Natural oil flow from the Upper Cretaceous Vivian sandstone far exceeded expectations at the Bretana Norte exploratory well in Peru, and Gran Tierra Energy Inc., Calgary, will drill a horizontal leg in the same formation.
Bretana Norte 95-2-1XD in the Maranon basin flowed at the rate of 1,170 b/d of 18.5° gravity oil, natural, for 19.65 hr without water on a 46/64-in. choke on a drillstem test of a 29-ft interval at 9,409-38 ft measured depth. With the choke opened to 64/64-in., the rate increased to 1,984 b/d, natural, for 1.5 hr, also without water.
Total recovery was 1,082 bbl of oil. Wellhead flowing pressure and temperature increased throughout the test, indicating that the formation was cleaning up, and oil flow rose for the duration of the test. The company ended the test when tanks were full.
Drilling of a horizontal leg in Vivian is to begin by the end of February, said Gran Tierra, operator of Block 95 with 100% working interest. The well has confirmed a 1974 heavy oil find (OGJ Online, Feb. 12, 2013).
The sidetrack will be completed and used to initiate a long-term test. When that test will start is uncertain but is expected to be within 12 months subject to facilities upgrade and execution of crude oil transportation and delivery agreements, Gran Tierra said.
Before the latest test, log interpretations and MDT fluid and pressure sampling had indicated the presence of an oil-bearing sandstone reservoir in the Vivian formation beginning at 9,408 ft MD, 8,851 ft true vertical depth, with an approximate gross oil column thickness of 99 ft and 53 ft net pay thickness.