Newly developed screen resistant to corrosive environment
BP Exploration (BPX) of Houston has successfully completed a concentric screen horizontal workover in the US Gulf of Mexico at Viosca Knoll 989 A-10 (Pompano) utilizing a 2-7/8-in. multilayered composite metal screen (Pall Stratapac) run inside a failed dual-screen prepack.
The horizontal section was drilled at 3/100 ft to an average hole angle of 87 (maximum angle of 93). The 2,600 ft open hole pay zone was drilled to a true vertical depth of 7,000 ft with an estimate bottomhole pressure of 2,500 psi.
The well was initially completed with 1,605 ft of dual prepack 20/40 resin-consolidated sand (7.11-in. OD, 4.892-in. ID) spaced out in four sections, ranging from 440 ft to 660 ft separated by 62 ft of blankpipe. The screen jacket was mechanically coupled to the base pipe, which was constructed of 17# 13Cr-80. The wire-wrap screen was 0.008 gauge stainless steel.
The l3Cr-80 base pipe was chosen for its corrosion resistance against moderately high C02 at 125 F. To protect against formation overburden collapse, the screen was built on 80,000 lb yield base pipe, instead of the more common 30,000 lb yield pipe.
Production began in April, 1995. Typical production flow was about 3,000 b/d with 10% water cut. The well had produced about four months before the onset of sand production. Based on post-failure analysis of other horizontal wells, it was initially suspected that the well failed due to screen collapse.
However, after washing out sand bridges a full drift using a 4.500-in. bit failed to reveal any blockage. Therefore, BP suspects that the well may have failed due to erosion of the screen. A spinner analysis of a similar well revealed anomalies in the production log indicating that localized zones of high production can occur along the length of horizontal completions.
A high velocity zone could have eroded the screen, or alternatively, the screen could have been damaged during installation, creating a preferential flow path through the resin-bonded prepack.
This screen, manufactured by Pall Corporation, replaced a prepack that failed prematurely in a US Gulf well.
The workover was performed in August, 1993. Sand was washed out of the screens and blank pipe to total depth with 3% KCl using coiled tubing. A 20 bbl high viscosity pill was used to sweep out residual fines in the screen basepipe. The well was killed and the production tubing and accessories were pulled from the wellbore while closely monitoring the tubing, nipples, gaslift mandrels, downhole safety valves, and production seals.
A specific volume of 10 ppg saturated NaCl brine was made up for open hole washing operations. Washing operations were performed with 2,730 ft of 2-7/8-in. PH-6 work string with a 4.500-in. bit run to bottom, displacing residual salt pills and sand. Returns were carefully monitored.
After washing, the work string was pulled above the packer and the well was displaced with a 8.4 ppg brine. An attempt to identify the screen failure was performed by running a gravel pack log on coiled tubing. The log was inconclusive.
A total of 1,485 ft of 2-7/8-in. Stratapac Screen (3.44-in. OD, 2.44-in. ID) with Hydril 563 connections supplied by Pall Well Technology were run inside the failed screen. A 6.4# N80 base pipe was chosen as a less expensive alternative to 13Cr-80 because the Stratapac Screen was non-loadbearing and could tolerate greater corrosion loss to the base pipe than that of the dual prepack screen. The 316L filtration material in the Stratapac Screen has an excellent corrosion rating over the projected life of the well.
A 4.5# 2-1/16-in. CS Hydril 511 wash pipe assembly was simultaneously made up inside the Stratapac Screen and the total assembly was run in on 5-in. drill pipe. The screen sections were evenly alternated with an equal amount of blank pipe, and the assembly was positioned across the original screen interval. The all-metal screen design was chosen over other designs because of it's damage-tolerant construction and high in-flow area.
After production tubing installation, a 1-1/4-in. coiled tubing unit was rigged up to flush tubing lines and the 1-1/4-in. blowout preventers. After the volume in the coiled tubing unit was displaced with completion fluid, it was run to total depth and the screens were acidized with 7.5% HCl acid and additives.
The acid was displaced with 3% KCL. Production was initiated by jetting the well above the downhole safety valve with nitrogen until the well flowed at 750 b/d. Production was slowly increased to 1,500 b/d through a 30/64 choke. After ten days, the choke was opened further and the well produced 2,100 b/d with an initial drawdown of 500 psi.
Low initial production was important to provide uniform flow around the workover screen. The total cost of workover was about US$1.5 million, which was paid out in three months. After 196 days of operation, the total production stood at 320,475 bbl oil and 9,808 bbl of water.
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