Injection and Monitoring of Simulated Solid Waste - A Field Demonstration

Robert J. Withers, Richard G. Keck

In 1993, ARCO injected simulated waste in a technology demonstration of monitored fracture injection for environmental disposal. Over a five day period, 3 million pounds of sand in a bentonite slurry were injected with 50,000 barrels of water into the Upper Frio formation at 4500 feet depth at a site near Jasper, Texas. The site was selected after reviewing candidate sites from around the United States.

Protection of surrounding ground water is required for injection of solid waste. Extensive testing of the stress contrast between the injection interval and the surrounding shale allowed confident modeling of the fracture containment. The fracture orientation was predicted from regional stress investigations, microfracture studies and tiltmeter studies. These results provided a wide range of uncertainty due to the friable nature of the injection interval.

The fracture location was determined in the field with a real-time seismic monitoring system. A total of 150 geophones was deployed in two dedicated monitor wells placed along the projected fracture direction. Over 2000 microseismic events were recorded and a subset located using a constant velocity inversion model calibrated by downhole shots.

As predicted, the fracture did not grow into the bounding shale formation. In the first injection cycle, the fracture grew to the formation height of 150 feet and to a length of 700 feet. The length increased to 1200 feet during the second injection cycle. In the third injection cycle of about 1 MMbls, the fracture grew only to 900 feet long and appeared to branch from the original fracture orientation.

Results from the stress contrast studies, orientation and length predictions, and the location of the fracture as it grew during the experiment will be presented.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995