Seismic Attribute Processing to Find Deep Aquifers

The scarcity of water in arid and semi-arid regions has increased interest in sources of water much deeper than traditionally considered economic. Many projects have targeted fresh to brackish water sources at depths of 2,000 to over 5,000 feet. In many formations the potential yield of a well varies based on stratigraphic changes making it difficult to predict the potential yield of a given location without more information. The cost of drilling to such depths limits the availability of data and makes developing these resources risky and expensive.

Seismic reflection surveys collect data on the propagation of seismic waves to depths of several thousand feet. Developed by the oil and gas industry, seismic data can be used to map structural features in fine detail. Modern processing and interpretation techniques can map aquifer units, faults, and other structural features that can control well yield. With a little more processing, the shape of the waveforms can identify changes in the stratigraphy, porosity, and pore fluid characteristics in a unit. Seismic attribute processing can be used to identify permeable features such as narrow channel sand deposits at depths of thousands of feet to target permeable zones.

The cost to acquire reflection data is relatively high, which has limited the application of the method for water supply applications. Fortunately many areas have libraries of existing reflection data from previous oil and gas exploration activities. This data can often be purchased for a few thousand dollars per mile and used to map units that can potentially serve as aquifers.

Several case histories will be presented to demonstrate how modern interpretation methods can be used on 2D or 3D seismic reflection data to map features such as sand channels, faults, and shale pinch outs in aquifer units and direct drilling programs toward higher yielding sites.