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    宁夏六盘山盆地白垩系马东山组页岩气地质特征与勘探潜力分析

    Geological characteristics and shale gas exploration prospect analysis of Cretaceous Madongshan Formation in Liupanshan Basin, Ningxia

    • 摘要: 以六盘山盆地固页1井白垩系马东山组泥页岩为研究对象,通过野外观察、岩心编录、岩石热解、X衍射、干酪根元素分析、等温吸附等手段,对六盘山盆地固页1井白垩系马东山组页岩气勘探潜力进行评价。结果表明:(1)六盘山盆地白垩系马东山组具有丰富的荧光、油迹、沥青等油气显示,并见200余米的暗色泥页岩、油页岩层位。(2)马东山组泥页岩有机质类型为Ⅱ~Ⅲ型;65%样品TOC大于1.0%,37.2%的样品TOC大于2.0%;50%样品Ro大于0.8%,Tmax处于435~445℃,处于低成熟—成熟阶段,属生物成因气与热成因气混合气。(3)马东山组泥页岩具黏土矿物低,长石类和碳酸盐类矿物含量高的特征,碳酸盐类矿物均值达38.2%,长石类含量均值24.4%,石英含量均值17.2%,黏土含量均值仅为13.2%;符合页岩气压裂施工的黏土含量小于30%,脆性矿物含量大于40%标准。其黏土组成以伊利石和伊/蒙间层为主,均值含量分别达69%、26.1%。(4)马东山组泥页岩有效孔隙度介于0.117%~1.268%;渗透率0.0009~0.0042 mD,属低孔低渗储层。马东山组泥页岩具有较强的储气能力,其最大甲烷吸附能力介于0.96~4.6 m3/t,均值2.29 m3/t。(5)对比延安组页岩地质、地化参数,认为六盘山盆地白垩系马东山组泥页岩层位具备较好的页岩气勘探潜力,可以作为良好的页岩气层位进行进一步工作,其成果将对河西走廊白垩系非常规油气层位勘探具有借鉴意义。

       

      Abstract: Clay shale samples from Cretaceous Madongshan Formation in Well Guye 1 in Liupanshan Basin were collected for determining shale gas exploration prospect through outcrops and core description, rock pyrolysis, X-ray diffraction, and element analysis of kerogen and isothermal adsorption. The following conclusions have been reached:(1) Cretaceous Madongshan Formation of Liupanshan Basin has abundant oil gas shows consisting of fluorescence, oil stains, bitumen and dark shale or oil shale, with a thickness nearly 200 meters in core Guye1. (2) The organic matter type of Madongshan Formation is Ⅱand Ⅲ, the 65% shale samples of Madongshan Formation in core Guye1 have a TOC content higher than 1.0%, with 37.2% shale samples having TOC content higher than 2.0%. The vitrinite reflectance of nearly half samples is higher than 0.8%, and the Tmax is 435~445℃, suggesting that Madongshan Formation is at the low mature to mature stage, and gas reservoir is mixture of biogenic gas and thermal genetic gase. (3) The shale of Madongshan Formation has characteristics of low clay content and higher feldspar and carbonates. The average content of carbonate, feldspar, quartz and clay is 38.2%, 24.4%, 17.2% and 13.2%, respectively, which can meet the demand of shale gas exploration standard of clay content less than 30% and brittle mineral content higher than 40%. The components of clay are mainly illite and illite-montmorillonite, with the average content being 69% and 26.1%. The porosity is between 0.117% and 1.268%, the permeability is between 0.0009 mD and 0.0042 mD, suggesting a low porosity and low permeability reservoir. The isothermal adsorption test shows that Madongshan shale has a strong gas storage capacity, with the methane content being 0.96-4.6 m3/t and the average content being 2.26 m3/t. (4) According to a comparison of geological and geochemical characteristics with shale of Yanan Formation, the authors hold that Madongshan Formation of Liupanshan Basin has a huge shale gas exploration potential and could be regarded as a high quality shale gas reservoir for exploration and development, and the achievements obtained by the authors provide experience for exploration of the unconventional oil and gas reservoirs in the Cretaceous strata of the Hexi Corridor.

       

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