DF1-1底辟区构造应力场及渗流场演化的数值模拟研究

DF1- 1底辟区是莺歌海盆地内超压流体最活跃的地带之一 .超压流体的活动直接受控于构造应力及其形成的不同类型的断裂和裂隙构成的输导系统 .从底辟区大规模流体垂向活动以及幕式活动的特征来看 ,流体流动的动力主要是由于垂向压差的存在以及渗流场变化引起的局部应力场 (包括热应力场 )的作用所致 .在详细研究底辟区的构造及流体活动关系的基础上 ,对底辟区构造应力场及渗流场的演化进行了模拟 .结果显示 :构造运动引起的应力场决定了DF1- 1底辟区油气沿主要断裂系走向迁移的总趋势 ,在底辟区流体从底辟的两侧向其中心运移 ,由底辟体中向上运移为主 ;高压流体产生的热应力控制局部应力场状况及油气运移方向 ,驱动流体向底辟体顶部运移 ,当热应力值过大时有可能改变应力场状况以及油气运移总趋势 .

Digital Simulation of Structural Stress Field and Flow Field in DF1-1 Diapir

DF1-1 diapir is one of the most active areas with the overpressure fluid in Yinggehai basin. The overpressure fluids were controlled by the structural stress and migration system made up of different types of fractures and faults. In terms of the large-scale vertical and episodic fluid flows in the diaper area, the dynamics of the fluid flows is mainly attributed both to the vertical pressure difference and to the local stress fields (including thermal stress field) caused by the changes in infiltration flow field from fluid flow. The relationship between structure and fluid flow in the diaper area thus obtained in this paper is employed to simulate, together with the finite element digital method, the evolutions of both the structural stress fields and the infiltration fluid filed that are in line with the process of diapirism. The results show that the stress fields and fluid migration fields before diapirism are different from those after it. As a whole, stress fields from the tectonic stress determined the fluid migrating pattern along the fault zone in the DF1-1 diapir, that is, the fluids migrating from both sides of the diapir to its center and migrating upward from the diapir. Thermal stresses caused by the high-pressure fluid flow also controlled the local stress pattern and petroleum and gas fluid flow direction, which drove the matured hydrocarbon fluid migration upward from depression to highland. Too great a thermal stress value might have changed the stress pattern and the general trend of the petroleum and gas migration.