The Bighorn No. 1-5: A 25,000-ft Precambrian Test in Central Wyoming
- J.C. Collins (BHP Petroleum (Americas) Inc.) | J.R. Graves (BHP Petroleum (Americas) Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- March 1989
- Document Type
- Journal Paper
- 13 - 16
- 1989. Society of Petroleum Engineers
- 1.1.6 Hole Openers & Under-reamers, 4.1.5 Processing Equipment, 1.11.4 Solids Control, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.10 Drilling Equipment, 1.5.1 Surveying and survey programs, 4.1.2 Separation and Treating, 1.6.1 Drilling Operation Management, 1.14 Casing and Cementing, 4.2.3 Materials and Corrosion, 4.1.6 Compressors, Engines and Turbines, 3 Production and Well Operations, 4.3.4 Scale, 4.2 Pipelines, Flowlines and Risers, 5.6.4 Drillstem/Well Testing, 1.11 Drilling Fluids and Materials, 1.5 Drill Bits, 1.6 Drilling Operations, 1.14.1 Casing Design, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.9 Tanks and storage systems, 2.2.2 Perforating
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Between Oct. 1983 and Aug. 1985, Monsanto Oil Co. drilled a 24,877-ft [7583-m] -deep well on the Madden anticline in Wyoming's Wind River basin to evaluate the unexplored potential below the 17,000-ft [5182 m] -deep Cretaceous Cody formation. Three casing strings from surface and four liners were run, including a record depth and weight 16-in. [40.6-cm] string. The well tested at 20 MMcf/D [566 x 103 M3 /d] with minimal drawdown from the Mississippian Age Madison formation at 23,800 ft [7254-m).
Gas production in the Madden area is from a huge anticlinal structure located in the Wind River basin in Fremont and Natrona Counties, WY (Fig. 1). The Madden Deep Unit was formed before the 1986 discovery of relatively shallow gas in the Tertiary Age Lower Fort Union formation. Development drilling from 1968 through 1973 concentrated on the Lower Fort Union formation. Well depths averaged 10,000 ft [3050 m]. In 1973 a program to explore deeper formations was initiated. Targets included the Upper Cretaceous Lance, Mesaverde, and Cody formations. These wells ranged in depth from 14,000 ft [4270 m] to a deep-flank Cody formation test at 22.700 ft [6920 m].
There are currently 60 productive gas wells on the Madden structure (Fig. 2). These wells cover a surface area 16 x 6 miles [26 x 10 km]. Producing sands on the crest are located at depths of 5,600 to 17.000 ft [1700 to 5200 m]. The deepest off-crest production is from less than 19,000 ft [5800 m].
In Oct. 1983, the Bighorn drilling began to evaluate more than 7,000 ft [2 1 00 m] of gross unpenetrated interval between the Cody formation and the Precambrian. The Bighorn reached the Precambrian interval and a total depth (TD) of 24,877 ft [7583 m] & Aug. 1985. 640 days after spudding. Total well cost was S25 million. A successful production test in the Mississippian Age Madison formation established the production depth record for the Rocky Mountain area.
Because of inherent difficulties encountered while drilling in the Wind River basin, few wells have penetrated to the Madison formation. The Madison penetration closest to the Bighorn is 30 miles [48 km] southeast of the Madden Deep Unit. High pressures, shallow gas and water zones, extensive sloughing-shale sections. high temperatures, and multiple lost-circulation zones all require extreme care in planning and drilling a Wind River basin deep test.
As depicted by the plot of mud weight vs. depth in Fig. 3, most of the structure is overpressured. Normal pressure gradients exist only over the very top and bottom of the structure. Formations with significant degrees of relative overpressurization are the Lower Fort Union at 5,600 ft [1700 m], the Mesaverde at 14,500 ft [4400 mi, and the Frontier at 20,000 ft [6100 m]. The design problem is further complicated by 3,000 psi [20.7 MPa] of pressure depletion resulting from production from the Shannon sands of the Cody formation located at approximately 17,000 ft [5200 m] on the crest of the structure.
The casing program for Bighorn is shown in Fig. 3. Three surface strings (30, 20, and 16 in. [76.2, 50.8. and 40.6 cm]) were required to reach 14,000 ft [4270 m]. From 14,000 ft [4270 m] to TD at 24,877 ft [7583 m], four liners (11 7/8, 9 3/8", 7 3/4, and 5 1/2 in. [30.2, 25.1, 19.7, and 14 cm]) were required.
The casing design was complicated by high and variable formation pressures, hole-size tolerances, and the anticipation of sour gas in the deep exploratory section of the well. String design used both API load capacity design and triaxial stress analyses. An array of possible drilling and production conditions was used in the casing design models. Specific casing depth requirements are described in Table 1.
Quarles Drilling Corp's Rig 25 was used to drill Bighorn 1-5. Rig 25 is a 30,000-ft [9144-m] silicon control resistor rig with a mast rating of 2,000,000 lbm [907 200 kg] with 1,000,000 Ibm [454 000 kg] setback capacity. Rig power was supplied by a 6,500-hp [4850-kW] gas turbine backed up by four diesel engines. Field gas was used for fuel. The traveling blocks and hook were rated at 1,000 tons [907 200 kg] with a 650-ton [590 000-kg] swivel. The drawworks were 3,000 hp [2240 kW] grooved for 1 5/8-in. [4.1 -cm] drilling line.
the mud circulation system comprised two 1,600-hp (1190-kW) and one 1,000hp 746kw triplex mud pumps, mud tanks with 1.650-bbl [262 -M3] capacity, a dual tandem double-screen shale shaker, an 8-cone desander, and a 16-cone desilter.
0 to 1,490 ft [0 to 454 and the 36-in. [91 4-cm] hole was opened in three states. A 17 1/2-in. (44.40cm) pilot hole was drilled with a nonrotating stabilizer 40 ft [12 m] above the bit. The hole was then opened with a slick bottomhole assembly (BHA) to 26 in. [66 cm] and subsequently to 36 in. [91.4 cm]. As a result of slick assemblies, some lateral bit movement occurred, creating ledges in the hole. On the first attempt, the 30-in. [76.2-cm] casing was unable to pass the ledges. The ledges were successfully removed with a packed hole assembly comprising a 26-in. [66-cm] pilot bit, two 36-in. [91 1-cm] hole openers separated with a 10-ft [3-m] drill collar, a shock sub, and a nonrotating sub. A packed hole assembly will be considered from the outset in all future wells.
The 30-in. [76.2-cm] casing was cemented without problems by the inner string method. The inner string method uses the drillstring to carry the cement down the casing. The 30-in. [76.2-cm] connector was a quick, makeup stab type. A 30-in. [76.2-cm], 1,000-psi [6.9-MPa] diverter system was nippled up and the hole was displaced with invert mud.
1,490 to 7,024 ft [454 to 2141 m]. A 17 1/2 -in. [44.4-cm] pilot hole with a packed BHA was initially drilled to 5,550 ft [ 1692 m]. The hole was logged to obtain shallow-reservoir information. This segment was then opened to 26 in. [66 cm] by use of a packed BHA. The remainder of this section was drilled with a 26-in. [66-cm] bit without a preceding pilot hole.
The 20-in. [50.8-cm] drillstring was cemented with the inner string method. Gas from the Lower Fort Union formation percolated through the cement to the surface. The 20-in. [50.8-cm] casing was perforated and the 20 x 30-in. [50.8 x 76.2-cm] annulus was cement squeezed. Future wells will attempt to prevent gas channeling through a reformulation of the cement.
The mud used during this section had an oil/water ratio of 72/25 and high-temperature/high-pressure water loss of 10 to 15 cm3. The mud was not relaxed beyond this because of potential shale problems.
At this point, the wellhead and landing base were welded on the 20-in. [50.8-cm] casing. All welds were heat treated. An 18 3/4 -in. [47.6-cm], 10,000-psi [69-MPa] blowout preventer and choke manifold were nippled up.
7,024 to 13,970 ft [2141 to 4258 m]. The drift diameter of the 20-in. [50.8-cm] casing requited the use of nonsandard size API 5-3-5 type 18 1/4in. 46.4-cm] bits.
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