西昆仑山前柯深—柯东地区断裂传递型超压的识别与计算

西昆仑山前柯深—柯东地区断裂构造活动剧烈，在浅部地层中存在压力系数高达2.1的极高超压，对于这种超压分布特征和形成机制的研究和认识对钻井工程和油气运移研究具有十分重要的意义。综合储层实测压力、间接估算的泥岩地层压力以及超压地层岩石力学与物性的关系等资料，并结合研究区断裂发育条件和油气运移史，分析了地层压力分布特征和主控机制。结果表明，西昆仑山前柯深和柯东两地区在古近系—白垩系储层中各自形成了相对统一的异常压力系统，系统内地层压力向深部以静水压力梯度增加，储层压力大于附近泥岩压力。研究区储层压力分布特征与深部流体沿开启性断裂的向上传递密切相关。在此基础上，估算了压力传递量，并探讨了影响压力传递量的地质因素。柯深和柯东地区断裂传递增压量分别为15.0～34.0 MPa和8.1～16.5 MPa,与实测总剩余压力的比值分别为24.2%～67.2%和23.4%～53.7%。两个地区断裂传递增压量的差异主要受断裂发育及其与地层的空间配置关系的影响。

Identification and calculation of overpressure transferred by fault in the Keshen- Kedong areas in the piedmont of the western Kunlun Mountains

The recent tectonic activity, in the Keshen- Kedong areas in the piedmont of the western Kunlun Mountains, is intense, and there is a very high overpressure with a pressure coefficient of 2.1 in the shallow sequences. The research and understanding of the distribution and mechanism of this overpressure is of great significance for the study of drilling engineering and hydrocarbon migration. Based on the data of measured reservoir pressures, ones estimated from mudstone and the relationship between rock mechanics and physical properties, the distribution characteristics and main control mechanism of formation pressure are analyzed, combined with fault development conditions and hydrocarbon migration history in the study area. The results show that the Paleogene- Cretaceous reservoirs form a relatively unified abnormal pressure system. The formation pressure in this system increases with a hydrostatic pressure gradient, and the reservoir pressure is greater than the neighbouring mudstone. The reservoir pressure distribution are closely related to the upward transmission of deep fluid along the open faults. Finally, the overpressures transfer by fault is estimated, and the related geological factors are discussed. The ratios of the fault transmitted pressure to the measured total overpressure in Keshen and Kedong areas are 24.2%~67.2% and 23.4%~53.7%, respectively. The difference of transferred amount between the two areas is controlled by fault development and its spatial relationship with the formation.