元坝工区须家河组储层测井评价研究

Logging evaluation of the Xujiahe formation in the Yuanba area

元坝工区上三叠统须家河组二段主要发育岩屑砂岩和与推覆事件有关的低角度裂缝,须家河组三段既发育低角度裂缝又发育与隆升事件有关的钙屑砂岩,前者地层含气孔隙度高、测试低产,后者反之,该矛盾难以用传统流体识别方法解释,需开展地质事件的测井研究。为此,分别采用测井曲线地质解析技术中的刻度法和归因法解释上述矛盾的成因。其中,基于岩心、裂缝及溶蚀刻度测井曲线,确定了岩石类型、裂缝及溶蚀的测井识别依据,先后厘清了推覆事件与低角度裂缝的测井识别特征、隆升事件与钙屑溶蚀的测井识别特征;应用低角度裂缝与产能的归因,研制出推覆事件与须二段产能的测井识别图版,应用事件的相互作用归因,发现隆升事件产物钙屑砂岩沿着推覆事件产物低角度裂缝对称溶蚀,这种沿低角度裂缝发育的局部溶蚀高渗带,是须三段低孔却高产的本因,并研制出须三段产能识别图版。新认识合理解释了须家河组两段地层的矛盾,也被新钻井测试所证实。

The second section of the Xujiahe Formation in the Yuanba area mainly contains developed lithic sandstone and low-angle fractures related to nappe events.In the third section,both low-angle fractures and calcareous sandstones related to uplift events are observed.The gas layer in the second section exhibited high porosity and low production during a test,while the opposite trend was shown by the gas layer in the third section.This apparent contradiction is difficult to explain via traditional fluid identification methods.In this regard,an investigation of the logging of geological events can provide clarification to resolve this contradiction.In this study,the calibration and attribution methods were used in the geological analysis of the logging curve to deduce the causes of the contradiction.The cores,fractures,and logging curves of the dissolution etching degree were employed to determine the log identification basis for rock types,fractures,and dissolution.The logging identification features of nappe events and low-angle fractures,as well as those of uplift events and calcium chip dissolution,were clarified.A log identification chart of pushover events and productivity of the second section of the Xujiahe Formation was developed using the attribution of low-angle fractures and productivity.Through attribution of the interaction of the events,it was found that the product of the uplift event(calcareous sandstone)was symmetrically dissolved along the product of the nappe event(low angle fractures).This local dissolution and high permeability zone that developed along low-angle fractures is the root cause of the low porosity but high production of the gas layer in the third section.Additionally,the productivity identification chart was also established.Overall,these new research results can reasonably explain the contradiction between the characteristics of the second and third sections of the Xujiahe Formation,later demonstrated via new drilling tests.