Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern Germany

Geothermal Energy

Science – Society – Technology

Table 5 Effective stress sensitivity coefficients of the tested rock samples at an effective pressure of 28 MPa

Sample	Lithology	\({S}_{s}^{\varPhi }\)	\({S}_{s}^{k}\)	\(c\)(\({C}_{\varPhi }\))	\(b\)	\(\beta \)
Sample	Lithology	10^–2 MPa⁻¹	MPa⁻¹	10^–4 MPa⁻¹	10^–2 MPa⁻¹	–
L1	Limestone	0.43	0.16	7.13	2.12	28.3
L2	Limestone	0.66	0.23	9.71	3.67	34.0
L3	Limestone	0.51	0.18	5.03	2.74	46.3
L4	Limestone	0.42	0.13	3.69	1.29	34.2
L5	Limestone	0.34	–	4.60	–	–
dL1	Dol. limestone	0.41	0.11	4.49	1.01	22.6
dL2	Dol. limestone	0.36	0.29	4.31	3.24	74.7
D1	Dolostone	0.30	0.13	2.86	1.13	36.1
D2	Dolostone	0.35	0.07	1.82	1.25	56.7
D3	Dolostone	0.22	0.06	2.88	1.00	32.8
D4	Dolostone	–	0.06	–	0.87	–
D5	Dolostone	0.32	0.24	3.41	2.25	63.0
D6	Dolostone	–	0.11	–	1.51	–

\({S}_{s}^{\varPhi }\) stress sensitivity coefficient for porosity, \({S}_{s}^{k}\) stress sensitivity coefficient for permeability, \(c\) porosity stress coefficient (equals pore compressibility \({C}_{\varPhi }\)), \(b\) permeability stress coefficient, \(\beta \) porosity sensitivity exponent