Physical Observations and Mapping of Cracks Resulting from Hydraulic Fracturing In Situ Stress Measurements

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.Abstract. For many years hydraulic fracturing has been used as a stimulation tool for oil and gas reservoirs. Hydraulic fracturing has also been developed as a method to measure in situ stresses. The correspondence between the measured fluid pressures and the in situ stresses has been studied and is fairly well understood. The characteristics of the fractures created by hydraulic fracturing are not understood. Information about the fractures at the wellbore can be obtained by a number of techniques but knowledge of the fractures behavior away from the well is very limited. The fracture behavior may determine either the stress direction for a stress measurement or the difference between a good or bad stimulation job.To better understand the hydraulic fracture technique, experiments were performed in a tuff formation in Rainier Mesa performed in a tuff formation in Rainier Mesa at the Nevada Test Site. The purpose of the experiments was to determine the stresses in the mesa; and, to examine the fracture behavior produced by the hydraulic fracture technique. Hydraulic fracturing was performed in both vertical and horizontal performed in both vertical and horizontal boreholes with a maximum overburden of 1490 ft. All experiments were done in the vicinity of an existing tunnel complex but sufficiently remote to avoid unwanted boundary effects. The stresses were determined from the hydraulic fracture data using the theory of Fairhurst and Haimson. The maximum horizontal, vertical and minimum horizontal principal stresses for 1365 ft. of overburden principal stresses for 1365 ft. of overburden were 1788 psi, 1183 psi, and 1015 Psi, respectively. A number of the fractures produced during the tests were mapped by produced during the tests were mapped by mining from the tunnel complex and physically examining the fractured formation. physically examining the fractured formation. Dyed water was used for all the holes drilled in the tunnel complex. Dyed cement grouts were used to tag the fractures formed in a 1365 ft. deep hole from the top of the mesa. Two fracture jobs were performed at two locations in the vertical hole using yellow and red grouts. These fractures were essentially vertical and parallel.