Troika Field: A Well Failure, and Then a Successful Workover

摘要

The second phase of Troika field development began in 2000. Two wells were planned to develop reservoirs adjacent to the primary Troika reservoir. The planned wells were deep, single zone, frac packed, subsea completions. The first of these wells was the Green Canyon Block 201 TA-6 ST#1 Well (TA-6). It was planned to have a well angle exceeding 40°, 7” production liner and 4” base pipe prepacked screens. After drilling the well, open hole logs showed the target reservoir was approximately 170 ft. thick, but there were two significant shale breaks within the reservoir. During completion, there were problems getting the 7” liner to bottom, so a 5-1/2” liner was run. The 5-1/2” liner was cemented in place, and then squeezed due to possible channels across the completion interval. The well was perforated and a 2-7/8” reduced diameter prepacked screen was run without difficulty. During the frac packing process, TA-6 did not have a live annulus, so circulating in this small casing was not possible. In addition, the crossover tool failed during pumping operations. This resulted in frac sand and gel plugging the wash pipe. Consequently, the pressure gauges could not indicate whether a good frac pack was achieved. TA-6 started production in November 2000 and produced 3.91 million barrels of oil and 4.48 billion cubic feet of gas with water cut slowly increasing to approximately 10% before a gravel pack failure occurred in January 2002. The well was cleaned out and a 1.3” diameter through tubing screen insert was run inside the failed screen. No attempt was made to place gravel pack sand between the screen insert and the failed screen. Since the screen nsert was installed, TA-6 has produced over 1.95 million barrels of oil and 2.7 billion cubic feet of gas with water cut less than 3%. This paper will evaluate this well’s history using BP’s new maximum flux guidelines1. In addition, it will use a new erosion model to evaluate both the probable cause of the well’s failure and the operating conditions of the successful workov er completion.