Introduction
1. Experimental methods and samples
Table 1. Sample parameters for NMR-DP physical simulation |
Basin | Well | Sample No. | Depth/ m | Formation | Length/ cm | Lithology | Diameter/ cm | Porosity/ % | Permeability/ 10−3 μm2 | Fracture development |
---|---|---|---|---|---|---|---|---|---|---|
Qijia-Longhupao areas in the Songliao Basin | G708 | G708-B | 1989.50 | Qingshankou Formation | 3.010 | Siltstone | 2.50± 0.02 | 13.66 | 0.040 0 | Undeveloped |
G72 | G72-B | 2017.50 | 3.571 | 18.03 | 15.858 0 | Penetrating fractures developed | ||||
G93 | G93-A | 2052.66 | 3.096 | 10.48 | 0.086 8 | Relatively developed | ||||
J37 | J37-A | 1852.61 | 4.150 | 17.00 | 3.280 0 | Developed | ||||
J44 | J44-B | 2147.75 | 2.540 | 9.40 | 0.911 4 | Developed | ||||
G921 | G921-D | 1909.81 | 3.600 | 10.95 | 1.154 4 | Developed | ||||
J392 | J392-C | 1824.70 | 3.681 | 13.71 | 0.060 2 | Undeveloped | ||||
J393 | J393-D | 1950.35 | 4.216 | 4.41 | 0.016 5 | Undeveloped | ||||
J191 | J191-E | 1838.11 | 3.240 | 6.45 | 0.022 5 | Undeveloped | ||||
T234 | T234-A | 1772.30 | 3.590 | 16.26 | 1.830 0 | Developed | ||||
T234 | T234-B | 1771.18 | 3.927 | 11.88 | 0.214 9 | Relatively developed | ||||
L29 | L29-B | 1918.92 | 3.050 | 14.46 | 0.066 6 | Underdeveloped | ||||
L23 | L23-B | 1882.00 | 3.244 | 9.41 | 0.067 7 | Underdeveloped | ||||
Santanghu Basin | Ma56 | M56-3 | 2142.80 | Tiaohu Formation | 5.575 | Tuff | 2.50± 0.02 | 27.62 | 0.184 5 | Impenetrable |
Ma56-12H | M56H-4 | 2130.82 | Tiaohu Formation | 3.127 | Tuff | 14.74 | 0.141 0 | Impenetrable | ||
Ma702 | M702-3 | 1818.80 | Tiaohu Formation | 3.836 | Tuff | 9.25 | 13.190 0 | Penetrating fractures developed | ||
Tiao25 | T25-1 | 1157.48 | Tiaohu Formation | 2.240 | Basalt | 9.11 | 0.028 5 | Underdeveloped | ||
Ma56 | M56-6 | 2668.50 | Lucaogou Formation | 3.853 | Mixed rock | 4.54 | 0.034 2 | Underdeveloped |
2. Tight oil charging, migration and accumulation in continental lake basins
2.1. The dynamic forces driving hydrocarbon generation and expulsion of high-quality source rocks are the foundational power that determines the charging efficiency and accumulation of tight oil
Fig. 1. Effect of charging power on tight oil charging, migration and accumulation (sample number: M56H-4). |
2.2. Oil migration resistance is a crucial factor affecting the charging efficiency and accumulation effect of tight oil
Fig. 2. Physical simulation of the effect of pore structure on tight oil charging and accumulation. (a) Nuclear magnetic signal change during the displacement of signaled formation water with non-signaled fluorine oil, sample T234-A; (b) Changes of oil saturation and pressure gradient during charging, sample T234-A; (c) Distribution of initial saturated water, bound water and charged oil (saturated water-bound water) after charging, sample T234-A; (d) Nuclear magnetic signal change during the displacement of signaled formation water with non-signaled fluorine oil, sample L23-B; (e) Changes of oil saturation and pressure gradient during charging, sample L23-B; (f) Distribution characteristics of initial saturated water, bound water and charged oil (saturated water-bound water) after charging, sample L23-B. |
Fig. 3. Influence of pore structure on tight oil charging and accumulation by Lattice Boltzmann physical simulation. (a) Three-dimensional pore characterization by micro-CT, sample T234-A; (b) Three-dimensional pore-throat connection, sample T234-A; (c) Simulated charging process of tight oil, sample T234-A; (d) Three-dimensional pore characterization by micro-CT, sample M56-6; (e) Three-dimensional pore-throat connection, sample M56-6; (f) Simulated charging process of tight reservoir oil, sample M56-6. |
Fig. 4. Effect of micro-fractures on tight oil charging and accumulation by physical simulation on tuff samples of Tiaohu Formation in the Santanghu Basin. (a) Nuclear magnetic signal change during the displacement of signaled formation water with non-signaled fluorine oil, sample M56-3, microfractures perpendicular to the direction of charge; (b) Nuclear magnetic signal change during the displacement of signaled formation water with non-signaled fluorine oil, sample M56H-4, without microfractures; (c) Nuclear magnetic signal change during the displacement of signaled formation water with non-signaled fluorine oil, sample M702-3, microfractures parallel to the direction of charge; (d) Changes of oil saturation and pressure gradient during charging of fluorine oil, sample M56-3 ; (e) Changes in oil saturation and pressure gradient during charging of fluorine oil, sample M56H-4; (f) Changes in oil saturation and pressure gradient during charging of fluorine oil, sample M702-3. |
2.3. The coupling effect of charging force and pore throat resistance of tight reservoir controls tight oil accumulation and sweet spot enrichment
Fig. 5. Effect of reservoir physical properties on oil saturation. |
3. Controlling factors on tight oil enrichment in continental lake basins
3.1. High-quality source rocks control the near-source distribution of tight oil
Fig. 6. Hydrocarbon generation intensity and distribution of oil wells sourced from Jurassic source rocks in the Sichuan Basin. |
Fig. 7. Relationship between annual production of the single well and source rock thickness in Jurassic Da'anzhai Member in the Sichuan Basin. |
3.2. The physical properties and pore size of reservoir are positively correlated with the degree of tight oil enrichment
Fig. 8. Relationship between reservoir physical properties and flow characteristic parameters and oil saturation. |
Table 2. Saturation of samples with different physical properties |
Sample | Porosity/ % | Permeability/ 10−3 μm2 | Pore volume/cm3 | Saturation/ % |
---|---|---|---|---|
B | 11.80 | 0.040 | 1.34 | 62 |
D | 12.92 | 0.012 | 1.47 | 41 |
E | 10.20 | 0.010 | 1.16 | 26 |
3.3. The anisotropy of reservoir structure reveals that the parallel migration rate is the highest
Fig. 9. Relationship between starting pressure gradient and flow rate in laminated fine sandstone samples of the Chang 7 Member, Ordos Basin. |
3.4. Fractures in the layer improve the migration and accumulation efficiency and oil saturation
Fig. 10. Relationship between charging pressure and oil saturation of the tight reservoir in the Qingshankou Formation in the Songliao Basin. |
Fig. 11. Relationship between cumulative production and fracture development of single oil wells in G oilfield (according to Ref. [9]). |