川东北达川—万县地区下三叠统飞仙关组层序地层研究

Characteristics of sequence stratigraphy of the Lower Triassic Feixianguan Formation in Dachuan-Wanxian area,northeastern Sichuan Basin

为了厘清达川—万县地区下三叠统飞仙关组鲕滩储层和白云岩储层的发育、演化及纵向分布规律,基于Vail层序地层学理论,以沉积暴露面、岩性突变面和不整合面等多种层序界面标志为依据,对典型单井进行层序划分,再结合相对海平面的升降变化,将飞仙关组划分为2个三级层序(Sq1和Sq2)及4个体系域(Sq1海侵体系域、Sq1高位体系域、Sq2海侵体系域和Sq2高位体系域),进而通过跨相区连井层序地层剖面的对比,建立了该区层序地层格架。研究表明,各体系域在区域上可对比性较强,高位体系域后期发育台地边缘鲕滩相和台地内鲕滩相沉积,且均发生了强烈的白云岩化作用,改善了岩石孔渗性;在深埋藏条件下,白云岩原生孔隙易于保存,具有一定抗压实、压溶性,为深层优质储层的形成奠定了基础。研究结果可为该区下一步天然气勘探开发提供一定地质依据。

In order to clarify the development, evolution and distribution of oolitic beach reservoir and dolomite reservoir of the Lower Triassic Feixianguan Formation in Dachuan-Wanxian area, based on the theory of Vail sequence stratigraphy, combined with sequence boundary markers, such as the exposed surface, lithological mutation and sequence unconformity surface, the sequence of the typical single well was divided. According to the change of relative sea level rising and falling, the Feixianguan Formation can be divided into two third-order se- quences （Sql and Sq2） and four system tracts. Sql consists of the first and second members of Feixianguan Formation, and Sq2 consists of the third and fourth members of Feixianguan Formation. Both Sql and Sq2 are made up of transgressive and highstand systems tracts, lacking of the lowstand systems tract. The sequence stratigraphic framework of this area was established by comparing the sequence stratigraphic sections of the cross facies zone. The results show that each systems tract in the region can be comparative, platform margin oolitic facies and intra- platform oolitic facies developed in the late period of highstand systems tract, and the strong dolomitization im- proved the porosity and permeability. Under the condition of deep burial, the primary pore of dolomite is easy to be preserved, and it has a certain anti-compaction and anti-pressure solution, which lays a foundation for the formation of high quality reservoir. The result has important geological significance for further exploration in Sichuan Basin.