most likely to affect Explosive Decompression performance are:-

a) gas type

b) pressure and decompression rate

c) temperature

d) soak time at pressure

e) seal volume and exposed seal surface area

f) initial squeeze (strain exerted on seal while rigging up hammer union).

One type of rubber seal designed to overcome this problem is the Anson Superseal which is based on Viton B (a high fluorine content fluoroelastomer) which is given the compound name FR 58/90 (the 90 refers to the hardness of the rubber).

The level of fluorine in the elastomer is thought to have a major effect on the solubility of gas in the seal and thus resistance to ED as does the hardness of the elastomer.

NOTE: Materials above 85 IRHD generally give greater resistance to ED.

ie. The harder the elastomer seal the greater the resistance to gases permeating into it. The downside of this is that the harder the seal, the worse the sealing properties. If possible, bleeding down systems slowly will help prevent explosive decompression occurring. For High Pressure Well Testing, to avoid any possibility of ED failure of elastomers, EXPRO use metal-to-metal seals (in form of clamp connectors) for all pipework upstream of the heater inlet ie. the high pressure process equipment. This avoids totally the possibility of explosive decompression.

1.7

HIGH PRESSURE / TEMPERATURE WELL TESTING

When unloading a heavyweight brine cushion or similar there exists a possibility that with a needle and stem type adjustable choke, that the seat may "back-out", even though a copper gasket has been fitted.

This is due to the nature of the "heavy" fluids passing through the choke at high pressure, where turbulence is set up as the flow passes the adjustable stem and cone. As this fluid passes through the choke seat, the drag it exerts may be large enough to cause the seat to "back- out", even though it may have been torqued tight. The recommended torque for this type of adjustable choke is in the nature of 1500 ft/lbs and to achieve this by using an ordinary choke spanner may prove difficult. If this is the case then a "cheater" bar should be used.

NOTE: It may be desirable to use a torque wrench to achieve the correct torque rates.

Refer to Section 3.26.3 for further information.

It is also possible for the adjustable choke cone to shear off the stem. This is also due to the forces created by the turbulence created by the "heavy" fluid passing through the choke.

If there is any doubt as to whether a choke seat (or bean) has worked loose, then flow should be diverted to a similar sized choke on the other side of the manifold and the suspect choke inspected.

NOTE: a) Flowing through a choke where the seat/bean is not properly installed can cause damage to the internal threads for the seat/bean in the choke body and/or erosion of the body itself.

b) This will not only be a safety hazard but will also result in a major refit of the choke assembly.

1.7.2 SUB-SURFACE CAPABILITY

In addition to the surface equipment EXPRO have a range of annular controlled sub-surface DST tools (EXACT range). These tools have been developed with 15,000 psi and 400°F capability. By combining new design concepts with advanced metallurgy and elastomer technology, these EXACT tools are compact, robust and combine operational safety with ease of use.

1.7.3 DATA ACQUISITION

To complement our high pressure well test equipment and increase overall safety, an upgraded Data

Acquisition system is provided to acquire Bottom Hole Data, via memory gauges, Ameradas and carriers), and Surface Data, via the Surface data Logger. This Data Logger will play an important part in the central monitoring and control of testing operations and temperatures can be monitored easily at any point in the process train.