综合运用碳氧同位素和包裹体信息判别古岩溶形成期次

Distinguishing Paleokarst Period by Integrating Carbon-Oxygen Isotopes and Fluid Inclusion Characteristics

岩溶型碳酸盐岩储层是油气勘探开发的重点领域,岩溶发育期次的确定一直是国内外岩溶储层地质建模技术面临的难点。由于现有的岩溶期次判别方法多以暴露特征作为依据,但岩溶作用形式多样,热液等流体活动发生的岩溶作用因缺少暴露标志难以判别。为此,提出一种综合充填物的碳氧同位素判别充填期次和包裹体均一温度判别流体活动期次的岩溶期次判别新方法。以塔里木盆地西北缘奥陶系大量露头资料为基础,进行碳氧同位素测定和包裹体信息分析。利用盐水包裹体测温得到均一温度分布的统计规律,进而得到平均均一温度值,建立按成岩流体活动期次标准划分的平均均一温度直方图。采用碳氧同位素值建立δ13C—δ18 O交会图,根据岩心组合及其切割关系,划分不同充填期次值的分布范围,建立碳氧同位素判别图版。综合碳氧同位素图版和包裹体均一温度图表,进行古岩溶发育期次的判别。将建立的图版应用于哈拉哈塘奥陶系进行岩溶期次的判别,得出哈拉哈塘奥陶系共发育5期岩溶。该结果可与区域地质背景及地震资料解释下的结果较好地吻合。

Paleokarst reservoir is an important target for hydrocarbon exploration and development. Distin guishing of paleokarst development period is always a difficulty facing modeling of paleokarst reservoir The existing methods for ident eokarstification involves various ifying paleokarst period a forms,with some lacking re mostly based on exposure features. But pal- of exposure features,such as hydrothermal flow paleokarstification. Thus, we put forward a comprehensive method involving carbon and oxygen isotopic characteristics of paleokarstic fillings and fluid inclusions characteristics. Based on abundant outcrop data of Tarim Basin,we then analyze the multiple inclusions, and get an average uniform temperature distribution chart based on division of diagenesis sequence. Contrasting discriminant chart of carbon and oxygen iso- topes and inclusions homogenization temperature diagram can be used for judging the paleokarst develop- ment time. The 8la C-3TM O crossplot, according to the combination of core and cutting relation, was divided into different filling period time chart that are included in the distribution range of values. We apply these charts in period distinguishing of Ordovician paleokarst in Halahatang area and get a well matched result with those obtained based on regional geological background and seismic data interpretation.