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Development characteristics and orientation of tight oil and gas in China
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SUN Longde,ZOU Caineng,JIA Ailin,WEI Yunsheng,ZHU Rukai,WU Songtao,GUO Zhi
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Table 1 Three-level evaluation system for tight oil sweet spots.
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Sweet spot
area | Lithology | Physical property | Oil-bearing property | | Reservoir effective thickness/m | Thickness ratio of re-
servoir to stratum/% | Shale
content/
% | Area/
km2 | Depth/
m | Porosity/% | Overburden pressure
permeability/
10-3 μm2 | Oil
satura-
tion/% | Surface oil density/
(g·cm-3) | Gas-oil
ratio | | Sandstone | Carbonate | Sand-
stone | Carbo-
nate | | Level I | >15 | >80 | >70 | <15 | >50 | <3 500 | >12 | >7 | >0.1 | >65 | <0.75 | >100 | | Level II | 10-15 | 75-80 | 60-70 | 15-20 | 50-30 | 3 500-4 500 | 8-12 | 7-4 | 0.01-0.1 | 50-65 | 0.75-0.85 | 10-100 | | Level III | 5-10 | 70-75 | 50-60 | 20-30 | <30 | >4 500 | 5-8 | 4-1 | 0.001-0.01 | 40-50 | 0.85-0.92 | <10 | Sweet spot
area | Source rock | Brittleness index | Crustal stress | | Effective thickness/m | Organic
matter type | TOC/
% | Ro/
% | Area/
km2 | Poisson’s
ratio | Elasticity modulus/
104 MPa | Horizontal 2-direction
principal stress times | Pore pressure
coefficient | | Level I | >20 | I, II1 | >2 | 0.9-1.1 | >300 | <0.2 | >3 | About 1 | >1.2 | | Level II | 15-20 | Mainly II1 | 1-2 | 0.8-0.9 | 150-300 | 0.2-0.3 | 2-3 | 1-1.5 | 1.0-1.2 | | Level III | 5-15 | Mainly II2 | 0.5-1.0 | 0.6-0.8 | <150 | 0.3-0.4 | 1-2 | 1.5-2 | 0.8-1.0 |
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