Development and distribution pattern of fault-controlled fractures in complex structural deformation zones

doi:10.13745/j.esf.sf.2024.6.20

Abstract

Abstract:

Natural fractures are important reservoir spaces and seepage channels for oil and gas. In complex structural deformation zones, fractures are obviously controlled by faults, but the laws and modes of fracture formation are not yet clear. This study investigates natural fractures developed in complex fault zones in the Kuqa depression. Based on geological observation, fracture interpretation from imaging logging, and theoretical analysis, a “fault-controlled fracture coefficient (K)” is defined and calculated to reveal the development and distribution pattern of fault-controlled fractures in the study area. The results indicate (1) the thrust faults obviously control both the occurrence and development of natural fractures, where the fracture density is exponentially inversely proportional to the distance from the fault, and the fault-controlled fracture zones can be divided into strongly-controlled, weakly-controlled, and regional fracture zones with increasing distance to the fault. (2) Among the strike-slip faults, high-angle oblique faults develop fault-controlled fracture zones where fracture development is significantly affected by the scale of the faults; while fractures associated with oblique thrust faults are mainly developed within the fault zone, and the width of the fault zone varies along the strike direction. (3) The fault-controlled fracture coefficient (K) is defined as the ratio of the width of the strongly-controlled fracture zone to the fault displacement (slip displacement). According to the analysis, the K values of thrust faults in the Kuqa depression ranged between 1.50-1.80, and that of strike-slip faults ranged between 0.125-0.150. The results have both theoretical and practical significance for guiding oil and gas exploration and development in complex structural deformation zones.

Key words: fracture development and distribution pattern, fault-controlled fracture coefficient, strike-slip fault, complex structural deformation zone, Kuqa depression

CLC Number:

JU Wei, YANG Hui, HOU Guiting, NING Weike, LI Yongkang, LIANG Xiaobai. Development and distribution pattern of fault-controlled fractures in complex structural deformation zones[J]. Earth Science Frontiers, 2024, 31(5): 130-138.

Figures/Tables 10

Fig.1 Geographic location, structural units and typical geological section of the Kuqa depression

Fig.2 Field photos of the Tuerlike River fault in the Kuqa depression (a, b) and its associated fractures by geological modeling (c)

Fig.3 Relationship between fracture density and the distance to fault by geological observation (a) and theoretical analysis (b) on natural fractures controlled by the Tuerlike River thrust fault

Fig.4 Diagram showing strike-slip fault types in the Kuqa depression

Fig.5 Field photos of oblique thrust faults (a-c) and high-angle oblique faults (d, e) in the Kuqa depression

Fig.6 Relationship between fracture density and distance to fault by theoretical analysis on nature fractures controlled by the Kudong high-angle oblique fault

Table 1 Parameters used in finite element modeling

地层	ρ/(g·cm^-3)	E/GPa	v	φ/(°)	ψ/(°)	C₀/MPa
N₂k	2.22	10.72	0.25	23	11.50	12.00
N_1-2k	2.25	18.23	0.24	25	12.50	12.80
N₁j	2.25	18.23	0.24	25	12.50	12.80
E	2.08	5.82	0.31	20	10.00	9.80
T-K	2.35	26.62	0.23	32	16.00	16.00
基底	2.40	30.81	0.19	35	17.50	17.00

Fig.7 Numerical simulation results showing the effect of high-angle oblique fault displacement on strain distribution

Table 2 Calculated fault-controlled fracture coefficient (K) values for oblique thrust faults and thrust faults in the Kuqa depression

断层名称	断层性质	断距或滑距/m	断层强控制裂缝带宽度/m	K
塔拉克断层	逆冲-走滑断层	1 000	150	0.150
阿格断层	逆冲-走滑断层	280	40	0.143
库东断层	调节走滑断层	20	2.5	0.125
阳霞煤矿断层	逆冲断层	1.0	1.5	1.500
吐格尔明断层	逆冲断层	0.5	0.8	1.600
克孜勒努尔沟断层I	逆冲断层	20	30	1.500
克孜勒努尔沟断层II	逆冲断层	15	27	1.800
吐尔力克河断层	逆冲断层	32	50	1.563

Fig.8 Proposed development and distribution patterns of fractures controlled by strike-slip faults and thrust faults in the complex structural deformation zones, Kuqa depression

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