Special liner design improves dual lateral horizontal well.

The use of multiple horizontal sections from a single vertical well bore has increased well potential and improved the economics of producing the Austin chalk. The vertically fractured Austin chalk formation in central Texas is difficult to drill from both technical and economic perspectives.

Torch Energy Advisers Inc. recently completed a unique northwest-southeast dual opposing lateral horizontal well, the Basclen No. 1-H, in the Austin chalk in Fayette County, Tex. (Fig. 1). The well has a 3 1/2-in. OD perforated liner run to total depth (TD) in the northwest lateral and a 2 7/8-in. OD perforated liner run to TD in the southeast lateral. Both laterals were cased off into a single 5 1/2-in. production string.

The Basden No. 1-H well plan hacl to overcome some of the drilling challenges inherent in the vertically fractured Austin chalk in the Fayette County area of the Giddings field, including the following:

* High bottom hole pressures

* Strong kicks that could deliver large volumes of oil and gas to the surface

* Harsh drilling fluids ([C.sub.a]CI.sub.2])

* High temperatures (270-280[degrees] bottom hole circulating temperature)

* Major faults with large geological throws

* Minimal distance between the base of the ash and top of the Eagleford shale. The combination of large throws and thin target zones required large true vertical depth (TVD) changes in well bore trajectory, yet little vertical section was available to accomplish the task.

Background

Torch drilled and completed its first re-entry Austin chalk horizontal well, the Appelt No. 2-H, in July 1990. The Appelt No. 2 well had originally been completed in the Edwards formation in October 1980, but the 4-1/2 in. production liner later collapsed at 10,500 ft. The well was subsequently plugged back to 9,900 ft, and a 42-ft section of 7-in. casing was milled from 9,800 to 9,842 ft.

The well was sidetracked at that point and deviated at a 20[degrees] inclination to the southwest until it reached 10,250 ft TVD. A medium-radius curve was then drilled with a 16[degrees]/100 ft deviation until the well reached an angle of 87 1/2[degrees] in a north-westerly direction.

The well was then horizontally drilled, with a 2,235-ft vertical section. The well tested with a potential of 657 …