已开发出两种星状图(极坐标多变量标绘图)用于估价石油之间的微小化学差别。这种星状图以分析由气相色谱法分离的原油的C_7烃为基础。首先,用这种C_7图鉴别由水洗、生物降解作用、脱水等因素转化而引起的油的变化。在该图上标绘了根据降低生物降解灵敏度的顺序排列的8个比值,这些比值标为Tr1—Tr8,这种图被称为C_7油转化星状图(C_7OTSD)。其次,C_7基础图包括由具有很强抗转化影响能力的化合物组成的5个比值,因而对对比很有用。这些比值标为C1—C5,标绘在C_7油相关星状图(C_7OCSD)上。这种图可以根据与油源有关的化学差异来对比转化油和原始油,而用最常规的地球化学方法却不易完成这个任务。例如,凝析油由于其高成熟度常不包含生物标志,因此不能与低成熟度油对比。不过,凝析油和油通常都含有可以通过C_7基础星状图进行对比的轻烃。星状图分成两种类型,允许在一组油中根据C_7OCSD来估价转化的相对程度。这些微相关可以检测油与油之间很小的化学差别,因此,可以得知,相同储层中油与油之间甚至更轻微的变化也是准许的。这项技术在勘探与生产中都有广泛的应用。与生产有关的用途包括:储层划分研究、调查储层范围和连通性、测定套管泄漏源以及测定多层完成井(或漏隙单层完成井)中来自不同储层的油混合的范围。可列举的勘探问题有:油田充满过程的机理和模式以及对未做试验补偿带的油质的评价。大多数这些问题可以通过简单而有效地分析生产或试验原油予以解决,比如,在生产应用中的一大优点,就是在任意井中不停产的情况下直接估价储层连通性的能力。这项技术的另一用途是研究污染物质或者在炼油厂作业线中初步提炼油。在沙特阿拉姆科(Saudi Aramco)已经做过几种研究。这些研究包括:套管后期泄漏的3个实例、油鉴别的两个实例、凝析油对比和炼油厂污染物质追踪的实例各一个。 Two star charts (polar coordinate multivariate plots) have been developed to assess the small chemical differences between petroleum. This star chart is based on the analysis of C7 hydrocarbons of crude oils separated by gas chromatography. First of all, use this C_7 chart to identify the changes in oil caused by the conversion of factors such as water washing, biodegradation, and dehydration. The graph plots eight ratios according to the order of decreasing biodegradability, these ratios being labeled Tr1-Tr8 and this plot is referred to as C_7 oil-transformed star chart (C_7OTSD). Second, the C7 basal map includes five ratios made up of compounds that have strong resistance to transformation and are therefore useful for comparison. These ratios, labeled C1-C5, are plotted on the C_7 oil-related star chart (C_7OCSD). This plot compares the conversion oil to the crude oil based on chemical differences associated with the oil source, which is not easily accomplished by the most common geochemical methods. For example, condensate can not be compared with low-maturity oils due to its high maturity, which often does not contain biomarkers. However, condensates and oils often contain light hydrocarbons that can be compared on a C_7 base chart. Star charts are divided into two types, which allow the relative degree of conversion to be estimated from a set of oils based on C_7OCSD. These micro correlations can detect very small chemical differences between oil and oil, so that even less minor changes between oil and oil in the same reservoir are permitted. This technology has a wide range of applications in exploration and production. Production-related uses include study of reservoir division, investigation of reservoir range and connectivity, determination of casing leak sources, and determination of the extent of oil mixing from different reservoirs in multi-well completion (or single-well completion) . Examples of exploration issues that can be enumerated are: Mechanisms and patterns of oilfield fill-up and evaluation of the oiliness of non-tested compensation zones. Most of these problems can be solved by simply and effectively analyzing the production or testing of crude oil. For example, one of the major advantages in manufacturing applications is the ability to directly evaluate reservoir connectivity without shutting down production in any well. Another use of this technology is to study contaminants or to refine the oil initially in refinery operations. Several studies have been done at Saudi Aramco. These included three examples of post-casing leaks, two examples of oil identification, one for condensate comparison, and one for refinery contaminant tracking.