X射线荧光录井岩屑定性判别方法

Qualitative discriminant method for cuttings by X-ray element logging

利用X射线荧光录井技术能够定量检测岩屑中多种元素的含量,获得目标井连续、定量的元素含量数据,为地质录井通过元素含量和变化趋势定性解释岩性提供基本条件。该技术刚刚引进到录井行业,还没有建立根据各类岩石元素组合和含量变化特征及通过多种元素含量数据组合的模型,形成针对砂泥岩、碳酸岩和火成岩的判别指数。通过分析砂泥岩、碳酸岩和火成岩3类岩石的元素特征,依据各种岩性的"主量元素"含量变化,利用岩石学、地球化学的一些方法,参考测井的一些定量解释方法,利用Al、Si、Ca、Mg、Na、K、Fe 7种元素建立了砂岩指数(Isand)、泥岩指数(Ishale)、砂泥比指数(Isand/shale)、碳酸岩指数(Icarb)、灰岩指数(Ilime)、白云岩指数(Idolo)和火成岩指数(Zmag)共7个岩性判别指数。通过多口井实验,利用这7个指数取得了较好的解释效果,岩性解释吻合率达到96.5%以上,能够准确识别火成岩,对砂泥岩剖面中砂质、泥质的解释达到了半定量的程度,对碳酸岩剖面中灰质、白云质可达到定量解释的程度。

Using X-ray element logging technology enables to quantitatively detect the content of a variety of elements in cuttings,obtain continuous,quantitative element content data of the target wells,and provide basic conditions for qualitatively interpreting the lithology through element content and its variation trend.Because the technology has just introduced to mud logging industry,the model has not been set up in accordance with the element combination of various types of rock,the change features of element content and the content combination of varied elements,and there is no form of discriminant index against sand-shale,carbonate and igneous rocks.By analyzing element characteristics of sand-shale,carbonate and igneous rocks,according to the 'major element' content changes of various lithologies,using some methods of petrography and geochemistry,referring some quantitative interpretation methods of well logging,the paper described the establishment of sandstone index(Isand),shale index(Ishale),the index of sand-shale ratio(Isand/shale),carbonate index(Icarb),limestone index(Ilime),dolomite index(Idolo)and igneous index(Zmag),total 7 lithology discriminant indices by using 7 elements of Al,Si,Ca,Mg,Na,K,Fe.Through the experiments in several wells,the use of 7 indices had achieved good interpretation results,lithological interpretation consistent rate was over 96.5%.They can accurately identify igneous rocks.Sabulous and argillaceous interpretation in sand and mudstone profile reached the semiquantitative level,calcareous and dolomitic interpretation in carbonate profiles can achieve the quantitative degree.