鄂尔多斯盆地延长组7段3亚段页岩型页岩油储层特征及勘探方向

鄂尔多斯盆地三叠系延长组7段(长7段)泥页岩发育,针对其内部富集的页岩型页岩油尚未取得勘探进展,仅在少量直井的试油阶段突破出油关,但试采效果整体较差。系统梳理了长7段3亚段(长7₃亚段)泥页岩的岩石学、地球化学和储层特征,优选页岩型页岩油的富集有利参数,明确了其成藏条件、勘探方向及潜力。相较于暗色泥岩,长7₃亚段的黑色页岩表现为多类型纹层频繁发育、有机质丰度高、生油母质类型好、主生烃期早、含油率高的特征,是页岩型页岩油勘探的有利岩性。受水平页理缝和陆源长英质、凝灰质等相对高孔高渗纹层的复合影响,黑色页岩的水平渗透率普遍高于垂直渗透率。长7₃亚段泥页岩的储集空间以刚性矿物支撑的粒间孔、粒内溶蚀孔、黏土矿物晶间孔及黄铁矿晶间孔为主,页理缝和超压微裂缝较发育。"有机质+陆源长英质纹层"、"有机质+凝灰质纹层"二元纹层组合与页理缝构成的复合单元对页岩油赋存最为有利。总有机碳(TOC)含量为4%~14%、镜质体反射率R_o>0.8%、页理及纹层发育、脆性矿物含量高的长英质黑色页岩是长7₃亚段页岩型页岩油的有利勘探目标,黑色页岩厚度相对较大、有机质丰度适中的马岭—华池深洼区是页岩型页岩油勘探的Ⅰ类有利区。鄂尔多斯盆地长7₃亚段页岩型页岩油资源丰富,有望成为盆地非常规石油勘探开发的现实性重大战略接替新领域。

Reservoir characteristics and exploration direction of pure shale-type shale oil in the 3rd sub-member, 7th Member of Yanchang Formation in Ordos Basin

Mudstone and shale are developed in 7th Member of the Triassic Yanchang Formation in Ordos Basin, and there is no progress in the exploration of pure shale-type shale oil enriched inside. Oil has been produced only from a few vertical wells in the well testing stage, and the overall pilot production effect is poor. The paper systematically summarizes the petrological, geochemical and reservoir characteristics of mud shale in the 3rd sub-member of 7th Member of Yanchang Formation (Chang 7₃ sub-member), optimizes the favorable parameters for the enrichment of shale type shale oil, and determines its hydrocarbon accumulation conditions, exploration direction and potential. Compared with dark mudstone, the black shale in Chang 7₃ sub-member is characterized by frequent development of multi-type laminae, high abundance of organic matters, good type of parent material of source rock, early main hydrocarbon generation stage and high oil content, which are favorable lithologies for the exploration of pure shale-type shale oil. The horizontal permeability of black shale is generally higher than its vertical permeability due to the complex effect of horizontal lamellation fractures and high porosity and high permeability laminae such as terrigenous felsic and tuffaceous sandstone. The reservoir space of mud shale in Chang 7₃ sub-member is mainly composed of intergranular pores, intragranular denudation pores, clay mineral intercrystalline pores and pyrite intercrystalline pores supported by rigid minerals; lamellation fractures and overpressure microfractures are developed. The composite element composed of the binary laminae combination of "organic matters+terrigenous felsic lamina" and "organic matters + tuffaceous lamina" and lamellation fractures is the most favorable for the occurrence of shale oil. Black felsic shale with the total organic carbon (TOC) content of 4 % ~14 % , vitrinite reflectance R_o>0.8 % , development of lamellation and laminae as well as high content of brittle minerals is a favorable exploration target for pure-shale type shale oil in Chang 7₃ sub-member. The Maling-Huachi deep depression area with thick black shale and moderate organic matter abundance is a Class I favorable area for exploration of pure shale-type shale oil. The Chang 7₃ sub-member in Ordos Basin is rich in pure-shale type shale oil resources, which is expected to actually become a new major strategic replacement area for unconventional oil exploration and development in the basin.