Friday, February 20, 2009

Natural gas storage in Picacho basin salt deposits

Companies have been looking at the Picacho basin between Tucson and Phoenix for a number of years as an attractive place to develop giant caverns in underground salt deposits to storage natural gas for use in Arizona during peak demand periods. Today's Arizona Daily Star carried a front page headline describing a proposal by Houston-based Multifuels LP for $220 million project. [right, illustration of natural gas storage in salt caverns. Credit, DOE-EIA]

In 2005, Unocal and El Paso Natural Gas drilled three stratigraphic holes in the Picacho basin to investigate the feasibility of storing natural gas in deep subsurface salt. Unocal drilled the 1-27 Mesa in Sec 27-T7S-R8E to a total depth of 4,895 ft in February. El Paso drilled the 1-20 State in Sec 20-T7S-R8E to a total depth of 3,316 ft in August and the 1-11 State in Sec 11-T7S-R8E to a total depth of 3,170 ft in September. All three stratigraphic wells were plugged. The three wells indicated a sufficient volume of subsurface salt for storing natural gas.

In October 2006, El Paso drilled a third stratigraphic hole, the 1-21 AGS in Sec 21-T7S-R8E, to a total depth of 8,784 ft to collect information about subsurface units below the salt. The 1-21 AGS is temporarily abandoned pending additional analysis.

Three drill-stem tests in the Humble (now Exxon) hole in Sec 2-T8S-R8E indicated chlorides ranging in concentration from 89,000-113,000 ppm in conglomerates at depths of 8640-8840 ft. Humble reported evaporites, mostly anhydrite, at depths from 1700 to 8500 ft. This hole is about four miles east of Eloy. That concentration is 2-3 times the salinity of seawater.

There are bills in the Arizona Legislature this session that would exempt brine disposal wells for natural gas storage projects in salt from the ADEQ aquifer protection program. Current law requires all groundwater, regardless of quality or salinity, to be treated as drinking water sources. The brine wells would still have to meet EPA requirements and Clean Drinking Water standards.

[AZGS Oil & Gas Administrator Steve Rauzi contributed to this post.]

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