鄂尔多斯盆地延长组致密油特征

Characteristics of tight oil in Triassic Yanchang Formation,Ordos Basin

通过综合研究鄂尔多斯盆地延长组致密油储集层与烃源岩展布、岩石学、地球化学等资料,分析鄂尔多斯盆地延长组致密油特征,评价其勘探潜力。鄂尔多斯盆地中生界延长组低渗透油气资源丰富,截至目前空气渗透率小于2×10 3μm2的致密油探明地质储量约20×108t,主要赋存于与油页岩互层共生或紧邻的延长组长6—长8油层组致密砂岩储集层中,石油未经过大规模长距离运移。其中,湖盆中部长7和长6油层组大面积分布的重力流砂岩储集层尤其致密,空气渗透率一般小于0.3×10 3μm2。延长组致密油具有多成因砂体复合叠加规模大、储集层致密、孔喉结构复杂、刚性组分含量高、裂缝发育、含油性和原油物性较好、低压低产等特征。优质烃源岩与大面积厚层储集体互层共生,以及地史期生烃增压强排烃作用控制了延长组大面积叠合致密油的形成。鄂尔多斯盆地致密油资源潜力大,是近期建产的现实目标和未来勘探开发的重要领域。

By comprehensive study of reservoir and source rock distribution, petrology and geochemistry, the tight oil and its exploration potential was analyzed in the Triassic Yanchang Formation, Ordos Basin. The Triassic Yanchang Formation is rich in low permeability reservoirs. The proved geological reserves of tight oil, with the permeability less than 2×10^-3μm^2, is about two billion tons by now. The tight oil mainly occurs in tight sandstone reservoirs of Chang6-Chang8 oil-bearing members which are close to or interbedded with the oil shale layers, without long-distance migration. The large-scale gravity flow sandstone reservoirs of Chang7 and Chang6 oil-bearing members in the center of the lacustrine basin are particularly tight, with the permeability less than ×10^-3μm^2 in general. The tight oil in the Yanchang Formation features large scale in sand body complex, tight reservoir, complicated pore throat structure, high content of rigid components, abundant fractures and saturation, good crude property, low fluid pressure and low oil yield. The formation of large-scale superimposed tight oil reservoirs is controlled by the interbeded lithologic combination of extensive source rocks and reservoirs and the strong hydrocarbon generation and expulsion during geological history. This type of pools is an important potential resource for future oil exploration and development.