CORING PROCEDURES 1. Operating Instructions

The following instructions apply to all sizes of core barrels.

Junk

On the last rock bit run prior to coring, ensure that the hole is free from junk, by running a junk sub in the assembly. If any doubt exists as to cleanliness of the hole, it may be advisable to run a reverse circulation basket or magnet, thus ensuring the complete removal of junk off bottom.

Tight hole

If it is known that hole problems (i.e. dog legs, tight spots, etc.) exist in the open hole, it is advised that the hole be well circulated and a wiper trip be carried out before coring. Care must be taken to avoid sticking of the core barrel in these problematic areas.

Core head selection

Make the core head selection based on previous experience, bit records and formation to be drilled.

Drill collars

Firstly, check the core barrel connections are compatible with the drill collars. If not, ensure a cross over is available.

Drilling practices dictate that sufficient collars are run to keep the drill pipe in tension and have sufficient weight to place on the bit. Similarly this practice is desirable whilst coring.

Stabilisation

As with diamond drilling, it is important that adequate stabilisation be run, keeping the core head steady on bottom, ultimately assisting bit life and core recovery.

The recommended assembly is, two drill collars, stabilisers etc. This should be strictly adhered to, as the core barrel will be the weakest point of the bottom hole assembly. If drill collar stabilisers are not run, premature failure of core barrel thread connections may occur.

Circulation

All core barrels are designed to run using various circulation mediums, i.e. air, water, drilling mud, with the variations that these materials may have.

The volume to be circulated will be determined by mud the type, diameter and depth of hole, pumps and formation. Once an average circulation rate has been established, variations of weight and rotary can be carried out. The flow can also be varied to achieve maximum cleaning and cooling of the core head.

Too low a flow rate can be detrimental as the cuttings will not be removed sufficiently quickly from the bit face, resulting in regrinding of the cuttings, slowed penetration rate and possible burning of core head. Too high a circulation rate will lift the bit off bottom resulting in diamond damage. There is also a possibility that loss of core can occur due to washing the core as it the enters bit throat. If this problem is suspected to be occurring when coring loosely consolidated formations, a face discharge bit run with a pilot type lower shoe should be applied. In these situations an emphasis should be made on cutting short cores, as the weight of the core in the inner tube should not exceed the formation strength of the material being cored, reducing again the possibility of breaking down of core and subsequent removal by washing.

Loss circulation material

Most core barrels can operate efficiently with LCM. However, care must be taken in the mixing of the material, to avoid large masses of material which could possibly block the core barrel or core head fluid water exhaust.

Rotary speed

When starting to core, a slow rotary speed of 40-50rpm should be applied. As the core enters the inner barrel and weight is added, the rotary can be increased. When carrying out a drill off test, the optimum rotary speed can be determined. Check critical drill pipe rotary speeds and avoid rotating in these areas. Through experience it has been found that a safe maximum rotary speed of 150rpm can be applied on core barrels, although in general a rotary speed between 70-120rpm is sufficient to core most formations.

Weight on core head

The weight run on the core head will be determined by the size of core head , size of core barrel and the nature of formation to be cored. When coring has commenced the minimum starting weight should be applied. Once core head has drilled a pattern and first stabiliser has entered the new hole, the weight can be increased in small increments (i.e. 2,000lbs) until optimum performance is achieved. Avoid exceeding the recommended maximum weight. Once a satisfactory weight has been reached, it should be maintained and not allowed to drill off.

Torque

Excessive or fluctuating torque should be avoided. Torque readings will change with varying formations or excessive weight and rotary speed. If high or fluctuating torque exists, find the correct combination of weight and rotary to achieve as smooth and as steady a torque reading as possible.

10.3.2. Preparing for Coring

1) Prior to pulling out of the hole for coring, make a short trip to the last casing shoe.

Return to bottom, circulate bottoms up and then pull out of the hole.

2) Ensure that there are no restrictions in the string to stop the passage of the pressure relief plug ball. If any doubt exists, a drift of the drill string shall be carried out to ensure the correct passage of the ball.

3) In full hole coring, tripping into the hole shall be methodical. Caution should be exercised at all tight places to prevent the core head from sticking. Tight places must be reamed out by rotating at maximum of 30rpm and using the maximum circulating rate and minimum weight.

Reaming of long intervals should be avoided with core heads, as their life can be adversely affected.

4) When the bottom is reached, make up the kelly and wash down to bottom taking a note of the pressure.

When a large amount of fill is encountered, it is advisable to clean to the bottom by circulating out the fill rather than coring it out. Use as little rotation as possible. Wash out slowly picking up periodically and checking kelly measurements with the pipe tally.

When the true bottom is reached a weight on bit gain accompanied by a pressure increase should be noted.

5) Once it is fully established that the bottom has been successfully reached, circulate for a further 10 to 15mins to clean out the inner barrel.

6) Pick up, break off the kelly and drop the steel ball. If necessary space out with pup joints in order to avoid (or minimise) pipe connection while coring.

7) Make up the kelly and pump the ball down at a good circulation rate (allow one minute per 1,000ft). When the ball reaches the pressure relief plug a slight pressure increase should be observed.

8) With the ball in place record the off bottom pressure at the same circulating rate that will be used during coring.

10.3.3. Starting of the Coring Operation

1) Check the pump strokes ensuring that the correct circulation rate is being delivered to the core head.

2) Lower the core barrel on to bottom and apply a weight of 5,000 to 7,000lbs (2 to 3t).

Start rotating, bringing the speed up slowly to 40-50 rpm.

3) When sure that core head has seated, (this should be apparent through pressure increase) maintain the starting weight until approximately one foot has been cored.

4) After cutting the 1ft (30cm) of core, the weight should then be increased in 2,000lbs increments. Increase the rotary speed to approximately 60 rpm. Once 2 or 3ft (0.5-1m) has been cored, the weight and rotary speed can be varied to achieve the maximum performance.

5) In general a rotary speed between 70 and 120 rpm is used to core most formations.

6) Slow rotary speeds are beneficial when coring fractured formations. Using speeds of 30 to 40 rpm produces less disturbance of the core.

7) The pump pressure should now have increased and levelled out. Therefore the pump strokes should be checked ensuring original flow rate is maintained. Take note of pressure and watch it constantly throughout the coring. Pump pressure increases or decreases are an indication that something abnormal is occurring and the cause should be determined and remedied. Make sure the flow rate has not changed due to a variation in SPM, pump malfunction or wash out in the string.

• If the pump pressure increase and the torque decreases, this generally indicates a formation change.

• If the pump pressure, penetration rate and torque decreases simultaneously, this indicates the barrel has jammed.

• If the pump pressure and torque increases simultaneously, the core head has probably ringed

8) The table 10.d shows flow rates given as a general guide only.

9) If situation is not corrected after a short time, the barrel should be pulled immediately to avoid excessive damage to core head, core barrel or loss of the core.

Hole Size (ins) Barrel Size (ins)

Table 10.D - Coring Flow Rate 10.3.4. Possible Cause Of Pump Pressure Changes

a) Pressure changes could possibly be due to changes in flow rate, debris in pump valve seats or washed liner. Check the pump strokes and condition of the pump first.

b) Pressure decreases could be attributed to the core jamming or filling of the barrel. This can occur in fractured or laminated formations, the core being jammed in the inner barrel or core catcher holding the bit off bottom, thus increasing flow area and causing a decrease in pump pressure.

However, in soft unconsolidated formations, it has been known for the pressure to increase, indicating that the formation being cored has jammed and is being drilled rather than cored and excess material is plugging the waterways of the core head.

Again in soft material the core may jam and no pressure charge be noted. However, the first instance is more likely.

Another possible cause could be a wash out in the drill string. In any of these cases it would be advisable to pull out of the hole.

c) Pressure increase, if the mud volume is constant, it is possible that the core head has

‘O’ ringed, i.e. the diamonds have been damaged letting the formation abrade the matrix, blocking off the fluid course and restricting fluid flow, therefore creating a pressure increase. An ‘O’ ring occurrence can be determined by picking up of the bottom, the pressure should then fall to normal off bottom pressure.

d) When re-tagging bottom, if the pressure increase is immediate, this confirms that core head damage has occurred.

e) Another possible cause for pressure increase could be the inner barrel or swivel assembly backing out and sitting on the core head. This can be determined by picking up off bottom, it is most likely in this case that the pressure will remain high. In either case the barrel should be pulled immediately.

f) Minor fluctuations in pressure could possibly be due to changes in formation, while mud is being mixed or unbalanced mud in the hole after a trip.

10.3.5. Breaking Core (Making A Connection Or Pulling Barrel)

When it becomes necessary to make a connection, or to pull a full core barrel, the following procedure should be followed:

1) Stop the rotary table and shut off the pump. Mark the kelly.

2) Pick up the drill string until the weight indicator shows the core spring has gripped the core. Continue picking up until core breaks or the recommended pull is reached. If the core does not break with the maximum strain, then start the pump at normal coring flow rate and hold the pull on the core until it breaks.

3) After the core has broken, raise the core head 10ft (3m) and then lower slowly back to within one foot of the bottom checking the weight indicator to see if there is any obstruction caused by core left in the hole.

4) If the core appears to be properly caught in the barrel, pick up and pull out of hole if coring is completed or make a connection if coring should be continued.

5) When coring is resumed after a connection, run to bottom without rotary or circulation and add weight approximately 50% higher than normal coring weight. This additional weight should release the core from the core spring, permitting the passage of new core into the inner barrel.

6) Pick up the drill string until the normal coring weight is reached. Start the pump at the normal rate. Bring the rotary speed up slowly to normal rotation and continue to core.

7) Make sure the pump pressures are normal when coring is recommenced.

10.3.6. Recovery of the Core

The following procedures cover the conventional inner tube. If other inner tube or rubber sleeve is used, the core recovery will be executed by a Coring Engineer.

When the core barrel is full or it becomes necessary to pull out of the hole, the following procedure should be followed:

1) Break the core and pull out of hole. When tripping, care should be taken when setting slips to avoid jarring the barrel as core loss may occur. It may also be advantageous to chain out the pipe whilst in open hole.

2) Special attention has to be paid during tripping in order to avoid pipe sticking.

3) If any drag occurs, rotate the pipe slowly with the slips in. Do not exceed 30,000lbs (15t) overpull.

4) The core shall be recovered under the Company Well Site Subsurface Geologist's supervision.

1) When the core barrel reaches surface place a collar clamp above the slips. Break off the last stand of collars and stand back in the derrick. Remove steel ball from the core barrel using the pick up tool. Make up an elevator sub, and torque up the sub using the tongs.

2) Pull the core barrel out of the rotary table. Break off the bit. Make up a core barrel protector making sure it is tight.

3) Run the core barrel back into the rotary table, a visual inspection of the core barrel and stabilisers can be carried out whilst the barrel is being lowered. Set the slips below the top stabilisers, replace the collar clamp.

4) Break out the safety joint, rotate out using chain tongs, and pull out the inner barrel.

Check the inner barrel connection has been pulled. Break off inner tube shoe lower half (catcher) using chain tongs or a pipe wrench. Place the core tong shoe on the inner barrel. The shoe should be backed out on the rig floor preventing core from falling out of the inner tube. Put the core tong handle on the core tong shoe. Exert pressure on the core tong handle and pick up the inner barrel slowly. Remove the inner tube shoe.

The core can now be removed from the inner barrel, as the inner tube is picked up.

When desired boxing length is reached, exert pressure on the core tong handle. The exposed core can then be removed and boxed. Lower the barrel, keeping pressure on the core tong handle until the core in the core tong is resting on the floor. The pressure on the core tong handle can now be released, pick up inner tube again exposing core.

This procedure should be continue until the core marker comes out of the inner tube. If however the core marker or further core does not appear, lower the inner tube onto the floor and knock the inner barrel with a sledge hammer until the core falls. Do not repeat the sledge hammer blows to the same area on the inner barrel as this will damage the tube.

If the core can not be removed in this manner it will be necessary to lay down the inner tube and pump out the core. Using the pump out bean and plunger, the core can be pumped out using water as a medium. Do not under any circumstances use pressurised air.

9) Once the removal of the core has been completed, clean off the catcher and lower shoe, replace if necessary. Make up the lower shoe up onto the inner barrel, tighten with chain tongs using cheater bars. Run the inner barrel back into the outer tube.

Check for bearing wear, if excessive change out. Check the ‘O’ rings. If all are in good condition, regrease the safety joint and make up to the recommended torque. Break off the protector. Evaluate the core head wear and change out if necessary.

10) Make up the core head. Pick up the barrel. Ensure the inner barrel is rotating freely, by placing a hand inside the core catcher and rotating. The barrel is now ready to run into the hole for further coring.

11) In case of continuous coring, ream with a drill bit at least every 100ft (27m) but only if a 8¹⁵/32" core head is used. With the use of a 8¹/2" core bit this operation is not necessary.

12) Reaming shall be avoided when using a core barrel. If this has to be done, use the maximum circulating rate with minimum weight and rotate at a maximum of 30rpm.

1) Refer to the Manufacturer’s field handbook for assembly of the core barrel and specific coring parameters.