NATURAL GAS EXPLOSIONS IN HUTCHINSON, KANSAS: GEOLOGIC FACTORS

On the morning of January 17, 2001, a gas explosion occurred in downtown Hutchinson. Later that day, gas geysers began erupting two miles to the east along the edge of Hutchinson. These events coincided with a major gas leak in the S-1 storage well at the Yaggy gas storage area located 7 miles northwest of Hutchinson. The facility is a major gas storage facility where gas is stored in salt caverns within the Lower Permian Hutchinson Salt Bed.

Fifty-four vent and observation wells were drilled in the Yaggy and Hutchinson area. Seismic profiles, gas shows while drilling, wireline logs, and two cores delineate a shallow (420 to 240 ft deep), narrow (100’s of ft) conduit, closely corresponding to the crest of a narrow, low-relief, asymmetric northwesterly plunging anticline. With exception of vent well DDV #64, gas is limited to an approximately 15-ft thick interval consisting of three thin (2-3 ft thick) beds of low porosity micritic dolomite (called the 3-finger dolomite) and gypsiferous shales. The beds lie at the contact between the Lower Permian Ninnescah and Wellington shales and are probably equivalent to the Milan Limestone Member.

Natural gas at high pressure apparently migrated from a casing leak at a depth of 595 ft (just below the top of salt and 184 ft above the top of the salt cavern) to the shallow dolomitic horizon (420 ft), then updip along the crest of the anticline. Gypsum beds above the dolomite may have acted as seals to prevent further vertical movement of the natural gas. Pressure-induced parting along a pre-existing fracture system residing on the anticlinal crest is suggested by: 1) small, discontinuous fractures in the dolomite, 2) east-west oriented partial fractures in an FMS log from observation well OB #2, 3) gas pressure history, and 4) volumetric and flow calculations.