ABSTRACT:

Geothermal energy production by water circulation in natural and/or man-made fracture systems is referred to as enhanced or engineered geothermal systems (EGS). Good understanding of the induced fracture properties is essential for estimating /evaluating the performance of the system. In this work, we study the hydraulically induced fracture properties on a laboratory scale using cold water circulation and tracer analysis. To achieve this goal, we first have performed reservoir stimulation using 13 inch ×13 inch ×13 inch cubical rock samples. And then the rock block was heated to a uniform temperature of about 78°C. Cold water was injected into the central well and collected from nearby multi production wells. The distance between the injection well and production wells are 3.5 inch. Temperatures in the wells and on the rock surfaces were recorded. The maximum temperature drop was as high as 57.1°C in the injection well and about 29°C in one production well producing most of the fluid during the circulation phase. The injection pressure history indicates that the cold-water injection dramatically increases the permeability of the fracture due to the cooling effect. Calculation shows that 17.3 % of the total stored heat in the tested block was extracted during this circulation phase. Based on the tracer test result and reconstructed 3D fracture geometry, the fracture volume is estimated to be 8.6 ml with a width of about 174µm.

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