川西龙门山推覆构造特征及有利油气勘探区块预测

NAPPE STRUCTURE CHARACTERISTICS AND EXPLORATION POTENTIAL FORECAST IN LONGMENSHAN,THE WEST OF SICHUAN PROVINCE

川西龙门山推覆构造带平面上可划分为3段,北段属印支期褶皱,中段属燕山期褶皱,南段属喜山期褶皱;纵向上可分为3层,下层为印支期原地系统,中层为燕山期推覆构造,上层为喜山期推覆和滑移叠加构造。龙门山构造带经过多期次构造运动,形变强烈,因此,封盖保存条件是成藏的关键因素。北段断层通天,目的层裸露;中段目的层裸露与掩盖参半;南段地表出露中下侏罗统红层,发育连续形变对破裂构造的封盖,目的层埋深适中,油气藏保存条件变好。据此认为龙门山南段的大邑、高家场—莲花山构造带是最有利地带,可以找到大、中型油气田;中段的磁丰场—亍子断褶带是有利地带,可望找到中、小型油气田;北段油气藏破坏,局部地段可能发现小型残余稠油藏。进而提出在山前隐蔽带首钻大邑、重上鸭子河、探索金马、聚源的部署建议。

The Longmenshan nappe structure in the west of Sichuan Province can be divided into three parts in plane： the Indosinian fold in the north, the Yanshanian fold in the middle and the Himalayan fold in the south. There are 3 layers vertically： the Indosinian autochthon at the bottom, the Yanshanian nappe structure in the middle and the Himalayan gliding nappe and superposition at the top. The Longmenshan structure has undergone multiple-epoch structural movements with strong deformation, thus its sealing conditions of preservation are the key factor to form reservoirs. In the north, faults are cut through and objective intervals are exposed, thus oil and gas reservoirs are destroyed. In the middle, objective intervals are exposed and sealed half-and-half and the preservation condition is general. In the south, the Middle and Lower Jurassic red bed, which is exposed to surface, develops continuous deformation resulting in seal to the fractured structure, thus the preservation condition has been improved. Hereby, it is concluded that the structural belt from Gaojiachang to Lianhuashan in the southern Longmenshan is the most favorable zone in which large and medium oil and gas fields may be discovered. The fault-fold zone in the middle is the favorable zone in which medium and small oil and gas fields may be found. Oil and gas reservoirs in the north have been destroyed in which small residual heavy oil and gas reservoirs may be discovered. In addition, Dayi, Yazihe, Jinma and Juyuan in the subtle area of the front of mountain should be paid more attention to.