Geophysical investigations at Flowers Ranch, Hemphill County, Texas

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2011

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Intera Inc. requested technical assistance from the Bureau of Economic Geology (BEG) to conduct ground-based geophysical surveys at Flowers Ranch to acquire noninvasive data that would help determine whether there was evidence for contamination of sedimentary strata and groundwater between the base of the Ogallala Formation and the ground surface near the Jones 5-49H well on the Flowers Ranch in Hemphill County, Texas. On May 19-21, 2011, BEG researchers conducted frequency- and time-domain electromagnetic induction (EM) geophysical measurements near the well to identify ground conductivity anomalies that could be associated with the presence of saline water introduced into the shallow subsurface during drilling activities at the site.

EM surveys consisted of:

  1. Three ground-conductivity transects (Lines 1, 2, and 3, Fig. 1) in the vicinity of the well, the blowout feature on the bank of the creek east of the well, and along the axis of the creek upstream to measure apparent electrical conductivity of the ground to depths from a few to a few tens of meters.
  2. Five time-domain EM soundings on the periphery of the 5-49H well pad (FR2, FR3, FR4, FR5, and FR7, Fig. 1) intended to produce multi-layer conductivity profiles between the ground surface and the base of the Ogallala Formation that could reveal conductivity anomalies that might be indicative of volumetrically significant salinization within the upper 300 m of the subsurface.

Dry soil and ground that is partly or completely saturated with fresh water have relatively low electrical conductivity (generally a few to a few tens of milliSiemens per meter [mS/m]; McNeill, 1980a). Ground that has been salinized through the introduction of highly conductive saline fluids (Hem, 1985) commonly associated with oil and gas drilling and production activities has much higher conductivities ranging from a few tens to a few hundred mS/m. Electrical geophysical methods such as EM and resistivity are thus highly effective in identifying salinized soil and groundwater.

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