鄂尔多斯盆地榆林－神木地区上古生界裂缝和断层分布及其对天然气富集区的影响

鄂尔多斯盆地东部榆林-神木地区上古生界发育了断层和3种类型的裂缝.裂缝类型有区域构造缝、水平缝（包括层理缝与缝合线）和成岩缝,其中,区域构造缝主要呈北东向分布,在上古生界各层位均发育,缝合线在山2段中下部和太原组灰岩中都可见到,层理缝仅见于山西组山2段中下部,成岩缝仅见于石千峰组千5段.断层为逆断层,断穿了上古生界下部气藏的区域盖层和烃源岩.裂缝和断层分布对研究区重点勘探层位山2段、盒8段和千5段的天然气富集起到了重要作用：伴生的层理缝和缝合线的分布控制了山2段天然气富集区;区域构造缝的分布促进了盒8段天然气的富集;而千5段天然气的富集则依赖于本区断穿上石盒子组的断层和区域构造缝的分布.图6表2参29

Fractures and faults distribution and its effect on gas enrichment areas in Ordos Basin

Faults and three kinds of fractures are found from the upper Paleozoic strata in the Yulin-Shenmu region of the eastern Ordos Basin.The fractures consist of regional structure fractures,horizontal fractures(including bedding fractures and stylolites) and diagenic fractures.The regional structure fractures mainly extending along the northeast direction appear in all the strata of upper Paleozoic.The stylolites exist in the middle-lower parts of the second Member of Shanxi Formation(Shan 2) and carbonates of Taiyuan Formation.The bedding fractures are only seen in the middle-lower parts of Shan 2 and the diagenic fracures only in the fifth Member of Shiqianfeng Formation(Qian 5).The faults belong to inverse faults and break through the regional cover and source rocks of the lower gas reservoir of upper Paleozoic.The distribution of faults and fractures plays an important role in the gas accumulation of the three key reservoirs of Shan 2,Qian 5 and the eighth Member of Shihezi Formation(He 8),of which,the coexisting bedding fractures and stylolites control the distribution of gas enrichment area of Shan 2,regional structure fractures contribute to the gas enrichment for He 8,and the gas enrichment for Qian 5 depends on the distribution of faults breaking through the upper Shihezi Formation and regional structure fractures.