Physical property relationships of the Rotokawa Andesite, a significant geothermal reservoir rock in the Taupo Volcanic Zone, New Zealand

Geothermal Energy

Science – Society – Technology

Table 2 Results of quantitative microstructural characterization

Sample name	Crack density for intercepts parallel to orientation axisP\|\| (mm⁻¹)	Crack density for intercepts perpendicular to orientation axisP \|(mm⁻¹)	Crack area per unit volume Sv (mm²/mm³)	Anisotropy factorΩ_2,3	Connected porosity (vol%)
27_21_0B	13.73	13.53	13.06	0.01	14.91
28_10_5A	4.10	4.41	8.33	0.06	7.47
27_20_4_B	1.83	2.06	3.77	0.08	4.37
27_3_3B	4.77	4.77	9.55	0.01	9.81
30_22_4A	2.77	2.62	5.48	0.01	6.49
28_10_9B	3.84	3.90	7.71	0.03	7.42
28_12_1	4.83	4.65	9.59	0.02	7.89
30_21_1B	2.93	2.91	5.85	0.01	7.47
27_21_3A	5.80	5.13	11.31	0.09	16.3
28_10_6C	2.97	2.87	6.38	0.05	5.97

As discussed in the section on microstructural characterization, crack densities were calculated on thin section samples to ascertain crack areas per unit volume using the optical microscope method (Underwood [1970]).