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Some well interpretation from IOC’s Antelope2 first DST test

October 14th, 2009 · 2 Comments

The specialist post by this person are collector’s items..
Comments on DST No.1 and PR

The primary purpose of DST No. 1 was to prove that the Antelope Reef extended 2.3 miles from the Antelope 1 well. This has now been conclusively accomplished. The well produced a very significant amount of gas at 14.1 MMCFD. The liquid content, at 16.5 barrels/MMCF, was also significantly better than previous tests in other wells where the liquids were reported to be between 5 and 13 barrels/MMCF. This higher liquid recovery may be due to better testing methods or because of the pressure drop being taken at two spots i.e. at the bottom of the hole and at the surface. Of course the zone being tested is also slightly lower (about 300 feet) than the top of the zone at Antelope 1. The test interval (6011-6175 feet) was 164 feet or 50 meters. The most productive interval in Antelope 1 was in the top 30 meters of the hole so it is not surprising that they elected to stop and test the top 50 meters. It is common practice to use a bottom hole choke in the DST tools as a safety precaution. In this case I believe they had a ¾” bottom hole choke in the DST tools and a 35/64” choke at the surface. The 2070 psi flowing tubing pressure is not a meaningful number due to the pressure drop across the bottom hole choke. The flowing tubing pressure would have been much higher with no choke at the bottom. They will not be able to calculate the AOF (absolute open flow) until they recover the bottom hole pressure gages which are below the bottom hole choke. They will be able to analyze the pressure drawdown during the flow test and the pressure buildup after the well was shut-in, probably at the bottom hole test tool. This test in no way should be considered to reflect the actual capability of the Antelope 2 well since the flow was restricted by two chokes and the pipe size utilized for the test.

The coring operation was highly successful in that they cored from 6057-6175 feet (118 feet) and recovered 117.5 feet, only losing 6 inches out of the 118 feet. This is excellent core recovery. The core is described as having very good visible porosity and vugs from the reefal reservoir. They did not say so but I assume this is all dolomite. It will be sometime until they get the actual core analysis from the lab. This core information will be very beneficial (valuable) in evaluating the gas reserves at Antelope Field. Actual core porosity is better information than the data obtained from logs.

Tags: IOC

2 responses so far ↓

  • 1 rory mcgowan // Oct 15, 2009 at 12:51 am

    ADMIN & PETG could you talk about what the pressure drop means? I wasn’t expecting that. thanks in advance

  • 2 Darcy Patten // Oct 15, 2009 at 1:28 am

    Rory, I think the pressure drop that Pet is referring to can be explained from the following:

    “It is common practice to use a bottom hole choke in the DST tools as a safety precaution. In this case I believe they had a ¾” bottom hole choke in the DST tools and a 35/64” choke at the surface.”

    and

    “The 2070 psi flowing tubing pressure is not a meaningful number due to the pressure drop across the bottom hole choke. The flowing tubing pressure would have been much higher with no choke at the bottom.”

    So what I think the pressure drop means is that the bottom hole choke is only allowing a fraction of the NG through meaning a pressure drop as opposed to NG flowing with no restrictions.

    And it would appear that Pet is suggesting that there are 2 chokes in place, one near the bottom of the hole and one at the surface. Sooo, that should mean the pressure would be significantly reduced at the surface.

    But I am no Petro Engineer, so someone please correct me if I am out to lunch here.