库车坳陷应力状态转换特征及其地质与力学响应

Characteristics of stress state transitions and its geological and mechanical response in the Kuqa Depression

结合最新的钻井、测井和地震资料,采用数值模拟手段,明确了塔里木盆地库车坳陷喜马拉雅晚期古应力状态转换特征。通过有限元数值模拟方法揭示了库车坳陷克拉苏构造带巴什基奇克组喜马拉雅晚期应力场三维分布并准确地厘定了古应力状态。通过分析古应力状态与宏观构造样式、裂缝产状及储层物性的关系,系统揭示了古应力状态转换的地质与力学响应,最后利用离散元数值模拟,揭示了古应力状态转换对储层物性的影响机制。综合分析认为:研究区在喜马拉雅晚期6500~7500 m的深度区间逐渐由逆冲型应力场转换为走滑型应力场;6500 m之上为逆冲型应力场,压实减孔量随埋深增大而增大,应力状态与岩石强度均不利于裂缝发育;7500 m之下为走滑型应力场,有利于储层孔隙保存和岩石破裂成缝。研究结果深化了对库车坳陷构造、储层和岩石力学性质的认识,并认为古应力状态转换是克拉苏构造带超深部储层具备形成大中型油气田的力学基础,其发现对克拉苏构造带下一步的油气勘探、开发具有指导意义。

Combined with the latest drilling,logging and seismic data we carry out numerical simulation to better understand the characteristics of the late Himalayan paleostress evolution in the Kuqa Depression,Tarim Basin.Using finite element numerical simulation method we obtained the three-dimensional distribution of the late Himalayan stress field in the Bashijiqike Formation in the Kelasu tectonic belt whereby accurately determined the paleostress state.By analyzing the relationship between the paleostress state and macrostructural style,fracture occurrence and reservoir physical properties,the geological and mechanical response to the paleostress state transition was systematically revealed.Finally,the influece mechanism between the paleostress state transition and reservoir physical properties was revealed by means of discrete element numerical simulation.During the late Himalayan,the stress field gradually transformed from a thrust-type stress field to a strike-slip type stress field at a depth range of 65007500 m.Above 6500 m depth,under thrust stress field,the compaction hole reduction increased with increasing burial depth,and the stress state and rock strength were not conducive to the development of fractures.Below 7500 m depth,the strike-slip stress field was conducive to the preservation of reservoir pores and rock fracturing.The above results deepen the understanding of the tectonic settings,reservoir properties and rock mechanical properties of the Kuqa Depression,suggesting the paleostress state transition provided the mechanical basis for the formation of large and medium-sized oil and gas field in the ultradeep reservoir of the Kelasu tectonic belt.This discovery has guiding significance for the next stage oil and gas exploration and development in the Kelasu tectonic belt.