BP Exploration has finished the North Sea's second horizontal well drilled by a semisubmersible rig.
Site is in Cyrus field in U.K.
North Sea Block 16/28, where BP drilled the sea's first horizontal well in summer 1988 in about 110 m of water (OGJ, Sept. 5, 1988, p. 28).
The two wells eventually will produce Cyrus's 13 million bbl reservoir using the Seillean oil production vessel (OGJ, Oct. 2, 1989, p. 44).
The company did not disclose a gauge for the latest well. The first well flowed at a rate of about 6,000 b/d through a 1 in. choke.
The second horizontal well in Cyrus had to be spudded exactly 9.75 m from the first well to be in reach of the production vessel's common manifold for simultaneous production.
Drilling the well required great accuracy to meet production requirements. BP made extensive use of a drill string simulator the company recently developed (OGJ, Aug. 28, 1989, p. 41).
Meanwhile, Seillean has completed sea trials, including operations with a dummy subsea wellhead. It is at Invergordon north of Aberdeen, Scotland, in final outfitting.
The vessel, designed to produce multiple small or remote reservoirs, will depart in late January. It can accommodate 16,500 b/d of produced fluids and has 300,000 bbl of storage capacity.
Its first assignment will be either Cyrus field or the northwest lobe of Forties field, an extension that cannot be reached from any of Forties' five drilling and production platforms.
DRILLING PROGRAM
Spudding the second horizontal well Sept. 1, 1989, BP drilled vertically to about 1,500 m true vertical depth subsea (TVDss) before deviating a 12 1/2 in. hole 55 from vertical.
It drilled that deviated hole through the reservoir into underlying rocks and left the well bore open 30 days for intensive logging. Logs accurately located the top and bottom of the Paleocene Andrew formation.
BP then plugged back to just above the reservoir, resumed drilling to build angle, and set 9 5/8 in. casing Oct. 13 at 2,559 m TVDss. Technically, the setting of 9 5/8 in. casing with the shoe at 820 was a sidetrack.
The company drilled 884 m of hole beyond the casing shoe, including 825 m of horizontal section, into the reservoir. Total drilled depth is 3,800 m below rotary table.
The horizontal section is parallel to and 12 m above the oil/water contact, which is at 2,580 m TVDss.
BP achieved a vertical tolerance of 3 m on the horizontal well path. Minimum length of the horizontal section was to be 700 m.
The company used measurement while drilling tools and a steerable downhole motor for the entire well.
The drillstring simulator was extensively used for control and steering. The simulator proved to be valuable in predicting performance because the well behaved differently from the first horizontal well in the field.
The horizontal section in the first well is about 16 m above the oil/water contact.
The difference in the position of the horizontal section between the two wells resulted from the more accurate reservoir information that emerged from the detailed logging that took place.
BP drilled the well using the company owned Sea Explorer, which has undergone upgrading. The company said the upgraded mud circulation system assisted drilling performance.
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