鄂尔多斯盆地西缘中段构造特征与油气勘探前景

鄂尔多斯盆地西缘中段是西缘构造带的重要组成部分，关于该区的地下构造模式由于受地下构造复杂与地震资料品质差的影响长期以来缺乏清晰的认识。通过地表地质、大量地震资料的综合研究，纵向上以下古生界类复理石浊积岩系、上古生界煤系区域性滑脱层为界，将该区划分为上部的逆冲推覆构造系统和下部的原地系统。前者断裂、褶皱发育，由6个逆冲席组成，横向分带性特征明显，自西向东划分为逆冲推覆构造主体、前缘过渡带、前缘带三个带；后者构造变形较弱，总体为西倾单斜，局部地区发育完整背斜圈闭。前缘过渡带、前缘带及原地系统勘探目的层众多，油气成藏地质条件好，勘探前景较好；逆冲推覆构造主体目的层已裸露，油气生成与保存条件较差，勘探潜力欠佳。

Structural Features of the Middle Section and Its Petroleum Exploration Prospects in the West Margin of Ordos Basin

The middle section in the west margin of Ordos basin, located between Ordos Block and Qinling-Qi-lianshan fold belt, is an important part of the west margin tectonic belt. Many studies have been carried out about the surface structural features in recent years, but the underground structural features and structural modes are not clear till now due to the complex structural deformation and poor seismic imaging quality making identification of underground structures difficult.Integrated surface geology and a mass of high-quality seismic data, given the decollement from flyschoid turbidites of Lower Paleozoic to coalmeasures of Upper Paleozoic as a detachment, two structural systems can be divided vertically which are the thrust nappe tectonic system in the upper part and the autochthonous system in the lower part. The former is constituted of six thrust sheets with intensive deformation of folds and faults, which are Luoshan thrust sheet, Weizhou thrust sheet, Shigouyi thrust sheet, Yandunshan thrust sheet, Jijiajing thrust sheet and Majiatan thrust sheet, has obvious lateral zonation characteristics and is divided horizontally into three parts from west to east in this area, such as overthrust structural body, frontal transitional zone and front zone. The autochthonous system is a west-dipping monocline with weak structural deformation, and complete anticlinal traps are developed in local area. A greater exploration prospect for oil and gas can be assumed in the frontal transitional zone, the front zone and the autochthonous system due to numerous exploration targets and good geological conditions of hydrocarbon accumulation. The Cambrian to Jurassic exploratory objectives are exposed, together with the intense deformation of faults, the generation and preservation of hydrocarbon become poor, herein making petroleum exploration potential poor in the overthrust structural body.