Introduction
1. Geological setting
Fig. 1. Location of the study area and sedimentary facies of shale at the bottom of Silurian Longmaxi Formation. |
2. Samples and experiments
2.1. Porosity and permeability experiment at high temperature and high pressure
2.1.1. Sample information
Table 1. Basic parameters of shale samples in porosity and permeability experiment |
Sample No. | Depth/m | TOC/% | Ro/% | Mineral content/% | Length/ mm | Diameter/ cm | Density/ (g·cm-3) | ||||
---|---|---|---|---|---|---|---|---|---|---|---|
Quartz | Clay | Calcite | Dolomite | Others | |||||||
A1-1 | 3847.26 | 4.41 | 2.21 | 30 | 31 | 25 | 19 | 4 | 4.952 | 2.516 | 2.437 |
A1-2 | 3847.50 | 4.41 | 2.93 | 27 | 29 | 24 | 17 | 3 | 2.932 | 2.516 | 2.554 |
A1-3 | 3847.73 | 4.41 | 2.21 | 24 | 30 | 23 | 18 | 5 | 4.798 | 2.514 | 2.514 |
A1-4 | 3847.87 | 4.41 | 2.93 | 26 | 29 | 22 | 19 | 4 | 4.818 | 2.514 | 2.531 |
A1-5 | 3848.20 | 5.35 | 2.21 | 56 | 22 | 10 | 7 | 5 | 6.162 | 2.518 | 2.480 |
B1-1 | 3857.33 | 2.83 | 3.37 | 43 | 41 | 1 | 5 | 10 | 4.386 | 2.520 | 2.559 |
B1-2 | 3861.44 | 4.23 | 3.37 | 56 | 27 | 1 | 8 | 6 | 3.640 | 2.520 | 2.515 |
B1-3 | 3864.72 | 7.83 | 2.99 | 58 | 23 | 4 | 9 | 10 | 3.324 | 2.518 | 2.499 |
B1-4 | 3864.87 | 7.83 | 2.99 | 53 | 24 | 5 | 10 | 8 | 4.492 | 2.520 | 2.497 |
B1-5 | 3865.64 | 5.08 | 2.99 | 44 | 17 | 12 | 18 | 9 | 3.452 | 2.522 | 2.530 |
2.1.2. Experimental equipment, experimental objective and scheme
2.2. Rock mechanics experiment at high temperature and high pressure
2.2.1. Samples
Table 2. Basic parameters of shale samples in rock mechanics experiment |
Sample No. | Depth/m | Mineral content/% | Lithology | Experimental conditions | ||||
---|---|---|---|---|---|---|---|---|
Quartz | Clay | Calcite | Dolomite | Confining pressure/MPa | Temperature/ °C | |||
A2-1 | 3706.84 | 45 | 27 | 9 | 12 | Carbonate-bearing siliceous shale | 30 | 80 |
A2-2 | 50 | 100 | ||||||
A2-3 | 70 | 120 | ||||||
B1-1 | 3859.18 | 57 | 29 | 1 | 6 | Siliceous shale | 30 | 80 |
B1-2 | 50 | 100 | ||||||
B1-3 | 70 | 120 | ||||||
B2-1 | 4092.17 | 58 | 22 | 5 | 9 | Siliceous shale | 10 | 60 |
B2-2 | 30 | 80 | ||||||
B2-3 | 50 | 100 | ||||||
B2-4 | 70 | 120 |
2.2.2. Experimental equipment, objective and scheme
3. Results
3.1. Porosity and permeability experiment at high temperature and high pressure
Table 3. Results of porosity and permeability experiment at high temperature and high pressure for shale samples from Well A1 |
Confining pressure/ MPa | Temperature/°C | A1-1 | A1-2 | A1-3 | A1-4 | A1-5 | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | ||||||
10 | 60 | 7.06 | 3.12 | 8.08 | 0.94 | 4.05 | 1.28 | 3.57 | 0.69 | 4.87 | 3.69 | ||||
20 | 70 | 5.94 | 1.91 | 6.52 | 0.54 | 3.08 | 0.75 | 3.05 | 0.41 | 3.91 | 2.68 | ||||
30 | 80 | 5.53 | 1.15 | 5.74 | 0.33 | 2.65 | 0.46 | 2.71 | 0.19 | 3.60 | 1.55 | ||||
40 | 90 | 5.15 | 0.86 | 5.45 | 0.15 | 2.52 | 0.25 | 2.57 | 0.11 | 3.24 | 1.04 | ||||
50 | 100 | 4.96 | 0.68 | 5.06 | 0.08 | 2.36 | 0.14 | 2.34 | 0.08 | 3.09 | 0.58 | ||||
60 | 110 | 4.75 | 0.59 | 4.78 | 0.06 | 2.25 | 0.10 | 2.24 | 0.07 | 2.87 | 0.47 | ||||
70 | 120 | 4.66 | 0.41 | 4.59 | 0.05 | 2.16 | 0.07 | 2.15 | 0.05 | 2.76 | 0.27 | ||||
60 | 110 | 4.69 | 0.42 | 4.64 | 0.05 | 2.19 | 0.08 | 2.20 | 0.05 | 2.80 | 0.28 | ||||
50 | 100 | 4.77 | 0.47 | 4.72 | 0.06 | 2.24 | 0.08 | 2.28 | 0.05 | 2.89 | 0.30 | ||||
40 | 90 | 4.85 | 0.49 | 4.87 | 0.08 | 2.31 | 0.10 | 2.42 | 0.05 | 3.00 | 0.43 | ||||
30 | 80 | 4.96 | 0.60 | 5.01 | 0.10 | 2.42 | 0.11 | 2.48 | 0.07 | 3.20 | 0.59 | ||||
20 | 70 | 5.19 | 0.80 | 5.36 | 0.14 | 2.49 | 0.16 | 2.57 | 0.08 | 3.39 | 0.84 | ||||
10 | 60 | 5.54 | 1.14 | 5.93 | 0.22 | 2.80 | 0.28 | 2.79 | 0.11 | 3.72 | 1.47 |
Table 4. Results of porosity and permeability experiment at high temperature and high pressure for shale samples from Well B1 |
Confining pressure/ MPa | Temperature/°C | B1-1 | B1-2 | B1-3 | B1-4 | B1-5 | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | Porosity/% | Permeability/ 10−6 μm2 | ||||||
10 | 60 | 3.31 | 9.10 | 3.25 | 3.43 | 4.06 | 6.26 | 4.72 | 0.11 | 4.10 | 5.09 | ||||
20 | 70 | 2.38 | 5.69 | 2.61 | 2.51 | 3.04 | 2.71 | 3.86 | 0.08 | 2.63 | 2.23 | ||||
30 | 80 | 1.87 | 3.05 | 1.97 | 1.69 | 2.59 | 1.62 | 2.96 | 0.06 | 1.83 | 1.02 | ||||
40 | 90 | 1.64 | 2.00 | 1.73 | 1.22 | 2.28 | 1.27 | 2.54 | 0.04 | 1.65 | 0.52 | ||||
50 | 100 | 1.53 | 1.07 | 1.63 | 0.79 | 2.05 | 1.04 | 2.40 | 0.03 | 1.41 | 0.38 | ||||
60 | 110 | 1.37 | 0.79 | 1.54 | 0.65 | 2.00 | 0.77 | 2.24 | 0.02 | 1.31 | 0.23 | ||||
70 | 120 | 1.29 | 0.48 | 1.49 | 0.49 | 1.86 | 0.60 | 2.13 | 0.02 | 1.19 | 0.13 | ||||
60 | 110 | 1.30 | 0.49 | 1.51 | 0.52 | 1.88 | 0.62 | 2.17 | 0.02 | 1.23 | 0.14 | ||||
50 | 100 | 1.37 | 0.54 | 1.53 | 0.53 | 1.91 | 0.73 | 2.20 | 0.02 | 1.32 | 0.15 | ||||
40 | 90 | 1.46 | 0.69 | 1.58 | 0.54 | 1.99 | 0.76 | 2.27 | 0.02 | 1.40 | 0.16 | ||||
30 | 80 | 1.52 | 0.89 | 1.73 | 0.63 | 2.07 | 0.81 | 2.37 | 0.02 | 1.46 | 0.21 | ||||
20 | 70 | 1.73 | 1.14 | 1.96 | 0.71 | 2.34 | 1.11 | 2.57 | 0.03 | 1.61 | 0.34 | ||||
10 | 60 | 1.99 | 1.75 | 2.42 | 1.05 | 2.79 | 2.25 | 2.97 | 0.04 | 1.97 | 0.84 |
Fig. 2. Variation of porosity and permeability with temperature and pressure for deep shale samples from Well A1 (dotted lines indicate the recovery curves of porosity and permeability when temperature and pressure decrease). |
Fig. 3. Variation of porosity and permeability with temperature and pressure for deep shale samples from Well B1 (dotted lines indicate the recovery curves of porosity and permeability when temperature and pressure decrease). |
3.2. Rock mechanics experiment at high temperature and high pressure
Table 5. Results of triaxial compression-sound wave integration experiment at high temperature and high pressure |
Sample No. | Experimental conditions | Experimental results | |||||||
---|---|---|---|---|---|---|---|---|---|
Confining pressure/MPa | Temperature/°C | Compressive strength/MPa | Peak strain/% | Elastic modulus/GPa | Poisson's ratio | Pre-peak average P-wave velocity/(m·s-1) | Proportion of fracture volume/% | ||
A2-1 | 30 | 80 | 215.2 | 1.49 | 11.62 | 0.181 | 3281.08 | 1.78 | |
A2-2 | 50 | 100 | 240.6 | 1.71 | 12.59 | 0.174 | 3634.80 | 1.59 | |
A2-3 | 70 | 120 | 266.5 | 1.83 | 13.02 | 0.190 | 3654.91 | 1.46 | |
B1-1 | 30 | 80 | 277.3 | 1.65 | 17.02 | 0.192 | 3355.78 | ||
B1-2 | 50 | 100 | 292.8 | 1.91 | 17.80 | 0.181 | 3557.08 | ||
B1-3 | 70 | 120 | 300.9 | 1.99 | 17.74 | 0.183 | 3764.11 | ||
B2-1 | 10 | 60 | 165.3 | 1.27 | 13.24 | 0.181 | 3310.11 | 2.30 | |
B2-2 | 30 | 80 | 326.4 | 1.89 | 16.98 | 0.175 | 3738.01 | 2.21 | |
B2-3 | 50 | 100 | 402.8 | 2.11 | 17.46 | 0.171 | 3920.78 | 2.04 | |
B2-4 | 70 | 120 | 435.1 | 2.18 | 17.56 | 0.168 | 3940.86 | 1.97 |
Fig. 4. Stress-strain curves of deep shale samples from triaxial compression experiment at high temperature and high pressure. |
Fig. 5. Dynamic monitoring of P-wave velocity of siliceous shale samples from Well B2 in triaxial compression experiment at high temperature and high pressure. |
Fig. 6. CT scanning 3D views of siliceous shale after compression in Well B2. (a) Vertical view section, at 80 °C and 30 MPa; (b) Side view section, at 80 °C and 30 MPa; (c) Front view section, at 80 °C and 30 MPa; (d) Vertical view section, at 100 °C and 50 MPa; (e) Side view section, at 100 °C and 50 MPa; (f) Front view section, at 100 °C and 50 MPa; (g) Vertical view section, at 120 °C and 70 MPa; (h) Side view section, at 120 °C and 70 MPa; (i) Front view section, at 120 °C and 70 MPa. |
Fig. 7. CT scanning 3D views of carbonate-bearing siliceous shale after compression in Well A2. (a) Vertical view section, at 80 °C and 30 MPa; (b) Side view section, at 80 °C and 30 MPa; (c) Front view section, at 80 °C and 30 MPa; (d) Vertical view section, at 100 °C and 50 MPa; (e) Side view section, at 100 °C and 50 MPa; (f) Front view section, at 100 °C and 50 MPa; (g) Vertical view section, at 120 °C and 70 MPa; (h) Side view section, at 120 °C and 70 MPa; (i) Front view section, at 120 °C and 70 MPa. |
4. Discussion
4.1. Factors affecting porosity and permeability of deep shale
4.1.1. Effect of experiment on porosity and permeability of deep shale
4.1.2. Limitation of temperature-pressure effect of rock mechanics on porosity and permeability of deep shale
4.1.3. Control of lithofacies and mineral composition difference on porosity and permeability of deep shale
Fig. 8. Porosity and permeability changes of shale samples from Well A1 and Well B1 in the study area under high temperature and high pressure conditions. |