DESCRIPCIÓN DE LA ESTRATEGIA O SISTEMA DE MEDIDAS DE MITIGACIÓN Se aplicarán programas de vigilancia para garantizar la efectividad de las acciones que

Gas lifting may be required to kick-off a well, which contains a kill fluid, in low pressure producers when production has been temporarily halted. It is also used to remove a dead column of fluid from closed tubing. Each specific condition requires an exact programme, however the basic procedure still applies.

When kicking off a well containing a kill fluid follow the basic procedure in this section. Allow sufficient nitrogen to remove any kill fluid that may have entered the formation during the kill operation. As a rule do not use excessive pump rates as this will lead to high annulus friction and nitrogen may be lost to the formation. In wells exceeding 40o deviation nitrogen slippage is likely to occur. You should allow sufficient nitrogen to compensate for this slippage.

When restoring production in low pressure wells that have been temporarily shut in, use low nitrogen rates and only run to a maximum of 50% of well depth. These wells only require encouragement until water cut has been reduced and temperature has risen.

When removing a fixed dead column of fluid from a well, as when creating a nitrogen cushion prior to DST or TCP, follow the main procedure, except that the well will not flow and dry gas should be produced at surface.

The procedures in this section are guidelines only, specific operational programmes will be issued by the Company.

Safety

A safety meeting will be held with all relevant personnel prior to any job. The meeting will address the hazards inherent with handling liquid nitrogen (Refer to section 14.7). The meeting will also address the actions to be taken in the event of an emergency.

Procedures

1) Rig up and test the coiled tubing (Refer to section 13.4)

2) The nitrogen tanks, converter and pumping unit should be positioned close to the tubing reel in order to minimise the length of pressurised lines.

3) Reduce the test separator pressure according to the coiled tubing contractors procedures, and line up the well to the test separator.

4) Allow any gas cap on the well to vent off through the test separator.

5) Confirm that the tree and SCSSV controls have been isolated from the main control system.

6) Equalise pressure across the swab valve then open.

7) Run in the well carefully, stopping to establish nitrogen injection at a low rate, increasing the rate slowly as the coiled tubing is further run in.

• If the well begins to slug nitrogen, reduce the injection rate

• Shut down the nitrogen unit at the first indication of any rapid build up in wellhead pressure.

8) Once the tubing has reached the predetermined depth, stop running in and continue pumping nitrogen until nearly all the nitrogen is pumped, or the well is flowing strongly.

Note: Pull the tubing out of the well before the nitrogen supply is completely exhausted. This is to ensure that the pressure differential across the tubing wall does not exceed 1,000psi.

1) Rig down and hand the well over to the Production Department.

2) The following data will be recorded throughout the nitrogen lift operation:

• Wellhead flowing pressure

• Nitrogen injection pressure

• Nitrogen injection rate

• Wellhead flowing temperature

• Separator level

• Separator pressure

• Separator temperature.

3) Fluid samples will be taken from the flow line sample point by the Well Operations Supervisor.

13.6.2. Well Treatment

Well treatments can be performed using various acid and solvent formulations to improve production or injection rates. Coiled tubing is often used to perform well treatments, because it allows for the direct application of the treatment to the zone or area requiring treatment.

The main types of treatment are as follows:

• Removal of scale from well tubulars and SCSSV

• Matrix acidisation of the formation

• Well bore clean-up using solvents and or acid.

Scale removal can be achieved by circulating acid across the area requiring treatment. Note: Much of the acid may remain unspent and that this may have an effect on

surface flowlines and production equipment. Specific formulations may be recommended by the contractor to remove sulphate scale, and scale containing hydrocarbons.

Matrix acidisation of the formation can take the form of a small acid wash injected from the coiled tubing directly to the zone requiring treatment, or for larger treatments, with the coiled tubing being used to circulate the acid to fill the tubing prior to direct high rate injection from surface. If leaving the coiled tubing in the well ensure that it is sufficiently inhibited and that the internal pressure of the C/T remains equal to or above the external pressure.

Well bore clean-ups are performed to remove scale, debris and waxes from the perforation tunnels. They are not intended to penetrate the formation, which could lead to additional damage. The treatment is applied by jetting the treatment fluid into the perforations while slowly cycling the nozzle across the perforations. The treatment is performed with the well balanced or slightly underbalanced to prevent treatment fluid penetration.

Safety

Prior to rigging up the acid equipment a safety meeting will be held with all relevant personnel (Refer to section 15.5). The meeting will address the hazards inherent with handling acids, particularly under pressure. The meeting will also address the actions to be taken in the event of an emergency.

Procedure

The following details the basic procedures to be followed when performing acid treatments through coiled tubing:

1) Rig up and test coiled tubing (Refer to section 13.4). 2) Suggested BHA is, from the bottom up:

• Jetting nozzle

• 2 dart type check valves

• 6ft straight bar

• Tubing connector.

3) Confirm that the tree and SCSSV controls have been isolated from the main control system.

4) Pig the reel to determine accurate reel volume. 5) Equalise pressure across the swab valve then open.

6) Run in the well carefully, circulating at minimum rate. Perform regular pull tests/checks at 1,000 ft intervals.

7) Once the area to be treated has been reached, pump treated injection quality seawater in order to establish the circulating pressure.

8) If an acid wash or solvent treatment is to be performed then:

• Circulate the coiled tubing to treatment fluid

• ϑet the area to be treated while reciprocating the coiled tubing slowly

• Circulate the tubing to injection quality seawater

• Pull out of the hole.

9) If matrix acidising is to be performed the treatment formulation and volume will be advised in a separate programme. However the basic procedure is:

• Circulate the treatment fluid into the well at the maximum rate.

• Pull the tubing assembly above the acid and inject at a high rate via the tubing and the tubing annulus simultaneously. (Alternatively the coiled tubing can be pulled out of the well before injecting the acid.)

• Pull out of the hole and if required flow the well with nitrogen. Inhibition

It is essential that a sufficient quantity of inhibitor is used in the acid system. If a mutual solvent is being used, the inhibitor content must be doubled due to the detrimental effect that the solvent has on inhibitor efficiency.

A slug (5-10bbl), with 5% inhibitor in injection quality seawater, should be circulated ahead of the acid treatment. This will give protection to both the inside and outside of the tubing.

13.6.3. Sand Cleanout General

1) It may be necessary to clean out sand fill from a well to provide a sufficient sump for production logging, additional perforating and to exposed covered perforations. Sand clean out is best carried out using C/T. The clean out is carried out by running the tubing and pumping viscous fluid (gel) to lift the sand from the sump.

2) The clean-out operation may be carried out with the well flowing to assist the return of sand to the surface. This is especially useful when the well is highly deviated, has a large bore production string or when the well is unable to support a column of gelled seawater without incurring losses.

3) It is essential to keep circulating when there is a sand column in the production tubing. This is especially important when the well is not flowing, otherwise the C/T will become surrounded in sand and stuck.

Safety

Prior to rigging up the coiled tubing and circulating equipment a safety meeting will be held with all relevant personnel. The meeting will address the hazards of handling chemicals and use of pressurised equipment. The meeting will also address the actions to be taken in the event of an emergency.

Procedure

1) Ensure that the well is lined up to take returns to the test separator. Note: The separator should be sand washed prior to the operation. 1) A sample point will be installed in the return line.

2) Rig up and test the coiled tubing (Refer to section 13.4). 3) Suggested BHA is, from the bottom up:

• Jetting Nozzle

• 2 dart type check valves

• 6ft straight bar

• Tubing connector.

4) The required gel system should be prepared in a mixing tank and transferred to a holding tank containing agitators once it is fully hydrated.

5) Confirm that the Xmas Tree and SCSSV controls have been isolated from the main control system.

6) Equalise pressure across the swab valve then open it.

7) Begin running in carefully with the well producing at a reduced rate. Keep the tubing string filled full of treated sea water by circulating at the minimum rate. Carry out regular pull tests/checks at 1,000ft intervals.

8) Once the string is below the SCSSV, increase the production rate to its normal level. 9) Break circulation when well above the last recorded hold up depth and establish a

Note: Monitor the pump pressure, wellhead pressure and coiled tubing string weight continuously throughout the operation. If there are any indications of problems pull back above the last hold up depth immediately and evaluate the situation.

1) Run in slowly to the top of the fill, stopping to note the hanging weight. Slow down when the weight begins to drop off the tubing and flag pipe at surface as a reference. The tubing must be kept in tension at all times.

2) After penetrating 20ft, pick-up to the tubing shoe then run back in to repeat the process in stages of 20ft, pumping continuously.

3) Having reached the required depth, continue to pump gel while reciprocating the tubing back to the tubing shoe twice. Carefully monitor fluctuations in pick-up weights. If an increase is seen, wash back until weight corresponds with the initial running weight.

4) Pull up above the perforations and displace the tubing to treated seawater.

5) Pull out with the well flowing to ensure that all sand moving up as the tubing is removed.

6) Rig down and hand control of the well back to Production.