风化壳地层元素特征与录井识别方法

风化壳作为一种特殊沉积物,对地层划分与对比和沉积相分析具有重要的意义。当前,风化壳之下的碳酸盐岩油气藏、潜山油气藏已成为油气勘探的重要目标区,因此风化壳的识别与卡取往往是该类油气藏钻井施工成败的关键。从风化壳的形成机理入手,结合元素的迁移特性,分析了4个"风化壳剖面"的元素含量和变化趋势,发现以"碳酸盐岩"为母岩的风化壳的元素特征和风化指数特征:①相对于母岩,风化壳具有不迁移和弱迁移元素(Si、Fe、Al、Ti等)相对富集和易迁移元素(Cl、S、Ca、Mg、Na、Mn等)相对流失的特征;②风化壳的风化指标ICW和IPA值要远远高于其母岩的相应指标值。根据这两个主要特征形成了元素录井的风化壳识别和评价方法,通过元素录井的元素含量数据和依据元素含量计算的风化指标,能够较为准确地识别风化壳,并对母岩的风化程度做出定性评价。

Element characteristics and mud logging identification method for weathering crust formation

As a special sediment,weathering crust has an important significance for the stratigraphic division and correlation and sedimentary facies analysis.At present,the carbonate oil and gas reservoirs and buried hill reservoirs under the weathering crust have become an important target area for oil and gas exploration,then the identification and clipping of the weathering crust are often the key to the success of drilling this kind of oil and gas reservoirs.Starting from the forming mechanism of the weathering crust,combined with the migration characteristics of the elements,the authors analyzed 4 elements’ contents of the weathering crust profile and trend,found the elements’ characteristics and weathering characteristics of the index of the weathering crust that takes carbonate as the parent rock:1 related to the parent rock,weathering crust characterized in being rich in the elements of no migration and weak migration(Si,Fe,Al,Ti,etc.) and relative losing the elements of easy migration(Cl,S,Ca,Mg,Na,Mn,etc.),2 the values for weathering index Icw and Ipa of the weathering crust are much higher than its corresponding parent rocks’.According to the two main characteristics,the recognition and evaluation method of the weathering crust for the elements well logging was formed,and it is able to identify the weathering crust accurately by the element content of the element well logging data and the weathering index calculated based on the element contents,and the qualitative evaluation can be made on the weathering degree of the parent rock.