Use of 3D Seismic to Land Horizontal Wellbores in Thin Beds: Potash Solution Mining Near Moab Utah

Robert J. Grundy¹ and Hugh Harvey^2
1Consultant, Morrison, CO
²Intrepid Mining LLC, Denver, CO

Intrepid Mining LLC acquired the “Potash” 3d survey in 2001 over its Cane Creek Potash Mine near Moab Utah. The 3d had duel objectives: 1) mapping of the Cane Creek Anticline to aid in solution mining of potash; and 2) mapping of the Cane Creek anticline for oil and gas potential.

Using the seismic character of the overlying clastic layer as a guide, Intrepid Mining LLC in 2002 drilled the first horizontal well solely for solution mining of potash (KCL)in the Intrepid 27H wellbore. This wellbore targeted “potash 9”, a sylvinite (sylvite and halite) layer within evaporate cycle 9 of the Paradox Formation (this potash layer had not been previously mined in the Cane Creek Potash Mine).This wellbore was followed by a “fork” pattern of the 28H well that comprised 15,000 feet of lateral. In 2005 a second fork pattern was drilled with the 29H wellbore. These wellbores targeted the northeast flank of the Cane Creek Anticline which is not as structurally complex as the crest of the structure. The 27H and 28H well used a gamma ray tool (potassium has a highly radioactive signature) to stay in zone. Since the sylvinite layer is encased in halite, it was hard to tell whether the bore was drifting upwards or downwards out of zone. This was remedied in 29H well with an azimuthal gamma ray tool. Other problems encountered were: a slight sag in the seismic under the shallower mine cavern and the discontinuous nature of the potash zone. The seismic was accurate to plus or minus 20 feet.

The secondary objective of the Potash 3d survey was the evaluation of the oil and gas potential of the Cane Creek Anticline in and around the potash mine. In 1956 MODCO drilled a well adjacent to the future Cane Creek Potash Mine that produced oil from the Cane Creek member of the Paradox Formation. In addition, Texas Gas Sulfur encountered gas shows in the Cane Creek while drilling a delineation well for the future potash mine. Synthetic seismic modeling of the Cane Creek member shows amplitudes drops in the Cane Creek reflector where it develops porosity. Cane Creek amplitude loss was detected from the 3D survey under the potash mine . Exploratory drilling of the Cane Creek is pending.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado