深层页岩高分辨率层序地层控制的非均质性特征及其与含气性的关系——以渝西地区Z203井为例

Heterogeneity characteristics of high-resolution sequence stratigraphic control in deep shale and its relationship with gas-bearing:A case study of the well Z203 in western Chongqing Area

非均质性是页岩储层的一项固有性质,是构成页岩储层精细评价、精准预测的重要影响因素。该研究以渝西地区上奥陶—下志留统五峰组—龙一1亚段页岩储层为例,综合测井、钻井岩心编录、薄片观察、有机碳测试及X衍射矿物测试等数据,在建立目标钻孔页岩高分辨率地层层序格架的基础上,表征该套页岩在有机质丰度和矿物组分等方面的非均质性特征,并探讨层序格架控制下的非均质性特征与页岩含气性的关系。研究结果表明:Z203井五峰组—龙一1亚段页岩可以识别出1个长期旋回对应的三级层序(SQ1),3个中期旋回(A-C);Z203井页岩的五峰组—龙一1亚段的矿物组分、TOC及含气性在纵向上表现出较强的非均质性,Z203井页岩中的TOC、石英和白云石含量在垂向上呈现递减的趋势,黏土矿物和长石向上呈逐渐增加的趋势。含气量整体呈现向上递减趋势。A旋回时期的石英、TOC及含气量明显高于B-C旋回时期,C旋回时期黏土矿物含量最高;在沉积演化过程中非均质性通过控制页岩储层的原始物质(物质成分)进而控制页岩储层特征最后影响储层的含气性。剖析非均质性对含气性的控制机理,可以为页岩气资源评价及预测提供科学依据。

Heterogeneity is an inherent property of shale reservoirs,which constitutes an important influencing factor for fine evaluation and accurate prediction of shale reservoirs.Taking the Upper Ordovician-Lower Silorian Wufeng Formation-Longyi1 subsection shale reservoir in the western Chongqing region as an example,the data of logging,drilling core cataloging,flake observation,organic carbon testing,and X diffraction mineral testing were used to characterize the heterogeneity characteristics of the shale in terms of organic matter abundance and mineral composition on the basis of establishing a high-resolution stratigraphic lattice frame for target drilling shale,and to explore the relationship between the heterogeneity characteristics of the shale under the control of the sequence lattice and the gas content of the shale.The results show that the shale of the Wufeng Formation-Longyi1 subsection of well Z203 can identify a three-stage sequence(SQ1)corresponding to a long-term cycle and three medium-term cycles(A-C);The mineral composition,TOC and gas-bearing of the Wufeng Formation-Longyi1 subsection of the well Z203 shale show a strong heterogeneity in the vertical direction,and the TOC,quartz and dolomite content in the well Z203 shale show a decreasing trend in the vertical direction,and the clay minerals and feldspar show a gradual upward trend.The gas content as a whole showed an downward trend.The content of quartz,TOC and gas content in the A cycle period was significantly higher than that in the B-C cycle period,and the mineral content of clay in the C cycle period was the highest;heterogeneity in the sedimentary evolution process finally affected the gas-bearing of the shale reservoir by controlling the original material(material composition)of the shale reservoir.Analyzing the control mechanism of heterogeneity over gas content can provide a scientific basis for the evaluation and prediction of shale gas resources.