陆相富有机质页岩脆性评价方法优选与应用——以渤海湾盆地沧东凹陷孔二段为例

Optimization and application of brittleness evaluation methods for continental organic-rich shale:A case study of the 2nd Member of Kongjiadian Formation,Cangdong Sag,Bohai Bay Basin

页岩脆性是影响压裂裂缝规模、决定页岩滞留烃能否可动的关键指标之一,是页岩油平面甜点区、水平井钻探甜点靶层、压裂甜点段评价的主要参数之一。通过沧东凹陷孔二段17块页岩样品的X衍射矿物分析、有机碳分析以及岩石三轴力学实验,建立了以长英质矿物、碳酸盐、黏土、有机质为骨架的页岩脆性地质模型和5个基于矿物成分的页岩脆性评价公式。通过与力学参数脆性公式对比分析,优选出综合考虑页岩总有机碳含量、不同矿物脆度的脆性评价新方法以及简化的TOC、黏土两项关键参数的脆性评价方法,前者适用于XRD分析矿物成分资料丰富的层段,后者适用于测井评价。应用矿物含量法评价G108-8井孔二段C6层脆性,并结合含油性优选出高脆、高含油或中等含油的页岩作为工程-含油双甜点,Z1608和GX5井的试油结果验证了上述脆性评价方法在页岩油勘探中的有效性,为页岩油甜点段和压裂方案的设计提供了重要参考。

Shale brittleness is one of the key indexes affecting dimensions of hydraulic fractures and determining the producibility of trapped hydrocarbons in shale.Therefore,it is one of the major parameters for evaluation of the planar sweet-spot zone,horizontal drilling sweet-spot target,and sweet-spot hydraulic fracturing stage.The shale brittleness geological model was built on the framework of the felsic mineral,carbonate,clay,and organic matter,and five shale brittleness evaluation formulas based on mineral composition were developed,via the X-ray diffraction(XRD) mineral analysis,TOC measurement,and tri-axial rock mechanic tests of 17 shale samples collected from the 2 nd Member of the Kongjiadian Formation in the Cangdong sag.The novel brittleness evaluation method that comprehensively incorporates TOC and brittleness of various minerals,and the simplified brittleness evaluation considering two key parameters(namely TOC and clays) were selected via the comparison with the brittleness formula based on rock mechanic parameters.The former applies to intervals with sufficient XRD mineral analysis data,while the latter applies to well logging evaluation.The mineral composition-based method was applied to the C6 interval of the 2 nd Member of the Kongjiadian Formation in Well G108-8,which also considered the oil content,and the shale interval with high brittleness,and high or medium oil content was identified as the engineering-oil content dual sweet-spot.The formation testing results of Wells Z1608 and GX5 validated the effectiveness of the developed brittleness evaluation method for shale oil exploration and the vital guidance on sweet-spot stage identification and hydraulic fracturing design.