Wildcatters test the deep Anadarko basin: Pioneering spirit leads to record-depth wells
At the start of the 1970s, the U.S. petroleum industry was stuck between a rock and a hard place. The government had stripped producers of several key tax incentives, was limiting drilling on federal lands, and withholding approval of a crude oil pipeline across Alaska. Adding to the hardship, most of the supergiant U.S. oil fields had long been discovered, and production in these mature provinces was in steep decline.
However, the country did have abundant supplies of natural gas, but low prices and the expense of building miles of pipelines for transportation were limiting factors. To make drilling for natural gas profitable, the geological prospect would have to have vast potential to produce large amounts of gas at high flowrates, with minimal production costs. With offshore drilling still in its infancy, the Anadarko basin in western Oklahoma was one of the last remaining prospects in the Lower 48 that satisfied all of these requirements.
During the early 1970s, relatively deep exploratory efforts in the shelf area of the basin had established commercial production in Pennsylvanian, Mississippian and Ordovician sediments, at depths down to 20,600 ft. The information gained from these deep wells was used to further define the basin’s stratigraphy and geological structures, using refined seismic techniques. The geophysical analysis supported the hypothesis that formation thickness increased south of the established fields, and that another 10,000 ft of potentially productive sediments lay beneath the 20,600-ft benchmark.
Wildcatters roll the dice. In the true spirit that defined the U.S. oil industry at the beginning of the century, Lone Star Producing Co. and partner Glover Hefner Kennedy (later GHK) accepted the immense challenge and set out to test the deepest portion of the Anadarko basin southwest of Elk City, Okla. The companies had identified two Pennsylvanian structures on jointly owned acreage, and proposed to test each separate geologic feature with a 30,000-ft well. To reach this extreme depth required extensive planning and successful execution of a multitude of engineering firsts. Additional challenges included high temperatures, and constructing a large and extremely heavy casing string that would enable commercial production from a record depth.
On Aug. 4, 1970, drilling commenced on the 1 E.R. Baden Unit, in Beckham County, Okla., using Loffland Brothers Rig 32, the largest, most powerful land-based unit operating at the time, Fig. 1. The well reached a TD of 30,050 ft on Feb. 29, 1972, in the Ordovician-age Viola limestone. An open-hole test of the Hunton limestone from 28,448 ft to 29,768 ft, which was treated with 15,000 gal of acid, produced no gas or water, and the formation was abandoned as tight. The well was subsequently plugged back to 20,012 ft and completed in the Atoka as a small gas producer from perforations between 16,190 ft and 17,382 ft. With a total well cost of approximately $5.5 million, the well was an economic dry hole.
However, the industry did establish that it could drill and successfully set casing on extremely deep operations. Two of the most notable engineering achievements on the Baden well, besides the record depth, were setting a 133/8-in. casing string, with a total weight of 1.21 MMlb, at 15,416 ft, and hanging 95/8-in. liner with tie-back at 23,392 ft.
Bertha Rogers 1. On Nov. 25, 1972, Lone Star Producing spudded Bertha Rogers 1 in Washita County, Okla. The well reached a TD of 31,441 ft on April 13, 1974, after 504 days, a world record depth that stood for several years. During drilling operations, the well encountered enormous downhole pressure, up to 25,000 psi, and high temperature reaching 475°F, but drilling stopped when the BHA hit molten sulfur that melted the drill bit. The well was plugged back and completed in the Granite Wash from 13,000 ft to 13,110 ft, flowing 6 MMcfgd after acid treatment. Although the well was classified as a new field discovery, with a total well cost of approximately $7 million, it was considered an ultra-deep dry hole. Combined with low commodity price and exorbitant deep drilling and completion costs, the Bertha Rogers 1 essentially ended the quest for hydrocarbons in the basin down to 30,000 ft.
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