SPECIAL LINER DESIGN IMPROVES DUAL LATERAL HORIZONTAL WELL

Gordon Talk
Torch Energy Advisers Inc.
Houston

Steve Wooten
Steve Wooten Consulting Services
College Station, Tex.

Derrick Lewis
Smith International Inc.
Houston

Todd Talbot
Baker Service Tools
Houston

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 Basden 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 had 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 (CaC12)
High temperatures (270-280 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 inclination to the southwest until it reached 10,250 ft TVD. A medium-radius curve was then drilled with a 16/100 ft deviation until the well reached an angle of 87 1/2 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 bo/d and 2,300 Mcfd of gas on a 28/64-in. choke with 3,650 psi flowing tubing head pressure (FTP). To date, this well has produced in excess of 100,000 bbl of oil and 645,000 Mcf of gas and recently tested at 126 bo/d and 750 Mcfd on a 24/64 in. choke with 430 psi FTP.

Because of the successful drilling and producing experiences on the Appelt No. 2-H, Torch began a development drilling program in the Austin chalk on the Appelt and surrounding leases; the independent operator has drilled and completed 11 horizontal wells in the area and has plans for several additional horizontal wells.

Torch has also begun running a perforated liner in the horizontal section of each Austin chalk completion. The liner ensures that the entire lateral section will remain open for production for the life of the well, and the liner can allow accurate fracture stimulation by coiled tubing if necessary.

Since the loss of the horizontal section (because of the collapse of ash and shale) on the Appelt No. 2 and the subsequent liner policy, all 11 horizontal wells completed with a perforated liner have remained open. None has required stimulation.

WELL PLAN

An examination of the drilling unit and seismic data revealed that the Basden No. 1-H was an excellent candidate for a dual horizontal lateral well. The seismic data indicated a series of faults in stair-step fashion along the planned path of the dual lateral. The drilling unit was situated such that either a single lateral of 5,200 ft or a dual lateral of 2,600 ft for each leg could be drilled (Figs. 2-3).

After an analysis of drilling costs and difficulties for each option, the dual lateral well was chosen. Because of the potential for collapsing ash and shale in the Austin chalk, Torch decided to run liners in both laterals.

The well plan called for a 3 1/2-in. liner for the updip lateral. This liner would then be crossed over to a 5 1/2 in. liner hanger section. The 5 1/2-in. liner hanger section would have a 10-ft window cut in it, which would be aligned with the downdip lateral at the kickoff point.

This configuration would allow the second liner, 2 7/8 in. OD, to pass through the 5 1/2-in. liner section and then through the window into the downdip lateral. The 2 7/8 in. liner would land on a 2 7/8 in. x 7-in. packer.

Orientation subs would be placed one joint from bottom on each liner. The subs would enable the directional and drilling personnel to ensure that each liner was run in the correct lateral. The bottom joint on each liner would have a bend to ease the passing of the liner through the build portion of the lateral.

DRILLING

The Basden No. 1-H well was spudded on Mar. 1. After 16 in. conductor pipe was driven, a 14 3/4-in. hole was drilled to 3,200 ft. Then 10 3/4-in. surface casing was run, set, and cemented. A 9 7/8-in. hole was drilled to 9,840 ft, and 7-in. casing was run and set without problems.

After the float equipment and 40 ft of formation were drilled out with a 6 1/8-in. bit, a Dyna-Drill positive displacement motor (PDM) designed for straight hole drilling was picked up and used to drill to 10,016 ft measured depth (MD). The motor was run primarily to improve the rate of penetration (ROP), which increased from 6 to 15 ft/hr. A 6 1/8-in. hole was maintained from intermediate casing point to TD in each lateral.

The updip (northwest) lateral was drilled first because the normal directional drift in most vertical wells in this region is to the northwest. Generally, 3-5 of inclination to the northwest quadrant can be expected by the time the bit reaches the Austin chalk. An inclination of 5 would be enough angle to allow a low-side open hole sidetrack of the downdip (southeast) lateral without having to use much of the updip curve. Therefore, the build rate would not have to be as aggressive as if the sidetrack started at a deeper TVD.

UPDIP LATERAL

Because of the harsh drilling environment and high bottom hole temperature, the updip lateral leg was drilled with a hot-hole steering tool wet-connect system and a 4 3/4-in. double-bend, hot-hole motor capable of build rates of 15 18/100 ft.

The kickoff occurred at 10,016 ft with 5 of inclination. Drilling continued with the bottom hole assembly building angle at 16.9/100 ft to 10,526 ft MD, where 92 was projected as the angle on bottom. A slick 4 3/4-in. steerable motor with a 1 1/4 bend then drilled the extension from 438 ft to 2,650 ft vertical section in 145 sliding and rotating hours.

From 438 ft to 1,850 ft, vertical section hole inclination of 92-95 was maintained. Beginning at 1,850 ft, a second build section was planned to hold an angle of 103 1/2. A 1 1/4 bend, slick steerable motor was run in sliding mode to increase the inclination. Build rates as high as 8 1/2/100 ft were achieved, and the well bore was built up to the second hold angle.

Because of the amount of faulting in the chalk, the well had to be drilled up through the ash and into the limestone. To reach the target, the well then crossed the fault and went below the ash.

The updip lateral leg reached the specified target at a total depth of 10,761 ft MD with a vertical section of 2,650 ft and 103.9 of inclination. Average ROP while sliding and rotating was 15.41 ft/hr, with real-time penetration rates of up to 70 ft/hr during drilling of the fault zones. The total rise in elevation was 252 ft TVD.

DOWNDIP LATERAL

After the drilling fluid in the updip lateral leg was conditioned, the drillstring was tripped out of the hole, and a double bend motor was picked up for the open hole sidetrack away from the original well bore. The sidetrack point was set at 10,007 ft, 9 ft above the original kickoff of the updip curve.

The northwesterly lateral drift in the vertical hole provided the necessary 5 of hole angle needed to orient the motor. After 7 hr of controlled drilling, a satisfactory ledge had been cut which was strong enough to allow drilling ahead with differential pressure. Differential pressure was slowly increased in stages until enough departure was achieved to determine that the sidetrack was successful. At this point, the southeast (downdip) curve was initiated.

This second curve was sidetracked and drilled with two motors. The original assembly fell behind the planned curve because of an abrupt decrease in build rates (from 17 to 14.9/100 ft), a result of drilling a productive interval midway through the curve.

At this critical point, build rates of 22-25/100 ft were required to reach the target at the base of the curve to prevent the well from entering the Eagleford shale. The drillstring was tripped out of the hole, and a more aggressive motor was picked up and run. This motor achieved build rates of 23.69/100 ft. The curve was completed at 10,565 ft MD, with 92.86 of hole angle projected on bottom and a 191-ft vertical section. The 92 or greater inclination projected on bottom was required to ensure that the well bore would not intersect the Eagleford shale, which was predicted to be only 4 ft below the actual well bore at 90 of inclination.

The 1 1/4 bend, slick steerable motor assembly used for the updip extension also drilled the downdip extension. This extension was drilled from 191 ft to 2,500 ft vertical section with an average hole angle of 87.3 (to approximately 1,900 ft vertical section). At this point, the hole angle was allowed to drop to 85 and was held there until TD was reached. This extension was drilled in 143 sliding and rotating hours with an average rate of penetration of 16.15 ft/hr and with a drop of 77 ft TVD.

Combining both updip and downdip laterals, the well had a net change in true vertical depth of 329 ft and horizontal extensions of 5,450 ft. The well was drilled in 288 sliding and rotating hours for an overall ROP of 15.7 ft/hr.

COMPLETION

After TD was reached in the downdip lateral, the steerable bottom hole assembly was pulled out of the hole and laid down. A 4 3/4-in. mill was installed on a bent joint of 3 1/2-in. drill pipe with an orientation sub run one joint above the mill. After the mill was lowered to the kickoff point at 10,007 ft, the bent joint was oriented to a northwest azimuth and slowly run into the updip lateral until it reached a deviation of 60. The hole was circulated clean while the mill rotated for approximately 90 ft to a deviation of approximately 82. Except for this interval, the mill was run to TD without encountering any additional fill.

After the updip lateral was circulated clean, the mill was pulled back to the kickoff point and oriented to a southeast azimuth and slowly lowered into the downdip lateral until it reached a deviation of 75. Again, the mill was rotated and the hole circulated clean for 30 ft to a deviation of approximately 80. The mill was subsequently run to TD without tagging any additional fill. After the downdip lateral was circulated clean, the mill was pulled out of the hole and laid down.

Prior to the running of the perforated liner, several liner design problems had to be considered: running each liner into the proper bore, orienting the window for the second liner, running the second liner through the window, and determining a contingency plan in case the liner orientation became slightly off.

The 3 1/2-in. perforated liner with the 5 1/2-in. liner section and liner hanger were run in the hole first (Fig. 4). The Hyflo II liner hanger was set with a hydraulic-release running tool. The bottom joint of the 3 1/2-in. liner was bent to approximately 6. After the base of the sidetrack was reached at 10,022 ft, the liner was oriented to align with the updip lateral and then run to 12,698 ft TD without problems.

The 5 1/2-in. liner window was then oriented to align the downdip lateral with the surface recording gyro. The liner hanger was set at 9,444 ft, and the liner was released. The drill pipe was then pulled out of the hole, and the 2 7/8-in. liner and 2 7/8-in. x 7-in. model FH packer assembly were picked up and run in to the top of the window at 10,012 ft. After the orientation and alignment were checked, the liner was lowered and slipped through the window into the downdip lateral (Fig. 5). The liner was run to 12,881 ft TD without problems.

The 2 7/8-in. x 7-in. packer was hydraulically set at 9,425 ft and then pressure tested to 1,000 psi with differential pressure. A wire line tubing plug was also run and set below the packer at 9,430 ft.

The drill pipe was released from the packer, and the 7 in. casing was displaced with completion fluid.

The 3 1/2-in. drill pipe was pulled and laid down, and 2 7/8-in. production tubing was run and hydrostatically tested to 5,000 psi going in the hole. The tubing was spaced out and landed with an on/off tool at 9,424 ft.

The Christmas tree was installed and tested hydrostatically to 5,000 psi. The tubing was then displaced with freshwater; tubing pressure increased to 3,000 psi, at which time the wire line tubing plug was pulled.

The well was then tied into a portable test unit and registered 2,200 psi shut-in tubing pressure. After the well cleaned up to the pit for 12 hr, a 24-hr potential test was run. The well tested at 2,750 bo/d, 3.3 MMcfd of gas, and 85 bw/d on a 32/64-in. choke with 2,300 psi FTP.

The Basden No. 1-H achieved all its objectives. The use of on-site geological evaluation and a team effort among the operator and the service companies were necessary for drilling this well in the challenging geological environment. Torch believes that the dual opposing laterals are a success, and that the technique is a viable method for drilling and completing wells in the Austin chalk.

ACKNOWLEDGMENT

The authors would like to thank personnel from Smith International Inc., Baker Service Tools, Big E Drilling Co., DMI, Multi-Shot Inc., Steve Wooten Consulting Services, and Petrograph Logging Services for their assistance in the preparation of this article.