莺歌海盆地东方1-1底辟区深部热流体穿层的热应力及其效应

Thermal Stresses and Their Effects during the Deep Hot Fluids Penetrating upward in DF 1-1 Diapiric Area, Yinggehai Basin

东方 1 - 1底辟区的热流体活动相当强烈和频繁 .深部热流体的穿层上涌产生热应力造成了局部的应力场状况的变化 ,形成了特征性的构造和断裂系统 ,水力破裂、热流体拱张形成褶皱和局部破裂等 ,这些褶皱和断裂共同构成了底辟带热流体活动中垂向输导的主要通道之一 .由于热流体穿层活动不仅携带了大量的烃类气和CO2 等非烃气 ,而且具极强的热力作用 ,引起了强烈的热异常 ,导致所穿入的浅部地层中的热力学参数 ,如粘土矿物的演化、储层中流体包裹体以及岩石所含有机质的镜质体反射率等发生一系列的异常变化 ,致使底辟作用前后底辟体内部及其围岩的特征具有非常显著的差别 .本次研究对热流体穿层所引起的热应力效应和温度异常采用Field模型进行了定量动力学模拟 ,结果显示应力场和温度场的分布随着时间不断向上迁移 ,使各小断裂和裂隙连通形成流体的良好的垂向运移通道 ,在热流体活动的通道附近热应力的影响十分明显 。

The hot fluids are intensive and frequent in the DF1-1 diapiric area, Yinggehai basin, South China Sea. Thermal fluids penetrating the strata from the deep belt generated thermal stress, which resulted in changes to the local stress field. Moving thermal fluids are capable of transporting a large amount of heat from the deep part of the basin, resulting in thermal anomalies, which heat and expand adjacent sediments to form local thermal stress. Thermal stresses controlled the stress patterns and direction of overpressure fluid migration in some locations. The structural stress associated with thermal stress induced the fluid migration system including fractures, faults and sand folds. On the other hand, because the fluids have had thermal energy and hydrocarbon or CO2 when penetrating strata from the deep, the obvious temperature differentia caused abnormal phenomena in a series of geochemical parameters, including transferring from smectite to illite, vitrinite reflectance rate, the temperature of fluid inclusions etc.. All those processes mean that the characteristics of the diapiric body and its surrounding rock are extremely different before diapirism and after diapirism. This research also demonstrates and analyzes the evolutional process of the thermal stress field and temperature field by comparing a quantitative dynamic simulation with field analysis. The results show that stress fields and temperature fields moved upwards over time. The thermal stress field also promoted the episodic opening of faults, and accelerated the hydrocarbon-bearing fluid flow upwards. The extent of the effect of thermal fluids depends on the proportion between thermal stress and tectonic stress.