Modified Thermal Maturity Models for Kuwait Basin Through Mud Gas Isotope Logging While Drilling; Benefits of Analyzing δ13C2 and δ13C3 at Wellsite

摘要

Carbon isotopic characterization of mud gas can add great value to the information collected at wellsite and nowadays the interest in this topic is increasing as documented by the study from Poirier et al. (IMOG 2017). The presented study has the objective of illustrating the data logged through a cavity ring-down spectroscopic (CRDS) technique that allowed collection of robust and reliable carbon isotopic data at wellsite. The logged carbon isotopic data were then used for studying the behavior of two formations (Makhul and Najmah) across different fields. Makhul Formation represents the lower most Formation of Cretaceous in Kuwait, representing predominantly as carbonate rock. In lower Makhul, the high gamma radioactivity is due to enrichment of the shales by uranium. While, Najmah formation is an excellent source rock located in upper Jurassic, it consists of black calcareous limestone source rock with high organic content. Both formations are considered as major source rocks for petroleum systems in state of Kuwait. Many standard interpretation models from the literature were screened and adopted in inter-field correlation, resulting in a good matching with the geographical distribution of the fields. The second part of the study will focus on the added value of recording carbon isotopic ratios up to C3. The analysis of δ13C3 is demanding from the instrumental point of view, thus, the benefits in terms of formation evaluation that comes from the logging of isotopes up to C3 will be illustrated in the study. With reference to other literatures, δ13C1 readings might be affected by mixing phenomena with biogenic gases, and thus they are not the best candidates to run maturity assessment through isotopes. Instead, carbon isotopic ratios of ethane and propane are not affected by mixing with biogenic gas, resulting in more robust and accurate interpretations. Few models from literature were applied on collected data, allowing choosing the one that matches best the behavior of the studied basin. Independent measurements on the maturity of the source rock in the area confirmed that the trend highlighted through carbon isotopes logging at wellsite is correct, validating the usefulness of this technique at wellsite.