川东北宣汉—达县地区晚中生代—新生代构造应力场转化及其油气意义

Transition of tectonic stress field and hydrocarbon significance of the Late Mesozoic-Cenozoic in Xuanhan-Daxian region,northeastern Sichuan Basin

构造应力是地壳中较为活跃的能量之一,构造应力作用方式和转变形式的研究对油气藏勘探开发有重要的指导意义。通过研究直立褶皱、共轭节理、断裂面擦痕等各种构造形迹,重建宣汉—达县地区晚中生代—新生代构造应力场,分析其构造活动规律。燕山晚期,川东构造带自SE方向的扩展影响到宣汉—达县地区,形成一系列NE向断裂和褶皱;喜马拉雅期,川东构造带逐渐趋于平静,大巴山构造自NE方向挤压,造就NW向断裂和褶皱的形成。不同方向、时期、强度的构造应力场叠加控制了研究区油气藏的形成和演化,阶段性的构造活动对研究区的叠加作用改善了储集层物性,较好地控制了圈闭的发育,将岩性油气藏调整为构造-岩性复合控制的油气藏,同时产生的构造应力和岩石中形成的裂缝分别为油气运移提供动力和通道。

Tectonic stress is one of the comparatively active energies in the earth＇s crust. It is of guiding significance in oil and gas ex- ploration and development to study tectonic stress patterns and transformation processes. Through studies on upright folds, conju- gate joints, slickenside on fracture planes and other structural vestiges, we rebuilt the Late Mesozoic-Cenozoic tectonic stress field of Xuanhan-Daxian region and examined regular patterns of its tectonic activities. The result shows that this region experienced at least two tectogeneses in Late Mesozoic-Cenozoic, one occurred during Late Yanshanian, when a series of NE-direction faults and folds de- veloped in Xuanhan region of east Sichuan under the SE to NW direction compression; and the other happened in Himalayan period, when the east Sichuan tectonic belt subsided gradually while NW-direction faults and folds were formed by the NE to SW direction extrusion in Daba mountain. The superposition of various tectonic stress fields with different directions and intensities in different pe- riods comprehensively controlled the formation and evolution of oil and gas reservoirs of this region. The superimposition of stag- gered tectonic activities in the study area has improved reservoir properties, substantially controlled the development of hydrocarbon traps and adjusted lithologic reservoirs into structural-lithologic composite ones. Moreover, tectonic stress and fractures formed con- sequently in rocks have provided oil and gas migration with dynamic power and pathways.