碳酸盐岩测井层序识别方法研究--以塔中隆起卡1地区奥陶系为例

Study of the method for identification of carbonatite logging sequence stratigraphy——a case study of the Ordovician in the Ka1 area of Tazhong uplift,Tarim basin

进行碳酸盐岩高分辨率的测井层序识别,建立精细等时地层格架,对碳酸盐岩油气勘探开发具有重要的意义。碳酸盐岩颗粒的大小和圆度不能明显地反映水动力作用的过程和能量;成岩作用往往增强储层非均质性,减弱原生沉积旋回性。这些特征使测井曲线对岩性变化与物性好坏的对应关系变差,测井曲线旋回性减弱,测井响应成为多因素作用的综合结果,划分层序所主要依据的沉积旋回特征隐藏在综合响应之中。测井层序识别的关键是多测井参数综合判定泥岩成因,剔除成岩作用后期改造等因素的响应信息,提取对层序划分有用的原生沉积特征信息。通过自然伽马、自然伽马能谱、FMI、地层倾角、双侧向电阻率等测井参数的综合应用,可以较好地识别碳酸盐岩中泥岩成因类型、不整合面,突出原生沉积旋回特征,在塔中隆起卡1地区奥陶系识别出三种泥质成因、两类层序界面。层序分析结果和缝洞统计规律对比表明:较高的泥质含量不利于溶蚀作用的发生;层序对溶孔的纵向分布有着显著的控制作用,而对裂缝的分布影响较弱。

The identification of carbonatite logging sequence stratigraphy and the establishment of high-frequency framework are of great significance for carbonatite oil and gas exploration. The lithologic characteristics of carbonate rocks, such as granulity and circularity could not effectively reflect hydrodynamic process and power; the diagenetic reconstruction often enhances the reservoir＇s heterogeneity and reduces the cyclicity of primary deposits. This would make the relationship of logging responses with lithological changes and physical properties indefinite, and cause the cyclicity of logging curve unnoticeable and the primary sedimentary cyclicity indistinct. The key to the identification of logging sequence stratigraphy is to determine the mud origin, to reject the response from the diagenetic reconstruction, and to extract useful primary depositional information for sequence analysis by using multi-logging parameters. By comprehensively applying GR, SGR, FMI, dip log and DLL we may effectively identify the mud type, the unconformity in the carbonate rock layer, and make the primary deposit cyclicity distinct. We have clearly distinguished three types of mud origin and two kinds of sequence boundary in the Ordovician in the Kal area of Tazhong uplift. The statistical result of the distribution of fractures and vugs indicates that high mud content is unfavorable for karstification, and the sequence boundary has an obvious controlling effect on the vertical distribution of dissolved pores, and a weak affection on the distribution of fractures.