天然裂缝是油气重要的储集空间和渗流通道。在复杂构造变形区,裂缝明显受断层影响控制,但其规律和模式尚不清晰。为此,本次研究以库车坳陷为例,通过现场地质观测、成像测井裂缝解译和理论分析,计算断控裂缝系数,揭示走滑断层、逆冲断层控制复杂构造变形区天然裂缝的规律,提出断控裂缝发育分布模式。结果表明:(1)逆冲断层对天然裂缝产状和发育程度均具有明显的控制作用,裂缝密度与距断层距离呈现负指数关系,距断层由近及远可以划分为断层强控制裂缝带、断层弱控制裂缝带和区域裂缝带。(2)走滑断层包括调节走滑断层和逆冲-走滑断层。调节走滑断层与地层走向近垂直或大角度斜交,发育断层控制裂缝带,其受断层规模影响显著;逆冲-走滑断层与地层走向近平行或者小角度斜交,天然裂缝主要局限于断层带内,沿断层走向断裂带宽度发生变化。(3)定义断控裂缝系数(K),即断层强控制裂缝带宽度与断层断距(滑距)的比值,通过分析,库车坳陷逆冲断层K值为1.50~1.80,走滑断层K值为0.125~0.150。研究成果对复杂构造变形区油气勘探开发具有理论和实践指导意义。

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.