库车坳陷克拉苏冲断带传递型超压的识别、计算及其主控因素

超压可在断裂的沟通作用下发生垂向传递,目前对于断裂传递型超压的识别、计算和预测研究还比较薄弱。分析此类超压的成因,修正前人关于垂向传递型超压识别方法,以库车坳陷克拉苏冲断带盐下断裂发育的超压地层为例,通过含气声速校正和浮力校正,识别盐下断裂传递型超压,近似计算传递量,最终分析影响该区断裂传递超压量的主控因素。结果表明:克拉苏冲断带的大北和克拉苏地区的盐下地层均不同程度存在超压传递现象;超压的传递量在大北地区大北3井为24.10 MPa,在吐北2井为26.35 MPa,克拉苏地区的克拉2井平均为16.47 MPa,由断裂传递所产生的超压约占实测总过剩压力的50%;超压的传递量主要受断裂的断距、倾角及断裂穿越地层的过剩压力梯度的综合影响,是三者乘积的综合效应。

Identification, calculation and main controlling factors of overpressure transferred by fault in Kelasu thrust belt of Kuqa depression

Overpressure can be transferred vertically by fault. Studies of identification, calculation and prediction of overpressure transferred by fault, however remain currently underdeveloped. The origin of this type of overpressure was analyzed, and earlier identification methods of the overpressure were modified. Taking an example of the fault development stratum bearing overpressure under salinastone in Kelasu thrust belt of Kuqa depression, overpressure transferred by fault was identified under salinastone after applying corrections due to acoustic velocity by gas bearing and buoyancy. The amount of transferred overpressure was calculated. Finally, the major controlling factors of transferred overpressure were analyzed in the study area. The results show that variable degrees of overpressure transferred by fault exist in Dabei and Kelasu area of Kelasu thrust belt. The amount of overpressure transferred by fault is about 24.10MPa in well Dabei 3,6.35MPa in well Tubei 2, and 16.47MPa in well Kela 2. The overpressure transferred by fault accounts for 50percent of the total measured overpressure, and is mainly influenced by multiplied effects of fault throw, fault dip angle and overpressure gradient in the stratum cut by faults.