Antelope-4 ST-1 Drilling Report

[johnwgrant]

With all of this delay they have obviously experienced some problems that have not been revealed to the public by either IOC or OSH (or Total).

Sept. 18 , 2015 IOC PR: “The Antelope-4 side track appraisal well in Petroleum Retention License 15 has intersected the reservoir 36 meters (118 feet) higher than the original Antelope-4 penetration.”

Sept. 30, 2015 OSH Drilling Report: “At 30 September 2015, Antelope 4 ST1 was at a depth of 1,940 metres and running liner in an 8- 1 /2” hole, after tagging the top of the target carbonate reservoir”.

Oct. 19, 2015 IOC PR: “The top of the reservoir had been encountered in the Antelope-4 ST-1 well at 1,875 meters (6,152 feet true vertical depth sub-sea), which was 36 meters (118 feet) higher than the original Antelope- 4 penetration. Casing has been set above the reservoir and cement bond logs recorded. Prior to drilling ahead additional cementing operations are being conducted to ensure integrity of the casing shoe...”

Oct. 31, 2015 OSH Drilling Report: “At 31 October 2015, Antelope 4 ST1 was at a depth of 1,950 metres and running 5” liner in an 8- 1 /2” hole, after tagging the top of the target carbonate reservoir approximately 30 metres high to expectations”

On Sept, 30, 2015 they were running a liner at a depth of 1,940 meters in an 8 ½” hole.  They did not say what size liner they were running but I assume it was a 7” liner. On Oct. 19th, 2015 they had casing set “above the reservoir” but they do not say how far above the reservoir. This at least implies that the liner was set at the top of the reservoir or at about 1,940 meters drill depth (or 1,875 meters sub sea).

On Oct. 31st they are again running a liner (this time they tell us the size is 5”) in an 8 ½” hole at a  drill depth of 1,950 meters or almost the same as the previously reported 1,940 meters. I believe the 1,940 meters is an error and the 8 ½” hole has always been at a depth of 1,950 meters drill depth. (It is highly unlikely that they drilled an additional 10 meters of 8 ½” hole below the 7” liner)

It is very uncommon to set two liners at the same depth. Two reasons come to mind:

1. The 7” casing got stuck before it reached bottom and could not be pulled back out. I discount this possibility because they have told us the first liner was set “above the reservoir and cement bond logs recorded.”

2. They have perforated the 7” liner in many places to squeeze cement behind the casing to improve the cement bonding. After squeezing cement through the perforations the casing will normally hold pressure and can be trusted so that we could drill ahead safely. I think the casing has either failed the pressure test or Total does not want to trust the 7” liner to hold pressure because of the perforations or possibly a hole in the liner. So before drilling ahead they have decided to run the 5” liner inside the 7” liner at more or less the same depth to give them an additional layer of steel for safety before drilling ahead.

Unfortunately with the 5” liner in place we will only be able to drill ahead with a bit size of about 4”.  We should be able to drill through the reservoir, log and test. The hole is pretty small for side wall cores but they could take some full hole cores it they decide that is required although coring equipment for a hole this small is probably not available locally. They probably will not case the reservoir section because they would have to use something like 2 7/8” tubing as casing for this 4” hole.

OSH is now stating that the planned TD is 2,375 metres. They had previously sated the planned TD was 2,468 metres. So using their latest number we have an additional (2,375 -1,950) 425 meters or 1,394 feet to drill. Part of the delay was probably having to bring in the 5” liner and now they will need enough smaller drill pipe and drill collars to drill this additional 1,394 feet of hole.

We have now been at this depth for at least 7 weeks and it has been nearly 10 weeks since they started operations at Antelope-4 ST-1.

As per the above, initial planned TD was 2,468 meters -->then 2,375 meters --> and now 2,262 meters (actual per today's report).      This 2,262 meters is 48 meters BELOW the gas/water contact.      My question is this:   have we not already drilled this reservoir enough times to know where the gas/water contact is?      Does the gas/water contact have a slope - ie, move up or down with distance from the previous well.      Just a puzzlement to me !

[petrengr1]

With all of this delay they have obviously experienced some problems that have not been revealed to the public by either IOC or OSH (or Total).

Sept. 18 , 2015 IOC PR: “The Antelope-4 side track appraisal well in Petroleum Retention License 15 has intersected the reservoir 36 meters (118 feet) higher than the original Antelope-4 penetration.”

Sept. 30, 2015 OSH Drilling Report: “At 30 September 2015, Antelope 4 ST1 was at a depth of 1,940 metres and running liner in an 8- 1 /2” hole, after tagging the top of the target carbonate reservoir”.

Oct. 19, 2015 IOC PR: “The top of the reservoir had been encountered in the Antelope-4 ST-1 well at 1,875 meters (6,152 feet true vertical depth sub-sea), which was 36 meters (118 feet) higher than the original Antelope- 4 penetration. Casing has been set above the reservoir and cement bond logs recorded. Prior to drilling ahead additional cementing operations are being conducted to ensure integrity of the casing shoe...”

Oct. 31, 2015 OSH Drilling Report: “At 31 October 2015, Antelope 4 ST1 was at a depth of 1,950 metres and running 5” liner in an 8- 1 /2” hole, after tagging the top of the target carbonate reservoir approximately 30 metres high to expectations”

On Sept, 30, 2015 they were running a liner at a depth of 1,940 meters in an 8 ½” hole.  They did not say what size liner they were running but I assume it was a 7” liner. On Oct. 19th, 2015 they had casing set “above the reservoir” but they do not say how far above the reservoir. This at least implies that the liner was set at the top of the reservoir or at about 1,940 meters drill depth (or 1,875 meters sub sea).

On Oct. 31st they are again running a liner (this time they tell us the size is 5”) in an 8 ½” hole at a  drill depth of 1,950 meters or almost the same as the previously reported 1,940 meters. I believe the 1,940 meters is an error and the 8 ½” hole has always been at a depth of 1,950 meters drill depth. (It is highly unlikely that they drilled an additional 10 meters of 8 ½” hole below the 7” liner)

It is very uncommon to set two liners at the same depth. Two reasons come to mind:

1. The 7” casing got stuck before it reached bottom and could not be pulled back out. I discount this possibility because they have told us the first liner was set “above the reservoir and cement bond logs recorded.”

2. They have perforated the 7” liner in many places to squeeze cement behind the casing to improve the cement bonding. After squeezing cement through the perforations the casing will normally hold pressure and can be trusted so that we could drill ahead safely. I think the casing has either failed the pressure test or Total does not want to trust the 7” liner to hold pressure because of the perforations or possibly a hole in the liner. So before drilling ahead they have decided to run the 5” liner inside the 7” liner at more or less the same depth to give them an additional layer of steel for safety before drilling ahead.

Unfortunately with the 5” liner in place we will only be able to drill ahead with a bit size of about 4”.  We should be able to drill through the reservoir, log and test. The hole is pretty small for side wall cores but they could take some full hole cores it they decide that is required although coring equipment for a hole this small is probably not available locally. They probably will not case the reservoir section because they would have to use something like 2 7/8” tubing as casing for this 4” hole.

OSH is now stating that the planned TD is 2,375 metres. They had previously sated the planned TD was 2,468 metres. So using their latest number we have an additional (2,375 -1,950) 425 meters or 1,394 feet to drill. Part of the delay was probably having to bring in the 5” liner and now they will need enough smaller drill pipe and drill collars to drill this additional 1,394 feet of hole.

We have now been at this depth for at least 7 weeks and it has been nearly 10 weeks since they started operations at Antelope-4 ST-1.

As per the above, initial planned TD was 2,468 meters -->then 2,375 meters --> and now 2,262 meters (actual per today's report).      This 2,262 meters is 48 meters BELOW the gas/water contact.      My question is this:   have we not already drilled this reservoir enough times to know where the gas/water contact is?      Does the gas/water contact have a slope - ie, move up or down with distance from the previous well.      Just a puzzlement to me !

John- It is a little confusing but the numbers from Oil Search are drill depth numbers but the new number in today's presentation is TVDSS (true vertical depth sub sea). So to make the numbers comparable we have to add the derrick elevation to today's number (2,262 +78) plus 8 or 10 meters for the additional length of the deviated hole or +/- 2,350 meters drill depth. So, yes they did stop short of the Oil Search number of 2,375 meters drill depth but not too much. They needed to confirm the depth of the gas/water contact and in order to do this they have to have room for the logging tools to go below the gas/water contact far enough to get a log across the gas/water contact.

Hope this helps a little with your frustration.