Los Alamos National Laboratory has conducted a number of pumping and flow-through tests at the H o t Dry Rock (HDR) test site at Fenton Hill, New Mexico. These tests consisted of injecting fresh water at controlled rates up to 12 BPM (32 p/s) and surface pressures up to 7,000 p s i (48 MPa) into the HDR formation at depths from 10,000 - 13,180 feet (3050 -4000 m ). The formation is a naturally fractured granite at temperatures of about 250OC. The matrix porosity is <1% and permqability is on the order of 1 nD (lo4 m Z ). Hence most of the injected fluid is believed to move through fractures. There has been no evidence of fracture breakdown phenomena, and hence it is believed that pre-existing joints in the formation are opened by fluid injection. Water losses during pumping are significant, most likely resulting from flow into secondary fractures intersecting the main fluid conducting paths. The pressure-time response observed in these tests can be interpreted in terms of non-isothermal, fracture-dominated flow. A s the fluid pressure increases from small values to those comparable to fracturing pressures, the formation response changes from linear fracture flow to the highly nonlinear situation where fractur e lift off occurs. A numerical heat and mass flow model was used to match the observed pressure response. Good matches were obtained for pressure build up and shut-in data by assigning press u r e dependent frac t u r e and leak-off permeabilities.

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