James R. Wible
Aran Energy Corp.
Houston
Cutting a window at 850 deviation allowed a sidetrack to pass through the high-resistivity sections in a Gulf of Mexico reservoir.
Results from logging-while drilling (LWD) tools indicated the original horizontal bore dropped too low in the reservoir, possibly leading to a low productivity well.
The subsequent sidetrack successfully delivered the desired well bore, and the increased productivity justified the efforts in cutting a window in the horizontal section.
Aran Energy Corp's A 16 well in South Pass Block 37 was to be drilled as a horizontal test of the 2,600 ft sand. The plans were to set 9N in. casing at an inclination of 870 in the top of the sand. An 8-in. hole would then be drilled, and the inclination angle would be adjusted as required to take advantage of any "sweet spots" in the reservoir. Aran Energy planned to use LWD tools for formation evaluation and to help make trajectory correction decisions on site.
Problems in controlling the trajectory occurred immediately after the well was drilled out from the 9N in. casing shoe. Despite attempts to level the well course, the hole exited the bottom of the sand before the inclination reached 900. The angle was then brought up to more than 950 to regain a level position in the higher resistivity portion of the pay (Fig. 1).
Again, there was some difficulty in controlling the well course during attempts to flatten the trajectory. The well course continued up until the projected bottom location was above the top of the sand.
The inability to control the well course was attributed to the rigidity of the drilling assembly because of the use of a triple combo LWD tool. Two previous horizontal wells on this South Pass 37 platform had been drilled without the LWD tool and with no control problems in the horizontal section (OGJ, Sept. 27, 1993, p. 26).
After the well was drilled through the top of the sand, Aran had to decide if the well bore would meet its objectives or if another more desirable hole should be drilled. The log from the horizontal section indicated two intervals of high resistivity, but the desired length of pay had not been exposed. The operations personnel and the partners agreed that another hole could be drilled successfully, but the original hole would need to be plugged and a window cut in the 9N in. casing. Following a quick decision, the sidetrack operation began.
WINDOW CUTTING
Using drill pipe, a cement retainer was set in the 9N in. casing at 3,834 ft, and 150 sacks of cement were squeezed below. A whipstock packer, also run on drill pipe, was then set at 5,827 ft. Single shot surveys were then taken to determine and confirm the orientation of the setting lug in the packer.
The whipstock was adjusted to sit 450 to the left of high side. Coming out high side offered more flexibility for future operations; the rotation of the drill pipe would force the cuts to the right (or in the direction of high side).
The whipstock was run in the hole, stabbed into the packer, and sheared without incident. The top of the whipstock was at 5,815 ft. The starting mill cut from 5,815 to 5,818 ft in 5 hr of milling. The pipe was then tripped out of the hole.
On the next run, 8 in. window and watermelon mills elongated the window from 5,818 to 5,827 ft and drilled hole from 3,827 to 5,847 ft (3 hr milling and 2 hr drilling). A string mill was then run with the watermelon mill to elongate the window from 5,778 to 5,818 ft (2 hr drilling and washing). The assembly was washed to bottom and then pulled out of the hole.
Directional drilling operations resumed, and the horizontal section was drilled to take advantage of two distinct, vertically separated zones of high resistivity.
After the well reached total depth, an 8 in. hole-opener run was made without incident. Some difficulty was encountered in running the 7 in. liner through the window. The liner was pulled, and the window was elongated an additional 4 ft. The liner was then run through the window without difficulty.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
