Characterization of Connectivity in Ultra-Deep Fractured-Caveate Reservoirs Considering Fluid-Solid Coupling: A Case Study of the Manfen Block in the Fuman Oil Field of the Tar Basin

doi:10.13745/j.esf.sf.2024.6.33

Abstract

Abstract:

Ultra-deep fractured-cave carbonate reservoirs are buried at great depths, with high stresses, and possess complex and diverse storage spaces. Fluid flow and seepage coexist, making the characterization of reservoir connectivity challenging. Accurate characterization of reservoir connectivity is crucial for identifying oil and gas enrichment areas, predicting reserves precisely, optimizing well patterns, and planning well locations. Therefore, this study focuses on the ultra-deep fractured-cave carbonate reservoirs in the Fuman Oil Field of the Tarim Basin. Considering the effect of fluid-solid coupling, a coupled mathematical model of stress seepage and free flow in fractured-cave reservoirs was established. A systematic study on the connectivity of ultra-deep fractured-cave carbonate reservoirs was conducted using a combination of rock permeability evolution experiments and numerical simulations. The research results indicate that with the increase of confining stress and axial stress, rock permeability gradually decreases, leading to weakened rock connectivity. Under low confining stress conditions, axial stress significantly affects rock permeability and connectivity. As the fracture aperture and angle increase, reservoir connectivity gradually improves. Fracture-connected caves can significantly enhance reservoir connectivity. The fluid flow rate and equivalent permeability increase with the increase in cave volume, which greatly improves reservoir connectivity. However, simply increasing the number of caves weakens the free flow (Stokes) effect, resulting in a less significant improvement in reservoir connectivity. The research findings provide technical support for the precise evaluation of deep carbonate reservoirs and enhance the efficiency of oil and gas exploration and development.

Key words: ultra-deep reservoir, carbonate reservoir, reservoir connectivity, rock mechanical properties, fluid-solid coupling

CLC Number:

CAI Zhenzhong, ZHAO Haitao, WANG Peng, LI Jing, XU Guojin. Characterization of Connectivity in Ultra-Deep Fractured-Caveate Reservoirs Considering Fluid-Solid Coupling: A Case Study of the Manfen Block in the Fuman Oil Field of the Tar Basin[J]. Earth Science Frontiers, 2024, 31(5): 301-312.

Figures/Tables 14

Fig.1 Study area location and top structure map (based on data from PetroChina Tarim Oilfield, 2023)

Fig.2 Experimental instrument and schematic diagram of core permeability test

Table 1 Summary of confining stress and axial stress in core permeability tests under tri-axial stress

轴压/MPa	围压/MPa
0	5	10	20	30	40	50	60	70	80
5	5	10	20	30	40	50	60	70	80
10	5	10	20	30	40	50	60	70	80
15	5	10	20	30	40	50	60	70	80
20	5	10	20	30	40	50	60	70	80
25	5	10	20	30	40	50	60	70	80

Table 2 Core permeability test results under three-way stress

围压/MPa	渗透率/(10^-3 μm²)
围压/MPa	σ=0 MPa	σ=5 MPa	σ=10 MPa	σ=15 MPa	σ=20 MPa	σ=25 MPa
5	0.620 2	0.434 2	0.369 9	0.300 2	0.251 7	0.202 5
10	0.437 8	0.344 1	0.273 4	0.213 0	0.167 5	0.132 1
20	0.287 3	0.221 2	0.182 3	0.130 6	0.093 2	0.065 3
30	0.201 3	0.151 4	0.118 0	0.084 7	0.060 0	0.031 5
40	0.134 3	0.106 0	0.074 7	0.062 5	0.039 4	0.020 8
50	0.095 3	0.075 9	0.060 3	0.049 3	0.037 0	0.020 6
60	0.079 6	0.063 1	0.050 9	0.041 6	0.032 3	0.020 5
70	0.077 9	0.063 0	0.047 0	0.037 7	0.030 2	0.020 3
80	0.077 6	0.063 0	0.048 7	0.037 5	0.030 0	0.020 3

Fig.3 Core permeability test results under tri-axial stress

Fig.4 Flowchart for establishing the coupled mathematical equation of reservoir stress, percolation, and free flow

Fig.5 Schematic diagram of stress of reservoir rock unit

Table 3 Summary of basic parameters of numerical model

参数	孔隙度/%	渗透率/ (10^-3μm²)	泊松比	弹性模量/GPa	基岩密度/ (g·cm^-3)	滑移系数α_BJ
数值	4.3	0.62	0.297	34.18	2.68	1
参数	流体密度/ (g·cm^-3)	动力黏度/ (mPa·s)	最大主应力/MPa	垂向应力/MPa	最小主应力/MPa
数值	0.806	1.725	150	140	130

Fig.6 Dimensions of the numerical model

Fig.7 Numerical simulation results with different frure apertures

Fig.8 Numerical simulation results under different fracture angles a—0°;b—30°;c—45°;d—85°。

Fig.9 Numerical simulation results with different numbers of karst caves

Fig.10 Numerical simulation results under different cave volume fractions

Fig.11 Numerical simulation results of fractured-cave reservoirs

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