oa The Usefulness of Light Hydrocarbons in Classifying Oman Oils

In order to improve the understanding of the origin of light oils, which have low biomarker<br>concentrations, Petroleum Development Oman (PDO) developed a new classification tool based on the<br>distribution of light hydrocarbons (LHC). This tool proved useful for identifying mixing patterns<br>between light oil/condensate and normal medium and low gravity oils. The database for this study<br>consists of 71 non-biodegraded normal oil/condensate samples from various oil families and sub-oil<br>families of Oman. All oils/condensates were first classified using C15+ compositions. Various plots and<br>parameters based on light hydrocarbons composition (LHC) were collected from literature and used in<br>this study. It is found that the published LHC parameters are very useful tools in classifying Oman oils<br>(e.g. Schaefer parameters, Halpern correlation parameters). In addition to the published parameters,<br>Principal Component Analysis was performed on these samples using the C7 composition (22DMP<br>through to Toluene). Two useful parameters were successfully extracted from the statistical evaluation<br>that can distinguish between various oil families. These are Total DMCPs/n-C7 and (22DMP+24DMP+11DMCP)/ECP.<br>Most of the LHC parameters were able to distinguish between four oil families; Huqf, Athel, Q and<br>Mesozoic (Natih+Tuwaiq) oil families. Each oil family is characterised by a unique LHC distribution.<br>Huqf oils are generally characterised by higher paraffins and lower cycloalkanes than the rest of the oil<br>families. Q oils are characterised by higher branched alkanes than the rest of the oil families. Mesozoic<br>oils (Natih+Tuwaiq) are characterised by higher cycloalkanes than Huqf and Q oils. Apparently, most of<br>the Natih oils have Tuwaiq input and no single oil sample has been found for pure Natih oil. Therefore,<br>most of the plots cluster them together. However, one parameter 22DMP+24DMP+11DMCP/ECP was<br>found to be able to tentatively distinguish between the two oils, Tuwaiq pure oils and Natih/Tuwaiq<br>mixed oils. Both Natih and Tuwaiq oils are characterised by higher cycloalkanes than Huqf and Q oils.<br>Only one sample of apparently pure Silurian ‘Safiq’ oil was available for C7 composition. The<br>composition of this oil was different from the published characteristics of Silurian oils elsewhere in<br>Arabia. We are not able to determine whether our single oil sample is representative for Silurian oils in Oman.