致密砂岩裂缝测井识别特色技术及其应用效果——以四川盆地川西坳陷新场气田上三叠统须家河组二段为例

Characteristics and application effect of logging-based fracture identification in tight sandstones:A case study of the Upper Triassic Xu 2 Member in Western Sichuan Depression,Sichuan Basin

裂缝是致密砂岩储层高产、稳产的一个关键因素,由于受常规测井分辨率低、致密砂岩岩性和物性变化快以及裂缝发育规模小且产状多变等因素影响,常规测井裂缝识别符合率偏低。以川西坳陷新场气田须家河组二段致密砂岩为例,在总结区域裂缝类型和裂缝测井响应特征的基础上,创新性地提取电阻率降低因子和时差增大因子等多种裂缝敏感因子,以及电阻率维度与声波维度约束指标,在放大裂缝信号的同时压制干扰影响,并首次采用灰色关联确定敏感因子权重系数,加权计算裂缝指示曲线,利用阈值约束实现裂缝识别,进一步通过与裂缝响应模式库对比,聚类识别裂缝类型。与X5和X101等5口井电成像对比,裂缝识别符合率达到90%以上,为研究致密砂岩裂缝展布规律、储层类型评价以及产能预测等提供了可靠依据。

Fractures are a key factor for high and stable production of tight sandstone reservoirs.The coincidence rate of fracture identification based on conventional logging is,however,low,due to the low resolution of conventional logging,rapid change of lithology and physical properties of tight sandstone,small-scale fractures with variable occurrences.Based on the concluded regional fracture types and fracture logging response characteristics,we innovatively extract multiple factors sensitive to fracture such as resistivity reduction and moveout augmentation in the tight sandstone of the second member of Xujiahe Formation(hereinafter referred to as Xu 2 Member)in Xinchang gas field,Western Sichuan Depression.Furthermore,resistivity dimension and acoustic dimension constraint index are selected to suppress the interference effect with the amplification of fracture signals;and the gray correlation is applied for the first time to determine the weight coefficient of sensitive factors,the fracture indication curve is calculated by weighting,and the threshold constraint is used to identify fractures.In comparison with the fracture response pattern library,the fracture type is identified by clustering.In comparing with electric imaging data of the 5 wells including Wells X5 and X101,the coincidence rate of fracture identification reaches up to more than 90%,providing a favorable basis for the study of fracture distribution pattern,reservoir type evaluation and productivity prediction of tight sandstones.