New Mexico Geological Society Annual Spring Meeting — Abstracts

Two exploratory wells were drilled in the Rio Puerco Valley west of Rio Rancho during the summer of 2007 by Sandoval County and a residential developer. Exp-6 spudded in thin alluvial cover just east of the surface trace of the Moquino fault and ended 3,850 feet below ground surface (bgs). It was screened between 3,598 and 3,809 ft bgs in the Aqua Zarca member of the Chinle Formation and in the San Andres and Glorieta Formations, respectively. Exp-5 (total depth of 6,450 ft bgs, reaching Pre-Cambrian basement rock at 6,350 ft) was screened in six intervals between 3,360 and 4,820 ft bgs from the Aqua Zarca to the Yeso Formation. Exp-6 yielded approximately 600 gallons per minute (gpm) of water. Exp-5 initially produced approximately 20 gpm of artesian flow. After a commercial fracturing procedure, Exp-5 flowed at a sustained rate of approximately 150 gpm. Groundwater from the wells contains approximately 12,000 mg/l TDS, 3,100 mg/l chloride, and 4,400 mg/l sulfate.

Drilling Exp-6 through the Moquino fault made for difficult stratigraphic correlation until reaching the Todilto gypsum beds at approximately 1,685 ft bgs. After drilling Exp-5, units correlated between the two holes up to 1,415 ft bgs in Exp-6. Using that depth for the intersection of the fault with the well and an estimated surface trace of the fault 230 ft west of the well indicates the fault dips approximately 81 degrees east.

The Moquino fault juxtaposes the marine shales of the Mancos Shale (Kmz) and the deltaic, coal bearing sandstones of the Menefee Fm. Vertical displacement may be as much as 2,285 to 2,785 ft based on published unit thicknesses. The displacement on the Moquino fault is an example of how geologic structure can impact the economics of resource development. On the west side of the fault, the top of the producing interval is 3,598 ft bgs. On the east side of the fault, the top of the producing zone could be as deep as 6,383 ft bgs, nearly doubling the cost to drill for that zone.