Topic: Drilling question — shareholdersunite.com

Drilling question

This topic has 6 voices, contains 15 replies, and was last updated by petrengr1 94 days ago.

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February 7, 2012 at 1:16 pm #7246
Libtardius Maximus	Does anyone know the trap formation and rock type over the T2 reef? and… What markers would mud engineers be looking for upon approach?
February 7, 2012 at 2:51 pm #7247
petrengr1	The Miocene age Puri Limestone is sealed by the Pliocene age Orubadi shale. They expect to see an intra-Orubadi sandstone at about 950 meters (+/- 150 m) or 3117 feet as shown on http://www.interoil.com/presentation/2011-11-15_3Q11_Results_Presentation_Final.pdf chart 15. The sandstone will have Orubadi shale above and below it. Primarily they will just be looking for the drill cuttings to change from shale to limestone to identify the top of the Puri limestone (hopefully reef) pay zone.
February 7, 2012 at 2:53 pm #7248
admin	They might also notice the drilling speed. That Orubadi shale can slow things to a crawl..
February 7, 2012 at 8:49 pm #7252
petrengr1	STP- I think you may be remembering some stories about there being a “marl” right above the Puri Limestone that is hard to drill through. In general, shales are not that hard to drill through. Shales can vary from soft to medium to hard. Sometimes shales can cause a lot of problems in getting the hole drilled but the problem is usually with hole stability not penetrating the shale with the drill bit. There are swelling shales, heaving shales and sloughing shales all of which tend to close the hole after you have it drilled. Sometimes these shales will even stick the drill pipe. But all of that is a story for another time. This marl is a shale with an increasing calcium carbonate content as the formation transitions from shale to limestone (calcium carbonate). I think such a transition zone is more likely to occur above a platform limestone than it is above a limestone reef. When the shale has an increasing carbonate content it is probably harder to drill through. So, if the marl is present, they will probably see a reduction in penetration rate near the top of the limestone but before drilling into 100% limestone. At Elk-1 there was a marl above the Puri limestone. You can see a picture of it on several sides here http://www.interoil.com/presentation/Elk_-_1_Update_Final_23Aug06.pdf . At Elk-4 the marl was absent. I think their theory is that the marl is above a limestone platform but it is absent above a reef. So I guess we will hope it is not present at Triceratops-2. It was present at Triceratops-1. Here is an excerpt from the Triceratops-1 drilling report: “Drilled 8 1/2 inch hole to 5,437 feet (1,657 meters). Seven inch casing was run to 5,437 feet (1,657 meters) and cemented. Evidence of the Orbulina Marl formation was first seen at approximately 5,250 feet (1,600 meters) with Calcium Carbonate (CaCO3) increasing from approximately 20% up to 60%. Geology as anticipated.” The presence of a marl is not a sure thing but is something they will be watching for that may give them an indication that they are approaching the top of the limestone or reef. I have been unable to find information about the presence or absence of the marl at Antelope-1 and Antelope-2. So, it is possible that there will be a marl above the Puri limestone at Triceratops-2 but I hope it is missing which may be an indication that the limestone is a reef. Before they get to this point I believe they will stop drilling and set an intermediate string of casing- probably 13 3/8”. They are presently drilling with a 17 ½” bit. After setting the 13 3/8” casing they will drill ahead with a 12 ¼” bit to the top of the reef.
February 7, 2012 at 9:19 pm #7254
admin	Thanks for that exposé, Petengr. We always learn something new. I heard a story years later about how the shale slowed down drilling to a crawl (to the tune of a few meters a day), I don’t remember which well, but probably one of the Elk wells, as it’s quite some time ago.
February 13, 2012 at 1:01 pm #7517
ebster123	Pet, or others if you know, I know the data was posted but I can’t seem to find it in the posts. Given the distance per day drilled and the distance needed to hit gas and the spud date when should they hit the desired drill depth for reserves? Thanks
February 13, 2012 at 1:03 pm #7518
petrengr1	OK, due to boredom I have decided to do the impossible. Predict the future knowing it will be wrong before I write it. Since I know nothing I will have to make some assumptions. I will assume the casing sizes will be the same as the last well drilled i.e. Antelope-2. At Antelope-2 it took them 28 days to get the 13 3/8” casing set at 3612 feet. I will assume they will set the 13 3/8” casing at 3100 feet at Triceratops. They should be able to do that in 25 days. Spud date was Jan. 17th and, after 16 days, they were drilling ahead at 1693 feet. They should have the 13 3/8” casing set by Feb. 11th. At Antelope-2 it took 46 days from the time they set 13 3/8” casing until they were ready to drill out below the 9 5/8” casing. That means they had drilled to the top of the zone, run and cemented the 9 5/8” liner and run the 9 5/8” tie back from the top of the liner to the surface with the dual down-hole deployment valves. I will assume it took them a week to do all of the casing work so they should have reached the top of the zone at 6007 about 39 days after drilling out below the 13 3/8” casing. That means they drilled about 2400 feet of 12 ¼” hole in 39 days or about 61 feet/day. This formation is a little deeper and possibly a little harder than the more shallow T-2. At Triceratops-2 the top of the zone is expected to be at 4330 feet. So based on my other assumptions they will need to drill about 1230 feet below the 13 3/8” casing to reach the top of the reservoir. This section drilled at 167 feet/day at T-1 with an 8 ½” bit. We will be using a 12 !/4” bit at T-2 so let’s estimated a penetration rate of 100 feet/day or 10 days to reach the top of the reef. This should put them at the top of the reef on about Feb. 21st. They should be drilling the reservoir sometime around Feb. 27th after running and cementing the 9 5/8” liner and the tieback with the DDV’s. We will have to wait and see if they do any coring, logging and testing prior to reaching TD. I expect them to start coring as soon as they confirm the presence of the reef. All of the above is just a wild guess and assumes no mechanical problems or delays waiting on equipment etc.
February 13, 2012 at 1:59 pm #7521
ebster123	Just what I was looking for, thanks Pet!!!
February 13, 2012 at 2:35 pm #7525
Palmtok	Thanks pet! Question, since you’ve mentioned it before. You had said at one time that with this formation being so much shallower, it will be higher pressure and they will be guarding against kicks, assuming we have reef there. Does the above take into account any steps they take to minimize/avoid dangerous kicks? And, or course should they experience some major kicks, what could occur that might really make a difference resulting in a major slow-down, or worse cause them to have to abandon this bore?
February 13, 2012 at 3:31 pm #7529
efi426hemi	“OK, due to boredom I have decided to do the impossible.” LOL, I wonder if that was what Einstein said??
February 13, 2012 at 3:58 pm #7531
petrengr1	Palm- In my paranoid mind the worst thing that could happen would be to have a shallow string of casing set somewhere at 400-800 feet and drill into a sand at 3100 feet that was severely over pressured. If we get a kick from an overpressured zone where the shallow casing seat will not hold the pressure, the well will blow out on the outside of the casing. It will be much worse than having to abandoned the well. I saw one happen like this once. Over a period of a couple of days the derrick fell over and the substructure and well bore disappeared into the earth. A crater formed followed by a small lake. Let’s hope this does not happen. IOC is aware of the possibility that both the upper sand and the top of the reef may be overpressured. I believe they think the sand is not over pressured but they know the reef is over pressured. So they will have taken the necessary precautions. I think we will have the intermediate casing set at least as deep as 2500 feet (I am hoping for 3100 feet) before drilling into the reef. Hopefully the upper sand will not be a problem or they will set casing before it is penetrated. The intermediate casing will protect us from the pressure in the reef and I expect them to set casing above the reef and have the dual downhole deployment valve in place before the start drilling the reef. I do not expect any problems that they will be unable to handle.
February 13, 2012 at 4:06 pm #7532
petrengr1	Palm-Check your yahoo mail box.
February 13, 2012 at 4:20 pm #7533
petrengr1	Palm-I sent you an email but I now see it was an incorrect address.
February 13, 2012 at 4:22 pm #7534
Palmtok	Pet, great explanation once again, and thanks for the reassurance. On email, I had to change it early last year as Yahoo told me there was “suspicious activity:, which I still get now if I send/receive a lot in a short period. Last year before knowing what I know now I had them shut the old one down and started a new one. Now I know that if you wait a day or 2 it usually clears, or if you want to clear it up immediately you can change your password. If STP would be so kind (since he is the keeper of the email addresses), I would ask that he email you my new address, so you can re-send. Thanks in advance STP.
February 14, 2012 at 10:38 am #7553
Libtardius Maximus	Pet, In one of the last two wells drilled, they lost circualtion up hole for a few days and had a heck of a time getting it back. Do you happen to remember which well and approx where in the hole it happened?
February 14, 2012 at 10:46 am #7555
petrengr1	Sorry Lib, I don’t remember that. The only lost circulation prolems that I remember occurred after they drilled into the reef or fractured limestone.